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Archive for January, 2011

New research from last week 4/2011

Posted by Ari Jokimäki on January 31, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Human fingerprint in extremely warm days

The role of human activity in the recent warming of extremely warm daytime temperatures – Christidis et al. (2011) “Formal detection and attribution analyses of changes in daily extremes give evidence of a significant human influence on the increasing severity of extremely warm nights and decreasing severity of extremely cold days and nights. We present an optimal fingerprinting analysis, which also detects the contributions of external forcings to recent changes in extremely warm days using non-stationary extreme value theory. Our analysis is the first that attempts to partition the observed change in warm daytime extremes between its anthropogenic and natural components and hence attribute part of the change to possible causes. Changes in the extreme temperatures are represented by the temporal changes in a parameter of an extreme value distribution. Regional distributions of the trend in the parameter are computed with and without human influence using constraints from the global optimal fingerprinting analysis. Anthropogenic forcings alter the regional distributions, indicating that extremely warm days have become hotter.” Nikolaos Christidis, Peter A. Stott, Simon J. Brown, Journal of Climate 2011.

Extreme 2009/2010 arctic oscillation behaved abnormally

Sea ice response to an extreme negative phase of the Arctic Oscillation during winter 2009/2010 – Stroeve et al. (2011) “Based on relationships established in previous studies, the extreme negative phase of the Arctic Oscillation (AO) that characterized winter of 2009/2010 should have favored retention of Arctic sea ice through the 2010 summer melt season. The September 2010 sea ice extent nevertheless ended up as third lowest in the satellite record, behind 2007 and barely above 2008, reinforcing the long-term downward trend. This reflects pronounced differences in atmospheric circulation during winter of 2009/2010 compared to the mean anomaly pattern based on past negative AO winters, low ice volume at the start of the melt season, and summer melt of much of the multiyear ice that had been transported into the warm southerly reaches of the Beaufort and Chukchi seas.” Stroeve, J. C., J. Maslanik, M. C. Serreze, I. Rigor, W. Meier, and C. Fowler (2011), Geophys. Res. Lett., 38, L02502, doi:10.1029/2010GL045662.

Ocean acidification has negative impact to Caribbean corals

Ocean acidification impacts multiple early life history processes of the Caribbean coral Porites astreoides – Albright & Langdon (2011) “Ocean acidification (OA) refers to the increase in acidity (decrease in pH) of the ocean’s surface waters resulting from oceanic uptake of atmospheric CO2. Mounting experimental evidence suggests that OA threatens numerous marine organisms, including reef-building corals. Coral recruitment is critical to the persistence and resilience of coral reefs and is regulated by several early life processes, including: larval availability (gamete production, fertilization, etc.), larval settlement, post-settlement growth and survival. Environmental factors that disrupt these early life processes can result in compromised or failed recruitment and profoundly affect future population dynamics. To evaluate the effects of OA on the sexual recruitment of corals, we tested larval metabolism, larval settlement, and post-settlement growth of the common Caribbean coral Porites astreoides at three pCO2 levels: ambient seawater (380 μatm) and two pCO2 scenarios that are projected to occur by the middle (560 μatm) and end (800 μatm) of the century. Our results show that larval metabolism is depressed by 27% and 63% at 560 and 800 μatm respectively compared to controls. Settlement was reduced by 42–45% at 560 μatm and 55–60% at 800 μatm, relative to controls. Results indicate that OA primarily affects settlement via indirect pathways, whereby acidified seawater alters the substrate community composition, limiting the availability of settlement cues. Post-settlement growth decreased by 16% and 35% at 560 and 800 μatm respectively, relative to controls. This study demonstrates that OA has the potential to negatively impact multiple early life history processes of P. astreoides and may contribute to substantial declines in sexual recruitment that are felt at the community and/or ecosystem scale.” Rebecca Albright, Chris Langdon, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02404.x.

Early Toarcian mass extinction possibly due to rapid warming

Mass extinction and recovery of the early toarcian (early Jurassic) brachiopods linked to climate change in Northern and Central Spain – Joral et al. (2011) “The Early Toarcian mass extinction event represented the most important Mesozoic and Cenozoic turnover of the population of brachiopods and severely affected other benthic fauna. Two main hypotheses have been proposed to explain the synchronous and global mass extinction: an oceanic anoxic event or a warming episode. To test both hypotheses, the dynamics of the brachiopod assemblages below and above the extinction boundary are analyzed and compared with the seawater palaeotemperature variations, calculated from the δ18O data recorded in belemnite rostra. Five sections from Northern and Central Spain, well dated with ammonites, have been selected for this study. The sections show no indication of sedimentary breaks and contain abundant brachiopods, which have been grouped into four assemblages. The changes observed in the brachiopod assemblages show a close correlation with the changes in the seawater palaeotemperatures. The oldest assemblage (assemblage 1) coincides with a cooling interval recorded to have taken place in the latest Pliensbachian. Palaeobiogeographical reconstruction shows that this assemblage was distributed at palaeolatitudes between 30 and 45ºN, with a preference for relatively cool waters. With the rise of temperatures that took place during the earliest Toarcian Tenuicostatum Zone, assemblage 1 was substituted by assemblage 2, composed of different species of the same genera but considerably restricted to the warmer waters of lower palaeolatitudes, between 28 and 35ºN. Coinciding with the rapid and pronounced increase in sea water temperature, recorded at the Tenuicostatum − Serpentinum zonal boundary, all of these brachiopod species disappeared in the studied localities, marking clearly the extinction boundary. Predominant southward currents through the Laurasian Seaway precluded the possible migration of the brachiopods to cooler northern waters. The brachiopods disappearance is independent from the oxygenation degree of the sea bottom, and therefore the rapid warming seems to be the most plausible cause of the mass extinction. After the extinction event, the recovery of the brachiopods was uneven. Subsequent to a brief pause, recovery was rapid in Central Spain and in other southern areas of Western Tethys, whereas in northern Spain and in the whole of Europe north of the French Central Massif, brachiopods did not recover until the Mid to Late Toarcian times” Fernando García Joral, Juan J. Gómez, and Antonio Goy, Palaeogeography, Palaeoclimatology, Palaeoecology, doi:10.1016/j.palaeo.2011.01.023.

Extreme rainfall frequency in Brazil has increased

Trends in the Frequency of Intense Precipitation Events in Southern and Southeastern Brazil during 1960–2004 – da Silva Teixeira (2011) “A new approach to define heavy and extreme rainfall events based on cluster analysis and area-average rainfall series is presented. The annual frequency of the heavy and extreme rainfall events are obtained for Southeastern and Southern Brazil regions. In the 1960–2004 period, 510 (98) and 466 (77) heavy (extreme) rainfall events are identified in the two regions. Monthly distributions of the events closely follow the monthly climatological rainfall in the two regions. In both regions, annual heavy and extreme rainfall event frequencies present increasing trends in the 45-year period. However, only in Southern Brazil is the trend statistically significant. Although longer time series are necessary to ensure the existence of long term trends, the positive trends are somewhat alarming since they indicate that climate changes, in terms of rainfall regimes, are possibly under way in Brazil.” Mateus da Silva Teixeira, Journal of Climate, 2011.

Forests change to lighter color -> negative feedback

Boreal lichen woodlands: A possible negative feedback to climate change in eastern North America – Bernier et al. (2011) “Because of successive forest fires, closed-canopy black spruce forests are susceptible to a shift towards open lichen–spruce woodlands in parts of the boreal forest of eastern North America. The shift from dark black spruce canopies to pale lichen ground cover offers a dramatic contrast in reflectance that may compensate for the CO2 emissions from forest fires in terms of radiative forcing. We have therefore looked at the climate change feedback that would result from the generation of lichen woodlands through changes in albedo and in stored carbon. Using albedo estimates based on MODIS imagery and incoming solar radiation for the period between 2000 and 2008 along with forest biomass estimates for eastern Canada, we have estimated that net radiative forcing for the conversion from closed-canopy coniferous forests to open lichen woodlands would be about −0.12 nW m−2 ha−1, and would therefore generate a cooling effect in the atmosphere. Based on current estimates of area in open lichen woodlands within the closed-canopy black spruce–moss forests of eastern Canada, we estimate that a current net forcing of −0.094 mW m−2 has already arisen from such conversions. As projections of future climate have been linked to increased probability of forest fires, the generation of open lichen woodlands provides a possible negative feedback to climate change. Results also suggest that carbon sequestration through the afforestation of boreal lichen woodlands may not provide a climate change mitigation benefit.” P.Y. Bernier, R.L. Desjardins, Y. Karimi-Zindashty, D. Worth, A. Beaudoin, Y. Luo and S. Wang, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2010.12.013.

West Antarctica warming trends and causes

An assessment and interpretation of the observed warming of West Antarctica in the austral spring – Schneider et al. (2011) “We synthesize variability and trends in multiple analyses of Antarctic near-surface temperature representing several independent source datasets and spatially complete reconstructions, and place these into the broader context of the behavior of other components of the climate system during the past 30–50 years. Along with an annual-mean trend during the past 50 years of about 0.1°C/decade averaged over Antarctica, there is a distinct seasonality to the trends, with insignificant change (and even some cooling) in austral summer and autumn in East Antarctica, contrasting with warming in austral winter and spring. Apart from the Peninsula, the seasonal warming is largest and most significant in West Antarctica in the austral spring since the late 1970s. Concurrent trends in sea ice are independent evidence of the observed warming over West Antarctic, with the decrease in sea ice area in the Amundsen and Bellingshausen Seas congruent with at least 50% of the inland warming of West Antarctica. Trends in near surface winds and geopotential heights over the high-latitude South Pacific are consistent with a role for atmospheric forcing of the sea ice and air temperature anomalies. Most of the circulation trend projects onto the two Pacific South American (PSA) modes of atmospheric circulation variability, while the Southern Annular Mode lacks a positive trend in spring that would otherwise cause a cooling tendency. The largest circulation trend is associated with the PSA-1 mode, a wave-train extending from the tropics to the high Southern latitudes. The PSA-1 mode is significantly correlated with SSTs in the southwestern tropical and subtropical Pacific. The increased SSTs in this region, together with the observed increase in rainfall, suggest that anomalous deep convection has strengthened or increased the occurrence of the Rossby wave-train associated with PSA-1. This hypothesis is supported by results from two ensembles of SST-forced atmospheric general circulation model simulations. Finally, the implications of the seasonality, timing, and spatial patterns of Antarctic temperature trends with respect to interpreting the relative roles of stratospheric ozone depletion, SSTs and increased atmospheric concentrations of greenhouse gasses are discussed.” David P. Schneider, Clara Deser and Yuko Okumura, Climate Dynamics, DOI: 10.1007/s00382-010-0985-x. [full text]

Tropical cyclones last longer since 1975

Increasing duration of tropical cyclones over China – Chen et al. (2011) “Tropical cyclone (TC) damage is closely associated with the time TCs spend over land. After examining 233 TCs that formed over the western North Pacific and then made landfall over China mainland during 1951–2009, this study shows a significant increase in the annual average overland duration of a TC over the past 35 years from 1975 to 2009, while no significant trend can be detected in the annual frequency. The increasing duration over land is consistent with the increasing rainfall associated with the landfall TCs and changes in the large-scale steering flow. It seems that the decreasing vertical wind shear allows the landfall TCs to increase survival time over land during the past 35 years.” Chen, X., L. Wu, and J. Zhang (2011), Geophys. Res. Lett., 38, L02708, doi:10.1029/2010GL046137.

Tipping point not likely to occur for arctic sea ice

Recovery mechanisms of Arctic summer sea ice – Tietsche et al. (2011) “We examine the recovery of Arctic sea ice from prescribed ice-free summer conditions in simulations of 21st century climate in an atmosphere–ocean general circulation model. We find that ice extent recovers typically within two years. The excess oceanic heat that had built up during the ice-free summer is rapidly returned to the atmosphere during the following autumn and winter, and then leaves the Arctic partly through increased longwave emission at the top of the atmosphere and partly through reduced atmospheric heat advection from lower latitudes. Oceanic heat transport does not contribute significantly to the loss of the excess heat. Our results suggest that anomalous loss of Arctic sea ice during a single summer is reversible, as the ice–albedo feedback is alleviated by large-scale recovery mechanisms. Hence, hysteretic threshold behavior (or a “tipping point”) is unlikely to occur during the decline of Arctic summer sea-ice cover in the 21st century.” Tietsche, S., D. Notz, J. H. Jungclaus, and J. Marotzke (2011), Geophys. Res. Lett., 38, L02707, doi:10.1029/2010GL045698.

Stratospheric water vapor has increased in Colorado

Stratospheric water vapor trends over Boulder, Colorado: Analysis of the 30 year Boulder record – Hurst et al. (2011) “Trend analyses are presented for 30 years (1980–2010) of balloon-borne stratospheric water vapor measurements over Boulder, Colorado. The data record is broken into four multiple-year periods of water vapor trends, including two that span the well-examined but unattributed 1980–2000 period of stratospheric water vapor growth. Trends are determined for five 2 km stratospheric layers (16–26 km) utilizing weighted, piecewise regression analyses. Stratospheric water vapor abundance increased by an average of 1.0 ± 0.2 ppmv (27 ± 6%) during 1980–2010 with significant shorter-term variations along the way. Growth during period 1 (1980–1989) was positive and weakened with altitude from 0.44 ± 0.13 ppmv at 16–18 km to 0.07 ± 0.07 ppmv at 24–26 km. Water vapor increased during period 2 (1990–2000) by an average 0.57 ± 0.25 ppmv, decreased during period 3 (2001–2005) by an average 0.35 ± 0.04 ppmv, then increased again during period 4 (2006–2010) by an average 0.49 ± 0.17 ppmv. The diminishing growth with altitude observed during period 1 is consistent with a water vapor increase in the tropical lower stratosphere that propagated to the midlatitudes. In contrast, growth during periods 2 and 4 is stronger at higher altitudes, revealing contributions from at least one mechanism that strengthens with altitude, such as methane oxidation. The amount of methane oxidized in the stratosphere increased considerably during 1980–2010, but this source can account for at most 28 ± 4%, 14 ± 4%, and 25 ± 5% of the net stratospheric water vapor increases during 1980–2000, 1990–2000, and 1980–2010, respectively.” Hurst, D. F., S. J. Oltmans, H. Vömel, K. H. Rosenlof, S. M. Davis, E. A. Ray, E. G. Hall, and A. F. Jordan (2011), J. Geophys. Res., 116, D02306, doi:10.1029/2010JD015065.

The Twentieth Century Reanalysis Project

The Twentieth Century Reanalysis Project – Compo et al. (2011) “The Twentieth Century Reanalysis (20CR) project is an international effort to produce a comprehensive global atmospheric circulation dataset spanning the twentieth century, assimilating only surface pressure reports and using observed monthly sea-surface temperature and sea-ice distributions as boundary conditions. It is chiefly motivated by a need to provide an observational dataset with quantified uncertainties for validations of climate model simulations of the twentieth century on all time-scales, with emphasis on the statistics of daily weather. It uses an Ensemble Kalman Filter data assimilation method with background ‘first guess’ fields supplied by an ensemble of forecasts from a global numerical weather prediction model. This directly yields a global analysis every 6 hours as the most likely state of the atmosphere, and also an uncertainty estimate of that analysis. The 20CR dataset provides the first estimates of global tropospheric variability, and of the dataset’s time-varying quality, from 1871 to the present at 6-hourly temporal and 2° spatial resolutions. Intercomparisons with independent radiosonde data indicate that the reanalyses are generally of high quality. The quality in the extratropical Northern Hemisphere throughout the century is similar to that of current three-day operational NWP forecasts. Intercomparisons over the second half-century of these surface-based reanalyses with other reanalyses that also make use of upper-air and satellite data are equally encouraging. It is anticipated that the 20CR dataset will be a valuable resource to the climate research community for both model validations and diagnostic studies. Some surprising results are already evident. For instance, the long-term trends of indices representing the North Atlantic Oscillation, the tropical Pacific Walker Circulation, and the Pacific–North American pattern are weak or non-existent over the full period of record. The long-term trends of zonally averaged precipitation minus evaporation also differ in character from those in climate model simulations of the twentieth century.” G. P. Compo et al., Quarterly Journal of the Royal Meteorological Society, Volume 137, Issue 654, pages 1–28, January 2011 Part A, DOI: 10.1002/qj.776.

See also the website of 20th century reanalysis.

Last glacial maximum CO2 and carbon-13 finally explained

Last Glacial Maximum CO2 and δ13C successfully reconciled – Bouttes et al. (2011) “During the Last Glacial Maximum (LGM, ∼21,000 years ago) the cold climate was strongly tied to low atmospheric CO2 concentration (∼190 ppm). Although it is generally assumed that this low CO2 was due to an expansion of the oceanic carbon reservoir, simulating the glacial level has remained a challenge especially with the additional δ13C constraint. Indeed the LGM carbon cycle was also characterized by a modern-like δ13C in the atmosphere and a higher surface to deep Atlantic δ13C gradient indicating probable changes in the thermohaline circulation. Here we show with a model of intermediate complexity, that adding three oceanic mechanisms: brine induced stratification, stratification-dependant diffusion and iron fertilization to the standard glacial simulation (which includes sea level drop, temperature change, carbonate compensation and terrestrial carbon release) decreases CO2 down to the glacial value of ∼190 ppm and simultaneously matches glacial atmospheric and oceanic δ13C inferred from proxy data. LGM CO2 and δ13C can at last be successfully reconciled.” Bouttes, N., D. Paillard, D. M. Roche, V. Brovkin, and L. Bopp (2011), Geophys. Res. Lett., 38, L02705, doi:10.1029/2010GL044499.

Arctic permafrost might change to carbon source in 2020’s

Amount and timing of permafrost carbon release in response to climate warming – Schaefer et al. (2011) “The thaw and release of carbon currently frozen in permafrost will increase atmospheric CO2 concentrations and amplify surface warming to initiate a positive Permafrost Carbon Feedback (PCF) on climate. We use surface weather from three Global Climate Models based on the moderate warming, A1B Intergovernmental Panel on Climate Change emissions scenario and the SiBCASA land surface model to estimate the strength and timing of the PCF and associated uncertainty. By 2200, we predict a 29–59% decrease in permafrost area and a 53–97 cm increase in active layer thickness. By 2200, the PCF strength in terms of cumulative permafrost carbon flux to the atmosphere is 190 ± 64 Gt C. This estimate may be low because it does not account for amplified surface warming due to the PCF itself and excludes some discontinuous permafrost regions where SiBCASA did not simulate permafrost. We predict that the PCF will change the Arctic from a carbon sink to a source after the mid 2020s and is strong enough to cancel 40–88% of the total global land sink. The thaw and decay of permafrost carbon is irreversible and accounting for the PCF will require larger reductions in fossil fuel emissions to reach a target atmospheric CO2 concentration.” Kevin Schaefer, Tingjun Zhang, Lori Bruhwiler, Andrew P. Barrett, 2011, Tellus B, DOI: 10.1111/j.1600-0889.2011.00527.x.


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Papers on Younger Dryas cold event

Posted by Ari Jokimäki on January 27, 2011

This is a list of papers on Younger Dryas cold event. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

North Atlantic Deep Water and climate variability during the Younger Dryas cold period – Elmore & Wright (2011) “The Younger Dryas, the last large millennial-scale climate oscillation (12.9–11.6 ka), has been widely attributed to a massive meltwater discharge event that disrupted ocean circulation and plunged the circum–North Atlantic back into a near-glacial state. Low-resolution deep-water reconstructions indicate lower North Atlantic Deep Water (NADW) production during the Younger Dryas, though the Δ14C record requires some deep-water production. Herein, we reconstruct deep-water mass variations using a southern Gardar Drift sediment core with an expanded Younger Dryas section. We show that southern-sourced water invaded the deep North Atlantic to start the Younger Dryas, but was replaced by NADW within 500 yr. Southern-sourced waters briefly reappeared at the end of the Younger Dryas. These deep-water reorganizations to start and end the Younger Dryas suggest that increased meltwater fluxes were limited temporally and focused on regions where deep-water convection occurred during the deglaciation.” Aurora C. Elmore and James D. Wright, Geology, v. 39 no. 2 p. 107-110, doi: 10.1130/G31376.1.

Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean – Murton et al. (2010) “The melting Laurentide Ice Sheet discharged thousands of cubic kilometres of fresh water each year into surrounding oceans, at times suppressing the Atlantic meridional overturning circulation and triggering abrupt climate change. Understanding the physical mechanisms leading to events such as the Younger Dryas cold interval requires identification of the paths and timing of the freshwater discharges. Although Broecker et al. hypothesized in 1989 that an outburst from glacial Lake Agassiz triggered the Younger Dryas, specific evidence has so far proved elusive, leading Broecker to conclude in 2006 that “our inability to identify the path taken by the flood is disconcerting”. Here we identify the missing flood path—evident from gravels and a regional erosion surface—running through the Mackenzie River system in the Canadian Arctic Coastal Plain. Our modelling of the isostatically adjusted surface in the upstream Fort McMurray region, and a slight revision of the ice margin at this time, allows Lake Agassiz to spill into the Mackenzie drainage basin. From optically stimulated luminescence dating we have determined the approximate age of this Mackenzie River flood into the Arctic Ocean to be shortly after 13,000 years ago, near the start of the Younger Dryas. We attribute to this flood a boulder terrace near Fort McMurray with calibrated radiocarbon dates of over 11,500 years ago. A large flood into the Arctic Ocean at the start of the Younger Dryas leads us to reject the widespread view that Agassiz overflow at this time was solely eastward into the North Atlantic Ocean.” Julian B. Murton, Mark D. Bateman, Scott R. Dallimore, James T. Teller & Zhirong Yang, Nature 464, 740-743 (1 April 2010) | doi:10.1038/nature08954. [full text]

Putting the Younger Dryas cold event into context – Broecker et al. (2010) “The Younger Dryas event is by far the best studied of the millennial-scale cold snaps of glacial time. Yet its origin remains a subject of debate. The long-held scenario that the Younger Dryas was a one-time outlier triggered by a flood of water stored in proglacial Lake Agassiz has fallen from favor due to lack of a clear geomorphic signature at the correct time and place on the landscape. The recent suggestion that the Younger Dryas was triggered by the impact of a comet has not gained traction. Instead, evidence from Chinese stalagmites suggests that, rather than being a freak occurrence, the Younger Dryas is an integral part of the deglacial sequence of events that produced the last termination on a global scale.” Wallace S. Broecker, George H. Denton, R. Lawrence Edwards, Hai Cheng, Richard B. Alley, and Aaron E. Putnam, Quaternary Science Reviews, Volume 29, Issues 9-10, May 2010, Pages 1078-1081, doi:10.1016/j.quascirev.2010.02.019.

Precise dating of abrupt shifts in the Asian Monsoon during the last deglaciation based on stalagmite data from Yamen Cave, Guizhou Province, China – Yang et al. (2010) “Based on 33 U/Th dates and 1020 oxygen isotopic data from stalagmite Y1 from Yamen Cave, Guizhou Province, China, a record of the Asian Summer Monsoon (ASM) was established. The record covers the last deglaciation and the early Holocene (from 16.2 to 7.3 ka BP) with an average oxygen isotope resolution of 9 years. The main millennial-scale deglacial events first identified in Greenland (Greenland Interstadial Events: GIS 1e through GIS 1a) and later in China are clearly present in the Y1 record. By analogy to earlier work, we refer to these as Chinese Interstadials (CIS): CIS A.1e to CIS A.1a. The onset of these events in Y1 δ18O records are nominally dated at: 14750±50, 14100±60, 13870±80, 13370±80, and 12990±80 a BP. The end of CIS A.1a or the beginning of the Younger Dryas (YD) event is nominally at 12850±50 a BP and the end of the YD dates to 11500±40 a BP. The δ18O values shift by close to 3‰ during the transition into the Bølling-Allerød (BA, the onset of CIS A.1e) and at the end of the YD. Comparisons of Y1 to previously published early Holocene records show no significant phase differences. Thus, the East Asia Monsoon and the Indian Monsoon do not appear to have been out of phase during this interval. The Y1 record confirms earlier work that suggested that solar insolation and North Atlantic climate both affect the Asian Monsoon.” Yan Yang, DaoXian Yuan, Hai Cheng, MeiLiang Zhang, JiaMing Qin, YuShi Lin, XiaoYan Zhu and R. Lawrence Edwards, SCIENCE CHINA Earth Sciences, Volume 53, Number 5, 633-641, DOI: 10.1007/s11430-010-0025-z.

Absence of geochemical evidence for an impact event at the Bølling–Allerød/Younger Dryas transition – Paquay et al. (2009) “High concentrations of iridium have been reported in terrestrial sediments dated at 12.9 ka and are interpreted to support an extraterrestrial impact event as the cause of the observed extinction in the Rancholabrean fauna, changes in the Paleoindian cultures, and the onset of the Younger Dryas cooling [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 104:16016–16021]. Here, we report platinum group element (PGE: Os, Ir, Ru, Rh, Pt, Pd), gold (Au) concentrations, and 187Os/188Os ratios in time-equivalent terrestrial, lacustrine, and marine sections to seek robust evidence of an extraterrestrial contribution. First, our results do not reproduce the previously reported elevated Ir concentrations. Second, 187Os/188Os isotopic ratios in the sediment layers investigated are similar to average crustal values, indicating the absence of a significant meteoritic Os contribution to these sediments. Third, no PGE anomalies distinct from crustal signatures are present in the marine record in either the Gulf of California (DSDP 480, Guaymas Basin) or the Cariaco Basin (ODP 1002C). Our data show no evidence of an extraterrestrial (ET)-PGE enrichment anomaly in any of the investigated depositional settings investigated across North America and in one section in Belgium. The lack of a clear ET-PGE signature in this sample suite is inconsistent with the impact of a large chondritic projectile at the Bølling–Allerød/Younger Dryas transition.” François S. Paquay, Steven Goderis, Greg Ravizza, Frank Vanhaeck, Matthew Boyd, Todd A. Surovell, Vance T. Holliday, C. Vance Haynes Jr. and Philippe Claeys, PNAS December 22, 2009 vol. 106 no. 51 21505-21510, doi: 10.1073/pnas.0908874106. [full text]

Nanodiamonds in the Younger Dryas Boundary Sediment Layer – Kennett et al. (2009) “We report abundant nanodiamonds in sediments dating to 12.9 ± 0.1 thousand calendar years before the present at multiple locations across North America. Selected area electron diffraction patterns reveal two diamond allotropes in this boundary layer but not above or below that interval. Cubic diamonds form under high temperature-pressure regimes, and n-diamonds also require extraordinary conditions, well outside the range of Earth’s typical surficial processes but common to cosmic impacts. N-diamond concentrations range from ≈10 to 3700 parts per billion by weight, comparable to amounts found in known impact layers. These diamonds provide strong evidence for Earth’s collision with a rare swarm of carbonaceous chondrites or comets at the onset of the Younger Dryas cool interval, producing multiple airbursts and possible surface impacts, with severe repercussions for plants, animals, and humans in North America.” D. J. Kennett, J. P. Kennett, A. West, C. Mercer, S. S. Que Hee, L. Bement, T. E. Bunch, M. Sellers and W. S. Wolbach, Science 2 January 2009: Vol. 323 no. 5910 p. 94, DOI: 10.1126/science.1162819. [full text]

An abrupt wind shift in western Europe at the onset of the Younger Dryas cold period – Brauer et al. (2008) “The Younger Dryas cooling 12,700 years ago is one of the most abrupt climate changes observed in Northern Hemisphere palaeoclimate records. Annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes, as the seasonal deposition responds immediately to climate, and the varve counts provide an accurate estimate of the timing of the change. Here, we present sub-annual records of varve microfacies and geochemistry from Lake Meerfelder Maar in western Germany, providing one of the best dated records of this climate transition5. Our data indicate an abrupt increase in storminess during the autumn to spring seasons, occurring from one year to the next at 12,679 yr BP, broadly coincident with other changes in this region. We suggest that this shift in wind strength represents an abrupt change in the North Atlantic westerlies towards a stronger and more zonal jet. Changes in meridional overturning circulation alone cannot fully explain the changes in European climate; we suggest the observed wind shift provides the mechanism for the strong temporal link between North Atlantic Ocean overturning circulation and European climate during deglaciation.” Achim Brauer, Gerald H. Haug, Peter Dulski, Daniel M. Sigman & Jörg F. W. Negendank, Nature Geoscience 1, 520 – 523 (2008), doi:10.1038/ngeo263. [full text]

Geochemical proxies of North American freshwater routing during the Younger Dryas cold event – Carlson et al. (2007) “The Younger Dryas cold interval represents a time when much of the Northern Hemisphere cooled from ≈12.9 to 11.5 kiloyears B.P. The cause of this event, which has long been viewed as the canonical example of abrupt climate change, was initially attributed to the routing of freshwater to the St. Lawrence River with an attendant reduction in Atlantic meridional overturning circulation. However, this mechanism has recently been questioned because current proxies and dating techniques have been unable to confirm that eastward routing with an increase in freshwater flux occurred during the Younger Dryas. Here we use new geochemical proxies (ΔMg/Ca, U/Ca, and 87Sr/86Sr) measured in planktonic foraminifera at the mouth of the St. Lawrence estuary as tracers of freshwater sources to further evaluate this question. Our proxies, combined with planktonic δ18Oseawater and δ13C, confirm that routing of runoff from western Canada to the St. Lawrence River occurred at the start of the Younger Dryas, with an attendant increase in freshwater flux of 0.06 ± 0.02 Sverdrup (1 Sverdrup = 106 m3·s−1). This base discharge increase is sufficient to have reduced Atlantic meridional overturning circulation and caused the Younger Dryas cold interval. In addition, our data indicate subsequent fluctuations in the freshwater flux to the St. Lawrence River of ≈0.06–0.12 Sverdrup, thus explaining the variability in the overturning circulation and climate during the Younger Dryas.” Anders E. Carlson, Peter U. Clark, Brian A. Haley, Gary P. Klinkhammer, Kathleen Simmons, Edward J. Brook, and Katrin J. Meissner, PNAS April 17, 2007 vol. 104 no. 16 6556-6561, doi: 10.1073/pnas.0611313104. [full text]

A deep-sea coral record of North Atlantic radiocarbon through the Younger Dryas: Evidence for intermediate water/deepwater reorganization – Eltgroth et al. (2006) “Our record of Younger Dryas intermediate-depth seawater Δ14C from North Atlantic deep-sea corals supports a link between abrupt climate change and intermediate ocean variability. Our data show that northern source intermediate water (∼1700 m) was partially replaced by 14C-depleted southern source water at the onset of the event, consistent with a reduction in the rate of North Atlantic Deep Water formation. This transition requires the existence of large, mobile gradients of Δ14C in the ocean during the Younger Dryas. The Δ14C water column profile from Keigwin (2004) provides direct evidence for the presence of one such gradient at the beginning of the Younger Dryas (∼12.9 ka), with a 100‰ offset between shallow (<∼2400 m) and deep water. Our early Younger Dryas data are consistent with this profile and also show a Δ14C inversion, with 35‰ more enriched water at ∼2400 m than at ∼1700 m. This feature is probably the result of mixing between relatively well 14C ventilated northern source water and more poorly 14C ventilated southern source intermediate water, which is slightly shallower. Over the rest of the Younger Dryas our intermediate water/deepwater coral Δ14C data gradually increase, while the atmosphere Δ14C drops. For a very brief interval at ∼12.0 ka and at the end of the Younger Dryas (11.5 ka), intermediate water Δ14C (∼1200 m) approached atmospheric Δ14C. These enriched Δ14C results suggest an enhanced initial Δ14C content of the water and demonstrate the presence of large lateral Δ14C gradients in the intermediate/deep ocean in addition to the sharp vertical shift at ∼2500 m. The transient Δ14C enrichment at ∼12.0 ka occurred in the middle of the Younger Dryas and demonstrates that there is at least one time when the intermediate/deep ocean underwent dramatic change but with much smaller effects in other paleoclimatic records.” Eltgroth, S. F., J. F. Adkins, L. F. Robinson, J. Southon, and M. Kashgarian (2006), Paleoceanography, 21, PA4207, doi:10.1029/2005PA001192. [full text]

Arctic freshwater forcing of the Younger Dryas cold reversal – Tarasov & Peltier (2005) “The last deglaciation was abruptly interrupted by a millennial-scale reversal to glacial conditions, the Younger Dryas cold event. This cold interval has been connected to a decrease in the rate of North Atlantic Deep Water formation and to a resulting weakening of the meridional overturning circulation owing to surface water freshening. In contrast, an earlier input of fresh water (meltwater pulse 1a), whose origin is disputed, apparently did not lead to a reduction of the meridional overturning circulation. Here we analyse an ensemble of simulations of the drainage chronology of the North American ice sheet in order to identify the geographical release points of freshwater forcing during deglaciation. According to the simulations with our calibrated glacial systems model, the North American ice sheet contributed about half the fresh water of meltwater pulse 1a. During the onset of the Younger Dryas, we find that the largest combined meltwater/iceberg discharge was directed into the Arctic Ocean. Given that the only drainage outlet from the Arctic Ocean was via the Fram Strait into the Greenland–Iceland–Norwegian seas, where North Atlantic Deep Water is formed today, we hypothesize that it was this Arctic freshwater flux that triggered the Younger Dryas cold reversal.” Lev Tarasov & W.R. Peltier, Nature 435, 662-665 (2 June 2005) | doi:10.1038/nature03617. [full text]

Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate changes – McManus et al. (2004) “The Atlantic meridional overturning circulation is widely believed to affect climate. Changes in ocean circulation have been inferred from records of the deep water chemical composition derived from sedimentary nutrient proxies1, but their impact on climate is difficult to assess because such reconstructions provide insufficient constraints on the rate of overturning2. Here we report measurements of 231Pa/230Th, a kinematic proxy for the meridional overturning circulation, in a sediment core from the subtropical North Atlantic Ocean. We find that the meridional overturning was nearly, or completely, eliminated during the coldest deglacial interval in the North Atlantic region, beginning with the catastrophic iceberg discharge Heinrich event H1, 17,500 yr ago, and declined sharply but briefly into the Younger Dryas cold event, about 12,700 yr ago. Following these cold events, the 231Pa/230Th record indicates that rapid accelerations of the meridional overturning circulation were concurrent with the two strongest regional warming events during deglaciation. These results confirm the significance of variations in the rate of the Atlantic meridional overturning circulation for abrupt climate changes.” J. F. McManus, R. Francois, J.-M. Gherardi, L. D. Keigwin & S. Brown-Leger, Nature 428, 834-837 (22 April 2004) | doi:10.1038/nature02494. [full text]

High concentration of atmospheric 14C during the Younger Dryas cold episode – Goslar et al. (2002) “THE various reservoirs of the global carbon cycle, with their very different residence times, are linked by a complex and evolving system of exchanges for which natural radiocarbon is the most robust tracer. Any change in the sizes of these reservoirs, or the exchange rates between them, could perturb the 14C/12C ratio of each other reservoir, and the smallest of them—the atmosphere— would be the most sensitive. In particular, high-resolution reconstructions of past atmospheric 14C/12C ratios may provide important clues to the mechanisms of abrupt climate change. Annually laminated lake sediments potentially provide an optimal record in this respect, as they preserve information about both past atmospheric 14C levels and climate changes, providing absolutely dated material beyond the range of tree-ring chronologies and, unlike corals, directly monitor 14C concentrations in atmospheric CO2. Here we report the relationship between atmospheric 14C concentration and climate changes during the Younger Dryas and early Holocene periods, derived from analyses of the annually laminated sediments of Lake Gosciaz, in central Poland. We find that atmospheric 14C concentrations during the Younger Dryas were abnormally high, which we interpret as a reduced ventilation rate of the deep ocean, most probably as a result of a decrease in intensity of the North Atlantic Deep Water formation.” Tomasz Goslar et al., Nature 377, 414 – 417 (05 October 2002); doi:10.1038/377414a0. [full text]

An Oceanic Cold Reversal During the Last Deglaciation – Stenni et al. (2001) “A detailed deuterium excess profile measured along the Dome C EPICA (European Project for Ice Coring in Antarctica) core reveals the timing and strength of the sea surface temperature changes at the source regions for Dome C precipitation. We infer that an Oceanic Cold Reversal took place in the southern Indian Ocean, 800 years after the Antarctic Cold Reversal. The temperature gradient between the oceanic moisture source and Antarctica is similar to the Dome C sodium profile during the deglaciation, illustrating the strong link between this gradient and the strength of the atmospheric circulation.” Barbara Stenni, Valerie Masson-Delmotte, Sigfus Johnsen, Jean Jouzel, Antonio Longinelli, Eric Monnin, Regine Röthlisberger and Enrico Selmo, Science 14 September 2001: Vol. 293 no. 5537 pp. 2074-2077, DOI: 10.1126/science.1059702. [full text]

The Younger Dryas cold interval as viewed from central Greenland – Alley (2000) “Greenland ice-core records provide an exceptionally clear picture of many aspects of abrupt climate changes, and particularly of those associated with the Younger Dryas event, as reviewed here. Well-preserved annual layers can be counted confidently, with only ≈1% errors for the age of the end of the Younger Dryas ≈11,500 years before present. Ice-flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty. Glaciochemical and particulate data record atmospheric-loading changes with little uncertainty introduced by changes in snow accumulation. Confident paleothermometry is provided by site-specific calibrations using ice-isotopic ratios, borehole temperatures, and gas-isotopic ratios. Near-simultaneous changes in ice-core paleoclimatic indicators of local, regional, and more-widespread climate conditions demonstrate that much of the Earth experienced abrupt climate changes synchronous with Greenland within thirty years or less. Post-Younger Dryas changes have not duplicated the size, extent and rapidity of these paleoclimatic changes.” Richard B. Alley, Quaternary Science Reviews, Volume 19, Issues 1-5, 1 January 2000, Pages 213-226, doi:10.1016/S0277-3791(99)00062-1. [full text]

Synchronous Radiocarbon and Climate Shifts During the Last Deglaciation – Hughen et al. (2000) “Radiocarbon data from the Cariaco Basin provide calibration of the carbon-14 time scale across the period of deglaciation (15,000 to 10,000 years ago) with resolution available previously only from Holocene tree rings. Reconstructed changes in atmospheric carbon-14 are larger than previously thought, with the largest change occurring simultaneously with the sudden climatic cooling of the Younger Dryas event. Carbon-14 and published beryllium-10 data together suggest that concurrent climate and carbon-14 changes were predominantly the result of abrupt shifts in deep ocean ventilation.” Konrad A. Hughen, John R. Southon, Scott J. Lehman and Jonathan T. Overpeck, Science 8 December 2000, Vol. 290 no. 5498 pp. 1951-1954, DOI: 10.1126/science.290.5498.1951. [full text]

Timing of the Antarctic cold reversal and the atmospheric CO2 increase with respect to the Younger Dryas Event – Blunier et al. (1997) “The transition from the Last Glacial to the Holocene is a key period for understanding the mechanisms of global climate change. Ice cores from the large polar ice sheets provide a wealth of information with good time resolution for this period. However, interactions between the two hemispheres can only be investigated if ice core records from Greenland and Antarctica can be synchronised accurately and reliably. The atmospheric methane concentration shows large and very fast changes during this period. These variations are well suited for a synchronisation of the age scales of ice cores from Greenland and Antarctica. Here we confirm the proposed lead of the Antarctic Cold Reversal on the Younger Dryas cold event. The Antarctic cooling precedes the Younger Dryas by at least 1.8 kyr. This suggests that northern and southern hemispheres were in anti‐phase during the Younger Dryas cold event. A further result of the synchronisation is that the long‐term glacial‐interglacial increase of atmospheric CO2 was not interrupted during the Younger Dryas event and that atmospheric CO2 changes are not necessarily dominated by changes in the North Atlantic circulation.” Blunier, T., J. Schwander, B. Stauffer, T. Stocker, A. Dällenbach, A. Indermühle, J. Tschumi, J. Chappellaz, D. Raynaud, and J.‐M. Barnola (1997), Geophys. Res. Lett., 24(21), 2683–2686, doi:10.1029/97GL02658.

The impact of glacial lake runoff on the goldthwait and champlain seas: The relationship between glacial lake agassiz runoff and the younger dryas – Rodrigues & Vilks (1994) “The freshwater flux to the North Atlantic Ocean during the last deglaciation included runoff (meltwater plus precipitation) from glacial Lake St Lawrence (ca. 11.6 ka BP), from glacial Lake Agassiz (10.9–9.9 and 9.5–8.0 ka BP) and from glacial Lake Barlow-Ojibway (9.5–8.0 ka BP). Runoff from the glacial lakes does not appear to have mixed with the deep water of the Goldthwait Sea in the Gulf of St Lawrence and was part of the surface outflow to the North Atlantic Ocean. Radiocarbon-dated invertebrate faunal assemblages show that the major impact of Lake Agassiz runoff to the North Atlantic Ocean during the 10.9 to 9.9 ka BP interval occurred after 10.5 ka BP, resulting in the freshening of the Champlain Sea. The Younger Dryas cold episode, on the other hand, began about 11.0 ka BP. The discordance between the major impact of Lake Agassiz runoff on the Champlain Sea and the beginning of the cold episode indicates that Lake Agassiz runoff did not trigger the Younger Dryas cooling. However, the runoff from glacial Lake Agassiz may have sustained the cold climate during the latter part of the Younger Dryas cold episode.” Cyril G. Rodrigues and Gustavs Vilks, Quaternary Science Reviews, Volume 13, Issues 9-10, 1994, Pages 923-944, doi:10.1016/0277-3791(94)90009-4.

Abrupt increase in Greenland snow accumulation at the end of the Younger Dryas event – Alley et al. (1993) “THE warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate, the best-known of which is the Younger Dryas event. Despite much study of the causes of this event and the mechanisms by which it ended, many questions remain unresolved. Oxygen isotope data from Greenland ice cores suggest that the Younger Dryas ended abruptly, over a period of about 50 years; dust concentrations in these cores show an even more rapid transition (20 years). This extremely short timescale places severe constraints on the mechanisms underlying the transition. But dust concentrations can reflect subtle changes in atmospheric circulation, which need not be associated with a large change in climate. Here we present results from a new Greenland ice core (GISP2) showing that snow accumulation doubled rapidly from the Younger Dryas event to the subsequent Preboreal interval, possibly in one to three years. We also find that the accumulation-rate change from the Oldest Dryas to the Bø11ing/Allerød warm period was large and abrupt. The extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the North Atlantic climate system.” R. B. Alley, D. A. Meese, C. A. Shuman, A. J. Gow, K. C. Taylor, P. M. Grootes, J. W. C. White, M. Ram, E. D. Waddington, P. A. Mayewski & G. A. Zielinski, Nature 362, 527 – 529 (08 April 1993); doi:10.1038/362527a0. [full text]

A Large Drop in Atmospheric 14C/12C and Reduced Melting in the Younger Dryas, Documented with 230Th Ages of Corals – Edwards et al. (1993) “Paired carbon-14 (14C) and thorium-230(230Th) ages were determined on fossil corals from the Huon Peninsula, Papua New Guinea. The ages were used to calibrate part of the 14C time scale and to estimate rates of sea-level rise during the last deglaciation. An abrupt offset between the 14C and 230Th ages suggests that the atmospheric 14C/12C ratio dropped by 15 percent during the latter part of and after the Younger Dryas (YD). This prominent drop coincides with greatly reduced rates of sea-level rise. Reduction of melting because of cooler conditions during the YD may have caused an increase in the rate of ocean ventilation, which caused the atmospheric 14C/12C ratio to fall. The record of sea-level rise also shows that globally averaged rates of melting were relatively high at the beginning of the YD. Thus, these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the Mississippi to the St. Lawrence River triggered the YD event.” R. Lawrence Edwards, J. Warren Beck, G. S. Burr, D. J. Donahue, J. M. A. Chappell, A. L. Bloom, E. R. M. Druffel and F. W. Taylor, Science 14 May 1993: Vol. 260 no. 5110 pp. 962-968, DOI: 10.1126/science.260.5110.962.

The younger dryas cold spell—a quest for causes – Berger (1990) “The deep-sea record shows evidence of abrupt climatic change centered on the last deglaciation (14-8 ka), and resulting in a severe cold spell between 11,000 and 10,000 years ago, known as the Younger Dryas period. The origin of this climate catastrophe is not known. Three types of possible causes must be considered: (1) running the system’s positive feedback loop in reverse (albedo, CO2, ocean circulation), (2) disturbance from internal threshold feedback (collapse of ice sheets), and (3) system-external forcing (volcanism, solar output, supernova, cosmic dust). A shutdown of the Nordic heat pump due to excessive meltwater input is one possible cause for the cold spell. This pump is driven by North Atlantic Deep-Water (NADW) production and results in advection of warm water to the Norwegian-Greenland Sea. However, NADW shutdown or slowdown occurred both before and after the Younger Dryas, while warming proceeded rapidly. Consequently, other heat pumping mechanisms may have been more important during deglaciation (e.g., import of warm surface or intermediate waters and export of cold surface water and floating ice). It was the interference with those mechanisms, then, which aided in the Big Freeze. In addition, a short-term reduction in pCO2 during the Younger Dryas appears indicated. The search for a specific cause for the Younger Dryas cold spell may be futile. In a chaotic system near its point of bifurcation, small disturbances can result in large effects, from positive feedback amplification. Every link in the feedback loop is both cause and effect. The possibility of external influence cannot be discounted: there is evidence both for increased volcanic activity and extraterrestrial disturbance at the time.” W.H. Berger, Global and Planetary Change, Volume 3, Issue 3, December 1990, Pages 219-237, doi:10.1016/0921-8181(90)90018-8.

The Younger Dryas Cool Episode in the Gulf of Mexico – Flower & Kennett (1990) “Data are presented from Orca Basin piston core EN32-PC4 in the Gulf of Mexico that confirm the existence of surface water cooling during the Younger Dry as chronozone (11–10 ka). Late glacial planktonic foraminiferal species made a reappearance between 11.4 and 9.8 ka, an episode also marked by distinctly higher oxygen isotopic values derived from the planktonic foraminifer Globigerinoides ruber. The presence of the Younger Dryas event in the gulf at 27°N demonstrates that surface water cooling extended to mid-latitude regions in the North Atlantic. The cool surface water interval is bracketed by rapid shifts in δ18O related to changes in the influx of meltwater to the Gulf of Mexico. A chronology based upon seven accelerator radiocarbon dates indicates that cooling commenced over a ∼500 year period and ended in less than 200 years. These results are among the first deep-sea sediment data documenting the climatic transitions bracketing the Younger Dryas with a rapidity observed in ice core records. A rapid decrease in δ18O values measured in the white form of Gs. ruber at 10.2 ka is explained by significant meltwater influx into the gulf and rapid increase in sea surface temperatures. Surprisingly, a similar decrease is not observed in the pink form of Gs. ruber, a summer surface water dweller in the gulf. This discrepancy may be explained by continued meltwater influx throughout the Younger Dryas during the summers only, such that there was no change in the δ18O of the pink form at the end of the episode. An additional possibility is that warming at the end of the Younger Dryas raised year-average temperatures and summer temperatures remained constant. The coincidence of rapid shifts in δ18O with the Younger Dryas strongly suggests a dynamic causal relationship and therefore supports a model for the cause of the Younger Dryas cooling based on changes in the routing of Laurentide glacial meltwater.” Flower, B. P., and J. P. Kennett (1990), Paleoceanography, 5(6), 949–961, doi:10.1029/PA005i006p00949.

Routing of meltwater from the Laurentide Ice Sheet during the Younger Dryas cold episode – Broecker et al. (1989) “ROOTH proposed that the Younger Dryas cold episode, which chilled the North Atlantic region from 11,000 to 10,000 yr BP, was initiated by a diversion of meltwater from the Mississippi drainage to the St Lawrence drainage system. The link between these events is postulated to be a turnoff, during the Younger Dryas cold episode, of the North Atlantic’s conveyor-belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the North Atlantic region. This turnoff is attributed to a reduction in surface-water salinity, and hence also in density, of the waters in the region where North Atlantic Deep Water (NADW) now forms. Here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from Orca Basin core EN32-PC4 which reveal a significant reduction in meltwater flow through the Mississippi River to the Gulf of Mexico from about 11,200 to 10,000 radiocarbon years ago. This finding is consistent with the record for Lake Agassiz which indicates that the meltwater from the southwestern margin of the Laurentide Ice Sheet was diverted to the northern Atlantic Ocean through the St Lawrence valley during the interval from ~11,000 to 10,000 years before present (yr BP).” Wallace S. Broecker, James P. Kennett, Benjamin P. Flower, James T. Teller, Sue Trumbore, Georges Bonani & Willy Wolfli, Nature 341, 318 – 321 (28 September 1989), doi:10.1038/341318a0.

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New research from last week 3/2011

Posted by Ari Jokimäki on January 24, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Reconstructing climate forcing of 1000 years

Climate forcing reconstructions for use in PMIP simulations of the last millennium (v1.0) – Schmidt et al. (2011) “Simulations of climate over the Last Millennium (850–1850 CE) have been incorporated into the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). The drivers of climate over this period are chiefly orbital, solar, volcanic, changes in land use/land cover and some variation in greenhouse gas levels. While some of these effects can be easily defined, the reconstructions of solar, volcanic and land use-related forcing are more uncertain. We describe here the approach taken in defining the scenarios used in PMIP3, document the forcing reconstructions and discuss likely implications.” Schmidt, G. A., Jungclaus, J. H., Ammann, C. M., Bard, E., Braconnot, P., Crowley, T. J., Delaygue, G., Joos, F., Krivova, N. A., Muscheler, R., Otto-Bliesner, B. L., Pongratz, J., Shindell, D. T., Solanki, S. K., Steinhilber, F., and Vieira, L. E. A., Geosci. Model Dev., 4, 33-45, doi:10.5194/gmd-4-33-2011, 2011. [full text]

Historic events of mankind don’t show in ice core CO2

Coupled climate–carbon simulations indicate minor global effects of wars and epidemics on atmospheric CO2 between AD 800 and 1850 – Pongratz et al. (2011) “Historic events such as wars and epidemics have been suggested as explanation for decreases in atmospheric CO2 reconstructed from ice cores because of their potential to take up carbon in forests regrowing on abandoned agricultural land. Here, we use a coupled climate–carbon cycle model to assess the carbon and climate effects of the Mongol invasion (∼1200 to ∼1380), the Black Death (∼1347 to ∼1400), the conquest of the Americas (∼1519 to ∼1700), and the fall of the Ming Dynasty (∼1600 to ∼1650). We calculate their impact on atmospheric CO2 including the response of the global land and ocean carbon pools. It has been hypothesized that these events have contributed to significant increases in land carbon stocks. However, we find that slow regrowth and delayed emissions from past land cover change allow for small increases of the land biosphere carbon storage only during long-lasting events. The effect of these small increases in land biosphere storage on global CO2 is reduced by the response of the global carbon pools and largely offset by concurrent emissions from the rest of the world. None of these events would therefore have affected the atmospheric CO2 concentration by more than 1 ppm. Only the Mongol invasion could have lowered global CO2, but by an amount too small to be resolved by ice cores.” Julia Pongratz, Ken Caldeira, Christian H. Reick, Martin Claussen, The Holocene January 20, 2011 0959683610386981, doi: 10.1177/0959683610386981.

Climate related soil temperature trends in Canada

Observed soil temperature trends associated with climate change in Canada – Qian et al. (2011) “Trends in soil temperature are important, but rarely reported, indicators of climate change. On the basis of the soil temperature data from 30 climate stations across Canada during 1958–2008, trends in soil temperatures at 5, 10, 20, 50, 100, and 150 cm depths were analyzed, together with atmospheric variables, such as air temperature, precipitation, and depth of snow on the ground, observed at the same locations. There was a significant positive trend with soil temperatures in spring and summer means, but not for the winter and annual means. A positive trend with time in soil temperature was detected at about two-thirds of the stations at all depths below 5 cm. A warming trend of 0.26–0.30°C/decade was consistently detected in spring (March–April–May) at all depths between 1958 and 2008. The warming trend in soil temperatures was associated with trends in air temperatures and snow cover depth over the same period. A significant decreasing trend in snow cover depth in winter and spring was associated with increasing air temperatures. The combined effects of the higher air temperature and reduced snow depth probably resulted in an enhanced increasing trend in spring soil temperatures, but no significant trends in winter soil temperatures. The thermal insulation by snow cover appeared to play an important role in the response of soil temperatures to climate change and must be accounted for in projecting future soil-related impacts of climate change.” Qian, B., E. G. Gregorich, S. Gameda, D. W. Hopkins, and X. L. Wang (2011), J. Geophys. Res., 116, D02106, doi:10.1029/2010JD015012.

2010 record melting in Greenland

The role of albedo and accumulation in the 2010 melting record in Greenland – Tedesco et al. (2011) “Analyses of remote sensing data, surface observations and output from a regional atmosphere model point to new records in 2010 for surface melt and albedo, runoff, the number of days when bare ice is exposed and surface mass balance of the Greenland ice sheet, especially over its west and southwest regions. Early melt onset in spring, triggered by above-normal near-surface air temperatures, contributed to accelerated snowpack metamorphism and premature bare ice exposure, rapidly reducing the surface albedo. Warm conditions persisted through summer, with the positive albedo feedback mechanism being a major contributor to large negative surface mass balance anomalies. Summer snowfall was below average. This helped to maintain low albedo through the 2010 melting season, which also lasted longer than usual.” M Tedesco, X Fettweis, M R van den Broeke, R S W van de Wal, C J P P Smeets, W J van de Berg, M C Serreze and J E Box, Environmental Research Letters, Volume 6, Number 1, doi: 10.1088/1748-9326/6/1/014005.

Did atomic bombs cause 1940’s cooling?

The Role of Atmospheric Nuclear Explosions on the Stagnation of Global Warming in the Mid 20th Century – Fujii (2011) “This study suggests that the cause of the stagnation in global warming in the mid 20th century was the atmospheric nuclear explosions detonated between 1945 and 1980. The estimated GST drop due to fine dust from the actual atmospheric nuclear explosions based on the published simulation results by other researchers (a single column model and Atmosphere-Ocean General Circulation Model) has served to explain the stagnation in global warming. Atmospheric nuclear explosions can be regarded as full-scale in situ tests for nuclear winter. The non-negligible amount of GST drop from the actual atmospheric explosions suggests that nuclear winter is not just a theory but has actually occurred, albeit on a small scale. The accuracy of the simulations of GST by IPCC would also be improved significantly by introducing the influence of fine dust from the actual atmospheric nuclear explosions into their climate models; thus, global warming behavior could be more accurately predicted.” Yoshiaki Fujii, Journal of Atmospheric and Solar-Terrestrial Physics, 2011, doi:10.1016/j.jastp.2011.01.005.

Increasing frequencies of heat waves attributable to human influence

Single-step attribution of increasing frequencies of very warm regional temperatures to human influence – Stott et al. (2011) “Seasonal near-surface temperatures have increased in many regions of the World. Previous work has shown that this has led to rapidly increasing frequencies of very warm Northern Hemisphere summer temperatures. Here we show, using a ‘single-step’ attribution framework, that increases in frequencies of very warm seasonal temperatures, not just in Northern Hemisphere summers but in other regions and seasons, can be directly attributed to human influence. In the June-August and September-November seasons, many of the sub-continental regions of Africa and Asia show robust attributable increase in the frequencies of anomalously warm seasonal temperatures.” Peter A. Stott, Gareth S. Jones, Nikolaos Christidis, Francis W. Zwiers, Gabriele Hegerl, Hideo Shiogama, Atmospheric Science Letters, DOI: 10.1002/asl.315.

NH cryosphere albedo feedback is larger than models predict

Radiative forcing and albedo feedback from the Northern Hemisphere cryosphere between 1979 and 2008 – Flanner et al. (2011) “The extent of snow cover1 and sea ice2 in the Northern Hemispherehas declined since 1979, coincident with hemispheric warming and indicative of a positive feedback of surface reflectivity on climate. This albedo feedback of snow on land has been quantified from observations at seasonal timescales3, 4, 5, 6, and century-scale feedback has been assessed using climate models7, 8, 9, 10. However, the total impact of the cryosphere on radiative forcing and albedo feedback has yet to be determined from measurements. Here we assess the influence of the Northern Hemisphere cryosphere on Earth’s radiation budget at the top of the atmosphere—termed cryosphere radiative forcing—by synthesizing a variety of remote sensing and field measurements. We estimate mean Northern Hemisphere forcing at −4.6 to −2.2 W m−2, with a peak in May of −9.0±2.7 W m−2. We find that cyrospheric cooling declined by 0.45 W m−2 from 1979 to 2008, with nearly equal contributions from changes in land snow cover and sea ice. On the basis of these observations, we conclude that the albedo feedback from the Northern Hemisphere cryosphere falls between 0.3 and 1.1 W m−2 K−1, substantially larger than comparable estimates obtained from 18 climate models.” M. G. Flanner, K. M. Shell, M. Barlage, D. K. Perovich & M. A. Tschudi, Nature Geoscience, 2011, DOI: doi:10.1038/ngeo1062.

GHG warming detected in Europe since 17th century

Influence of human and natural forcing on European seasonal temperatures – Hegerl et al. (2011) “It is the regional and seasonal expression of climate change that determines the effect of greenhouse warming on ecosystemsand society. Whereas anthropogenic influences on European temperatures have been detected over the twentieth century, it has been suggested that the impact of external influences on European temperatures before 1900 is negligible. Here we use reconstructions of seasonal European land temperature5, 6 and simulations with three global climate models to show that external influences on climate—such as the concentrations of stratospheric volcanic aerosols or greenhouse gases, other anthropogenic effects and possibly changes in total solar irradiance—have had a discernible influence on European temperatures throughout the past five centuries. In particular, we find that external forcing contributes significantly (p<5%) to the reconstructed long-term variability of winter and spring temperatures and that it is responsible for a best guess of 75% of the observed winter warming since the late seventeenth century. This warming is largely attributable to greenhouse-gas forcing. Summer temperatures show detectable (p<5%) interdecadal variations in response to external forcing before 1900 only. Finally, throughout the record we detect highly significant summer cooling and significant winter warming following volcanic eruptions." Gabriele Hegerl, Juerg Luterbacher, Fidel González-Rouco, Simon F. B. Tett, Thomas Crowley & Elena Xoplaki, Nature Geoscience, 2011, DOI: doi:10.1038/ngeo1057.

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New research from last week 2/2011

Posted by Ari Jokimäki on January 17, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Cessation of emissions would cause increasing temperatures

Climate commitment in an uncertain world – Armour & Doe (2011) “Climate commitment—the warming that would still occur given no further human influence—is a fundamental metric for both science and policy. It informs us of the minimum climate change we face and, moreover, depends only on our knowledge of the natural climate system. Studies of the climate commitment due to CO2 find that global temperature would remain near current levels, or even decrease slightly, in the millennium following the cessation of emissions. However, this result overlooks the important role of the non-CO2 greenhouse gases and aerosols. This paper shows that global energetics require an immediate and significant warming following the cessation of emissions as aerosols are quickly washed from the atmosphere, and the large uncertainty in current aerosol radiative forcing implies a large uncertainty in the climate commitment. Fundamental constraints preclude Earth returning to pre-industrial temperatures for the indefinite future. These same constraints mean that observations are currently unable to eliminate the possibility that we are already beyond the point where the ultimate warming will exceed dangerous levels. Models produce a narrower range of climate commitment, but undersample observed forcing constraints.” Armour, K. C., and G. H. Roe (2011), Geophys. Res. Lett., 38, L01707, doi:10.1029/2010GL045850. [full text]

Iran’s temperatures have been increasing since the 1970s

Testing for long-term trends in climatic variables in Iran – Tabari et al. (2011) “Analysis of long-term climatic data sets is currently of unprecedented interest to the scientific community. In this study, the trends of the annual maximum (Tmax), minimum (Tmin) and mean (Tmean) air temperatures and precipitation (P) time series were examined in the west, south and southwest of Iran for the period 1966–2005. The magnitude of the climatic trends was derived from the slopes of the regression lines, and the statistical significance was determined by means of the Mann-Kendall, Mann-Whitney and Mann-Kendall rank statistic tests. Pre-whitening was used to eliminate the influence of serial correlation on the Mann-Kendall test. The results showed a warming trend in annual Tmean, Tmax and Tmin at the majority of the stations which mostly began in the 1970 s. On average, the magnitudes of the significant positive trends in annual Tmean, Tmax and Tmin were (+)0.412, (+)0.452 and (+)0.493 °C per decade, respectively. However, the variations of the P series were not uniform over the region and there were various patterns (increasing and decreasing trends).” Hossein Tabari, Behzad Shifteh Somee and Mehdi Rezaeian Zadeh, Atmospheric Research, doi:10.1016/j.atmosres.2011.01.005.

Is the East Antarctic ice sheet stable?

Is the East Antarctic ice sheet stable? – Pingree et al. (2011) “The Greenland and East and West Antarctic ice sheets are assessed as being the source of ice that produced an Eemian sea level 6 m higher than present sea level. The most probable source is total collapse of the West Antarctic Ice Sheet accompanied by partial collapse of the adjacent sector of the East Antarctic Ice Sheet in direct contact with the West Antarctic Ice Sheet. This conclusion is reached by applying a simple formula relating the “floating fraction” of ice along flowlines to ice height above the bed. Increasing the floating fraction lowered ice elevations enough to contribute up to 4.7 m to global sea level. Adding 3.3 m resulting from total collapse of the West Antarctic Ice Sheet accounts for the higher Eemian sea level. Partial gravitational collapse that produced the present ice drainage system of Amery Ice Shelf contributes 2.3 m to global sea level. These results cast doubt on the presumed stability of the East Antarctic Ice Sheet, but destabilizing mechanisms remain largely unknown. Possibilities include glacial surges and marine instabilities at the respective head and foot of ice streams.” Katherine Pingree, Max Lurie and Terence Hughes, Quaternary Research, doi:10.1016/j.yqres.2010.12.001.

Future changes in Tibetan Plateau forests

Assessing potential impacts of climatic change on subalpine forests on the eastern Tibetan Plateau – Xiaodan et al. (2011) “Forest gap models have been used widely in the study of forest dynamics, including predicting long-term succession patterns and assessing the potential impacts of climate change on forest structure and composition. However, little effort is devoted to predict forest dynamics in the high elevation areas, although they have the sensitive response to global climate change. In the present study, based on a modified height-diameter function, we developed a new version (FAREAST-GFSM) of the forest patch model, FAREAST for simulating the changes of subalpine forests. The observed data from the Gongga Mt. Alpine Station were also used to test model precision. With the improved performance of FAREAST-GFSM, we explored the impact of three warming scenarios on subalpine forest on the eastern Tibetan plateau within a 100-year period. The study result indicates that the effects of climate change were evident on subalpine forests in the high elevation areas. The response of different species to the warming climate might eventually transform the subalpine Abies fabric forest into Betula utilis forest similar to that which is now widely distributed in the eastern Tibetan Plateau mountainous areas with the relatively lower elevation. Subalpine forests could move to higher and colder areas, which are currently tundra.” Wang Xiaodan, Cheng Genwei and Zhong Xianghao, Climatic Change, DOI: 10.1007/s10584-010-0008-2.

Total solar irradiance value for solar minimum

A new, lower value of total solar irradiance: Evidence and climate significance – Kopp & Lean (2011) “The most accurate value of total solar irradiance during the 2008 solar minimum period is 1360.8 ± 0.5 W m−2 according to measurements from the Total Irradiance Monitor (TIM) on NASA’s Solar Radiation and Climate Experiment (SORCE) and a series of new radiometric laboratory tests. This value is significantly lower than the canonical value of 1365.4 ± 1.3 W m−2 established in the 1990s, which energy balance calculations and climate models currently use. Scattered light is a primary cause of the higher irradiance values measured by the earlier generation of solar radiometers in which the precision aperture defining the measured solar beam is located behind a larger, view-limiting aperture. In the TIM, the opposite order of these apertures precludes this spurious signal by limiting the light entering the instrument. We assess the accuracy and stability of irradiance measurements made since 1978 and the implications of instrument uncertainties and instabilities for climate research in comparison with the new TIM data. TIM’s lower solar irradiance value is not a change in the Sun’s output, whose variations it detects with stability comparable or superior to prior measurements; instead, its significance is in advancing the capability of monitoring solar irradiance variations on climate-relevant time scales and in improving estimates of Earth energy balance, which the Sun initiates.” Greg Kopp and Judith L. Lean, GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L01706, 7 PP., 2011, doi:10.1029/2010GL045777.

Solar activity cycles in tree rings of Brazil

Sun-earth relationship inferred by tree growth rings in conifers from Severiano De Almeida, Southern Brazil – Prestes et al. (2011) “This study of Sun-Earth relationships is based on tree growth rings analysis of araucarias (Araucaria angustifolia) collected at Severiano de Almeida (RS) Brazil. A chronology of 359 years was obtained, and the classical method of spectral analysis by iterative regression and wavelet method was applied to find periodicities and trends contained in the tree growth. The analysis of the dendrochronological series indicates representative periods of solar activity of 11 (Schwabe cycle), 22 (Hale cycle), and 80 (Gleissberg cycle) years. The result shows the possible influence of the solar activity on tree growth in last the 350 years. Periods of 2 to 7 years were also found and could represent a response of the trees to local climatic conditions. Good agreement between the time series of tree growth rings and the 11 year solar cycle was found during the maximum solar activity periods.” A. Prestes, N.R. Rigozo, D.J.R. Nordemann, C.M. Wrasse, M.P. Souza Echer, E. Echer, M.B. da Rosa and P.H. Rampelotto, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2010.12.014.

Difficulty of finding cloud-free pixel with MODIS

Global analysis of cloud field coverage and radiative properties, using morphological methods and MODIS observations – Bar-Or et al. (2011) “The recently recognized continuous transition zone between detectable clouds and cloud-free atmosphere (“the twilight zone”) is affected by undetectable clouds and humidified aerosol. In this study, we suggest to distinguish cloud fields (including the detectable clouds and the surrounding twilight zone) from cloud-free areas, which are not affected by clouds. For this classification, a robust and simple-to-implement cloud field masking algorithm which uses only the spatial distribution of clouds, is presented in detail. A global analysis, estimating Earth’s cloud field coverage (50° S–50° N) for 28 July 2008, using the Moderate Resolution Imaging Spectroradiometer (MODIS) data, finds that while the declared cloud fraction is 51%, the global cloud field coverage reaches 88%. The results reveal the low likelihood for finding a cloud-free pixel and suggest that this likelihood may decrease as the pixel size becomes larger. A global latitudinal analysis of cloud fields finds that unlike oceans, which are more uniformly covered by cloud fields, land areas located under the subsidence zones of the Hadley cell (the desert belts), contain proper areas for investigating cloud-free atmosphere as there is 40–80% probability to detect clear sky over them. Usually these golden-pixels, with higher likelihood to be free of clouds, are over deserts. Independent global statistical analysis, using MODIS aerosol and cloud products, reveals a sharp exponential decay of the global mean aerosol optical depth (AOD) as a function of the distance from the nearest detectable cloud, both above ocean and land. Similar statistical analysis finds an exponential growth of mean aerosol fine-mode fraction (FMF) over oceans when the distance from the nearest cloud increases. A 30 km scale break clearly appears in several analyses here, suggesting this is a typical natural scale of cloud fields. This work shows different microphysical and optical properties of cloud fields, urging to separately investigate cloud fields and cloud-free atmosphere in future climate research.” Bar-Or, R. Z., Altaratz, O., and Koren, I., Atmos. Chem. Phys., 11, 191-200, doi:10.5194/acp-11-191-2011, 2011. [full text]

Differences in mountain flora survival across Europe

21st century climate change threatens mountain flora unequally across Europe – Engler et al. (2011) “Continental-scale assessments of 21st century global impacts of climate change on biodiversity have forecasted range contractions for many species. These coarse resolution studies are however of limited relevance for projecting risks to biodiversity in mountain systems, where pronounced microclimatic variation could allow species to persist locally, and are ill-suited for assessment of species-specific threat in particular regions. Here, we assess the impacts of climate change on 2632 plant species across all major European mountain ranges, using high-resolution (ca. 100 m) species samples and data expressing four future climate scenarios. Projected habitat loss is greater for species distributed at higher elevations; depending on the climate scenario, we find 36–55% of alpine species, 31–51% of subalpine species and 19–46% of montane species lose more than 80% of their suitable habitat by 2070–2100. While our high-resolution analyses consistently indicate marked levels of threat to cold-adapted mountain florae across Europe, they also reveal unequal distribution of this threat across the various mountain ranges. Impacts on florae from regions projected to undergo increased warming accompanied by decreased precipitation, such as the Pyrenees and the Eastern Austrian Alps, will likely be greater than on florae in regions where the increase in temperature is less pronounced and rainfall increases concomitantly, such as in the Norwegian Scandes and the Scottish Highlands. This suggests that change in precipitation, not only warming, plays an important role in determining the potential impacts of climate change on vegetation.” Robin Engler, Christophe F. Randin, Wilfried Thuiller, Stefan Dullinger, Niklaus E. Zimmermann, Miguel B. Araújo, Peter B. Pearman, Gwenaëlle Le Lay, Christian Piedallu, Cécile H. Albert, Philippe Choler, Gheorghe Coldea, Xavier De Lamo, Thomas Dirnböck, Jean-Claude Gégout, Daniel Gómez-García, John-Arvid Grytnes, Einar Heegaard, Fride Høistad, David Nogués-Bravo, Signe Normand, Mihai Puşcaş, Maria-Teresa Sebastiá, Angela Stanisci, Jean-Paul Theurillat, Mandar R. Trivedi, Pascal Vittoz, Antoine Guisan, Global Change Biology, DOI: 10.1111/j.1365-2486.2010.02393.x.

Growing season timing changes in Northern Hemisphere

Phenology shifts at start vs. end of growing season in temperate vegetation over the Northern Hemisphere for the period 1982–2008 – Jeong et al. (2011) “Changes in vegetative growing seasons are dominant indicators of the dynamic response of ecosystems to climate change. Therefore, knowledge of growing seasons over the past decades is essential to predict ecosystem changes. In this study, the long-term changes in the growing seasons of temperate vegetation over the Northern Hemisphere were examined by analyzing satellite-measured normalized difference vegetation index and reanalysis temperature during 1982–2008. Results showed that the length of the growing season (LOS) increased over the analysis period; however, the role of changes at the start of the growing season (SOS) and at the end of the growing season (EOS) differed depending on the time period. On a hemispheric scale, SOS advanced by 5.2 days in the early period (1982–1999) but advanced by only 0.2 days in the later period (2000–2008). EOS was delayed by 4.3 days in the early period, and it was further delayed by another 2.3 days in the later period. The difference between SOS and EOS in the later period was due to less warming during the preseason (Jan-Apr) before SOS compared to the magnitude of warming in the preseason (June-Sept) before EOS. At a regional scale, delayed EOS in later periods was shown. In North America, EOS was delayed by 8.1 days in the early period and delayed by another 1.3 days in the later period. In Europe, the delayed EOS by 8.2 days was more significant than the advanced SOS by 3.2 days in the later period. However, in East Asia, the overall increase in LOS during the early period was weakened in the later period. Admitting regional heterogeneity, changes in hemispheric features suggest that the longer-lasting vegetation growth in recent decades can be attributed to extended leaf senescence in autumn rather than earlier spring leaf-out.” Su-Jong Jeong, Chang-Hoi Ho, Hyeon-Ju Gim, Molly E. Brown, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02397.x.

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Papers on rainfall, flooding and droughts in Australia

Posted by Ari Jokimäki on January 12, 2011

The flooding in Australia has been in the news in last few days. The fellow Australian bloggers have also wrote about the event:

John Cook of Skeptical Science lives in Brisbane which is being flooded currently. The Latest report from John says:

I’m happy to say the Cook family is safe and dry – we happen to be located in a relatively elevated area (not by design – extreme flooding was not even on my radar when we moved into the area).

I hope that situation remains that way – that John and his family stay safe.

Papers on rainfall, flooding and droughts in Australia

This is a list of papers on flooding and droughts in Australia. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Assessing trends in observed and modelled climate extremes over Australia in relation to future projections – Alexander & Arblaster (2009) “Multiple simulations from nine globally coupled climate models were assessed for their ability to reproduce observed trends in a set of indices representing temperature and precipitation extremes over Australia. Observed trends over the period 1957–1999 were compared with individual and multi-modelled trends calculated over the same period. When averaged across Australia, the magnitude of trends and interannual variability of temperature extremes were well simulated by most models, particularly for the index for warm nights. The majority of models also reproduced the correct sign of trend for precipitation extremes although there was much more variation between the individual model runs. A bootstrapping technique was used to calculate uncertainty estimates and also to verify that most model runs produce plausible trends when averaged over Australia. Although very few showed significant skill at reproducing the observed spatial pattern of trends, a pattern correlation measure showed that spatial noise could not be ruled out as dominating these patterns. Two of the models with output from different forcings showed that the observed trends over Australia for one of the temperature indices was consistent with an anthropogenic response, but was inconsistent with natural-only forcings. Future projected changes in extremes using three emissions scenarios were also analysed. Australia shows a shift towards warming of temperature extremes, particularly a significant increase in the number of warm nights and heat waves with much longer dry spells interspersed with periods of increased extreme precipitation, irrespective of the scenario used.” Lisa V. Alexander and Julie M. Arblaster, International Journal of Climatology, Special Issue: Climate Extremes: progress and future directions, Volume 29, Issue 3, pages 417–435, 15 March 2009, DOI: 10.1002/joc.1730. [full text]

Association between Australian rainfall and the Southern Annular Mode – Meneghini et al. (2007) “In this study, we explore the relationships between seasonal Australian rainfall and the Southern Annular Mode (SAM). We produce two seasonal indices of the SAM: the Antarctic Oscillation Index (AOI), and an Australian regional version (AOIR) using ERA-40 mean sea-level pressure (MSLP) reanalysis data. The seasonal rainfall data are based on gridded monthly rainfall provided by the Australian Bureau of Meteorology. For the period 1958–2002 a significant inverse relationship is found between the SAM and rainfall in southern Australia, while a significant in-phase relationship is found between the SAM and rainfall in northern Australia. Furthermore, widespread significant inverse relationships in southern Australia are only observed in winter, and only with the AOIR. The AOIR accounts for more of the winter rainfall variability in southwest Western Australia, southern South Australia, western and southern Victoria, and western Tasmania than the Southern Oscillation Index. Overall, our results suggest that changes in the SAM may be partly responsible for the current decline in winter rainfall in southern South Australia, Victoria, and Tasmania, but not the long-term decline in southwest Western Australian winter rainfall.” Belinda Meneghini, Ian Simmonds, Ian N. Smith, International Journal of Climatology, Volume 27, Issue 1, pages 109–121, January 2007, DOI: 10.1002/joc.1370. [full text]

An assessment of recent trends in Australian rainfall – Smith (2004) “Trends in Australian rainfall over the period 1901 to 2002 are analysed with the aim of evaluating and assessing long-term trends. In particular, this study examines long-term trends in Australian rainfall with the aim of identifying any continental-scale patterns that could be described as `unusual’. All-Australia annual average rainfall and all-Australia average decile time series indicate a positive long-term trend over the full period. Trend maps indicate that much of this trend is the result of increases in summer half-year rainfall over western, northern and central Australia that have occurred over the latter part of the record 1952-2002. While significant negative trends in winter half-year rainfall over southwest Western Australia are evident, there is little evidence that they are part of any continental-scale trends, at least not on 100 or 50-year time-scales. Empirical Orthogonal Teleconnection patterns (EOTs) of annual rainfall provide a means for delineating independent spatial modes. These indicate that much of the variance in all-Australian rainfall can be attributed to the first two modes that cover much of central eastern Australia and central western Australia. In addition, the pattern of positive trends comprises at least two modes, which, being linearly independent, indicate that the large-scale pattern of increases is itself unusual in a historical context.” Smith, I., Australian Meteorological Magazine, Vol. 53, no. 3, pp. 163-173. Sep 2004. [full text]

Climate change and Australia: Trends, projections and impacts – Hughes (2003) “This review summarizes recent research in Australia on: (i) climate and geophysical trends over the last few decades; (ii) projections for climate change in the 21st century; (iii) predicted impacts from modelling studies on particular ecosystems and native species; and (iv) ecological effects that have apparently occurred as a response to recent warming. Consistent with global trends, Australia has warmed ∼0.8°C over the last century with minimum temperatures warming faster than maxima. There have been significant regional trends in rainfall with the northern, eastern and southern parts of the continent receiving greater rainfall and the western region receiving less. Higher rainfall has been associated with an increase in the number of rain days and heavy rainfall events. Sea surface temperatures on the Great Barrier Reef have increased and are associated with an increase in the frequency and severity of coral bleaching and mortality. Sea level rises in Australia have been regionally variable, and considerably less than the global average. Snow cover and duration have declined significantly at some sites in the Snowy Mountains. CSIRO projections for future climatic changes indicate increases in annual average temperatures of 0.4-2.0°C by 2030 (relative to 1990) and 1.0-6.0°C by 2070. Considerable uncertainty remains as to future changes in rainfall, El Nino Southern Oscillation events and tropical cyclone activity. Overall increases in potential evaporation over much of the continent are predicted as well as continued reductions in the extent and duration of snow cover. Future changes in temperature and rainfall are predicted to have significant impacts on most vegetation types that have been modelled to date, although the interactive effect of continuing increases in atmospheric CO2 has not been incorporated into most modelling studies. Elevated CO2 will most likely mitigate some of the impacts of climate change by reducing water stress. Future impacts on particular ecosystems include increased forest growth, alterations in competitive regimes between C3 and C4 grasses, increasing encroachment of woody shrubs into arid and semiarid rangelands, continued incursion of mangrove communities into freshwater wetlands, increasing frequency of coral bleaching, and establishment of woody species at increasingly higher elevations in the alpine zone. Modelling of potential impacts on specific Australian taxa using bioclimatic analysis programs such as BIOCLIM consistently predicts contraction and/or fragmentation of species’ current ranges. The bioclimates of some species of plants and vertebrates are predicted to disappear entirely with as little as 0.5-1.0°C of warming. Australia lacks the long-term datasets and tradition of phenological monitoring that have allowed the detection of climate-change-related trends in the Northern Hemisphere. Long-term changes in Australian vegetation can be mostly attributed to alterations in fire regimes, clearing and grazing, but some trends, such as encroachment of rainforest into eucalypt woodlands, and establishment of trees in subalpine meadows probably have a climatic component. Shifts in species distributions toward the south (bats, birds), upward in elevation (alpine mammals) or along changing rainfall contours (birds, semiarid reptiles), have recently been documented and offer circumstantial evidence that temperature and rainfall trends are already affecting geographic ranges. Future research directions suggested include giving more emphasis to the study of climatic impacts and understanding the factors that control species distributions, incorporating the effects of elevated CO2 into climatic modelling for vegetation and selecting suitable species as indicators of climate-induced change.” Lesley Hughes, Austral Ecology, Volume 28, Issue 4, pages 423–443, August 2003, DOI: 10.1111/j.1442-9993.2003.tb00266.x. [full text]

Trends in extreme rainfall indices for an updated high quality data set for Australia, 1910–1998 – Haylock & Nicholls (2000) “Daily rainfall was analysed at 91 high quality stations over eastern and southwestern Australia to determine if extreme rainfall had changed between 1910 and 1998. Three indices of extreme rainfall were examined: the number of events above an extreme threshold (extreme frequency); the average intensity of rainfall from extreme events (extreme intensity); and the proportion of total rainfall from extreme events (extreme percent). Several problems are discussed associated with designing such indices under a climate with significant trends in the number of raindays. Three different methods are used for calculating the extreme intensity and extreme percent indices to account for such trends in raindays. A separate analysis was carried out for four separate regions with significant results including a decrease in the extreme frequency and extreme intensity in southwest Western Australia and an increase in the extreme percent in eastern Australia. Trends in the extreme intensity and extreme percent are largely dependent on the method used to calculate the index. Total rainfall is strongly correlated with the extreme frequency and extreme intensity indices, suggesting that extreme events are more frequent and intense during years with high rainfall. Due to an increase in the number of raindays during such years, the proportional contribution from extreme events to the total rainfall depends on the method used to calculate this index.” Malcolm Haylock, Neville Nicholls, International Journal of Climatology, Volume 20, Issue 13, pages 1533–1541, 15 November 2000, DOI: 10.1002/1097-0088(20001115)20:133.0.CO;2-J. [full text]

Waterfalls, floods and climate change: evidence from tropical Australia – Nott & Price (1999) “Sediments preserved at the base of rare types of waterfalls provide records of terrestrial floods to 30 kyr or more, being approximately 6–10 times longer than that usually obtained from the traditional slackwater method. These coarse-grained sand deposits form ridges and levees adjacent to plunge pools at the foot of unindented escarpments and within gorge overflow bedrock channel systems. The extension of palaeoflood records into the Late Pleistocene allows comparisons to be made between periods of extreme floods and dramatically different climatic regimes. Our results highlight that the last 30 kyr were dominated by alternating periods of extreme and relatively low magnitude floods that correspond to particular climatic regimes. Recent predictions from Global Climate Models suggest that tropical regions will experience dramatic increases in the frequency and magnitude of extreme floods under a future altered climate. Plunge-pool palaeoflood records can be used to at least partially test such predictions by determining whether similar previous climate/flood associations have occurred within a region.” Jonathan Nott and David Price, 1999, Earth and Planetary Science Letters, Volume 171, Issue 2, 30 August 1999, Pages 267-276, doi:10.1016/S0012-821X(99)00152-1.

Australian rainfall changes, 1910-1995 – Hennessy et al. (1999) “Annual and seasonal trends in heavy daily rainfall, total rainfall and the number of rain days were calculated for the whole of Australia and each State/Territory from 1910 to 1995, using high-quality daily data from 379 stations. Trend significance was determined using the Kendall-tau test and trend magnitudes were computed from linear regression. While many statistically significant trends were found, non-significant trends judged to be of special interest are noted. From 1910-1995, annual total rainfall has undergone secular changes with a significant 14 per cent increase in Victoria and non-significant increases of 15-18 per cent in New South Wales (NSW), the Northern Territory (NT) and South Australia (SA). When analysed seasonally, non-significant changes of 10-40 per cent were found in some States. Heavy rainfall indices were defined as the 99th and 95th percentiles (the highest and 5th highest daily amounts, respectively, in each three-month season). Australian areal-mean heavy rainfall has not changed significantly in any season. However, on a regional basis significant increases in heavy rainfall emerged in SA in summer and NSW in autumn, while significant decreases occurred in southwest Western Australia (SWWA) in winter. Important non-significant increases of 10-45 per cent were also found in some States. There has been a significant 10 per cent rise in the annual Australian-average number of rain days. Significant increases of almost 20 per cent were found in the NT and NSW despite a significant 10 per cent decline in SWWA. Regionally, significant increases of 20-50 per cent have occurred in some States, with large changes in the frequency of light rainfall. Strong correlations exist between interannual variations in temperature, total rainfall, heavy rainfall and the number of rain days. Increases in Australian rainfall since 1910 are generally linked to an increase in heavy rainfall and the number of rain days. ENSO variability is partly responsible, as is enhanced monsoon activity in the 1970s and changes in other large-scale circulation features. Decreased rainfall in southwest WA is also linked to circulation changes.” Hennessy, KJ | Suppiah, R | Page, CM, Australian Meteorological Magazine, Vol. 48, no. 1, pp. 1-13. Mar 1999. [full text]

Annual climate summary 1998: Australia’s warmest year on record – Collins & Della-Marta (1999) “A high quality dataset developed to monitor long-term temperature trends in Australia has been updated. The annual mean time-series indicates that in 1998 Australia recorded its highest ever annual mean temperature since the start of the high-quality record in 1910. The largest contribution to the record temperature came from much higher than usual minimum temperatures throughout the northern half of the continent. High-quality rainfall and cloud cover datasets have also been updated. Greater than average cloud cover during 1998 contributed to milder overnight temperatures and generally wetter than average conditions through most of the country. The result of a warm, wet and cloudy year during 1998 is unusual in the instrumental record for Australia as studies in interannual climate variations indicate that mean temperature is generally out of phase with both rainfall and cloud cover. However, these apparent inconsistencies support the suggestion made by previous studies that the relationship between Australian temperature and rainfall changed abruptly during the early 1970s.” Collins D. A. & Della-Marta P. M., 1999, Aust. Meteorol. Mag. 48, 273–83. [full text]

Trends in total rainfall, heavy rain events and number of dry days in Australia, 1910–1990 – Suppiah & Hennessy (1998) “Trends in heavy rainfall, total rainfall and number of dry days in Australia have been analysed using daily rainfall records at 125 stations. Summer and winter halves of the year were considered separately for the period 1910–1990. The summer half-year is defined as November–April, while the winter-half is May–October. Heavy rainfall is defined as the 90th and 95th percentiles of daily rainfall in each half-year. The magnitude of trends was derived from linear regression while statistical significance was determined by Kendall-Tau and field significance tests. Increasing trends in heavy rainfall and total rainfall have occurred during the summer half-year, but only 10–20% of stations have statistically significant trends. During the winter half-year, heavy rainfall and total rainfall have also increased, except in far southwest Western Australia and inland Queensland. There has been a reduction in the number of dry days in both halves of the year, except in far southwest Western Australia and at a few stations in eastern Australia where there has been an increase in the number of dry days in the winter half-year. Changes in the number of dry days were statistically significant at over 50% of stations. Hence there are regions showing coherent increases and decreases in rainfall which may be due to systematic changes in climate during the last century. Trends were averaged over three broad regions with adequate station coverage. There has been a general decrease in dry days with an increase in total and heavy rainfall intensity in the northeast and southeast, and a decrease in total and heavy rainfall in the southwest. These rainfall changes are related to changes in other climate variables such as temperature and cloud cover in Australia.” Ramasamy Suppiah, Kevin J. Hennessy, International Journal of Climatology, Volume 18, Issue 10, pages 1141–1164, August 1998, DOI: 10.1002/(SICI)1097-0088(199808)18:103.0.CO;2-P.

An extended high-quality historical rainfall dataset for Australia – Lavery et al. (1997) “Lavery et al. (1992) identified 191 high-quality long-term rainfall records after an exhaustive search of documentation on Australian rainfall sites, coupled with statistical tests. This dataset had a relatively poor spatial distribution and so high-quality composited rainfall records and some records of shorter duration now have been added. The final dataset of 379 high-quality rainfall records (341 of which commence no later than 1910) can reliably monitor rainfall trends for most of Australia. The techniques used to composite the records, and the resulting dataset, are described. With this enhanced spatial coverage it is feasible to perform an areal averaging of precipitation for Australia. A time-series of all-Australian annual rainfall since 1890 has been constructed. Time-series were also constructed of northern summer and southern winter Australian rainfall. In all time-series the El Niño/Southern Oscillation signal is clearly evident.” Lavery, B., Joung, G. and Nicholls, N., 1997, Aust. Meteorol. Mag. 46, 27–38. [full text]

Implications of climate change due to the enhanced greenhouse effect on floods and droughts in Australia – Whetton et al. (1993) “Potential impacts of climate change on heavy rainfall events and flooding in the Australian region are explored using the results of a general circulation model (GCM) run in an equilibrium enhanced greenhouse experiment. In the doubled CO2 simulation, the model simulates an increase in the frequency of high-rainfall events and a decrease in the frequency of low-rainfall events. This result applies over most of Australia, is statistically more significant than simulated changes in total rainfall, and is supported by theoretical considerations. We show that this result implies decreased return periods for heavy rainfall events. The further implication is that flooding could increase, although we discuss here the many difficulties associated with assessing in quantitative terms the significance of the modelling results for the real world. The second part of the paper assesses the implications of climate change for drought occurrence in Australia. This is undertaken using an off-line soil water balance model driven by observed time series of rainfall and potential evaporation to determine the sensitivity of the soil water regime to changes in rainfall and temperature, and hence potential evaporation. Potential impacts are assessed at nine sites, representing a range of climate regimes and possible climate futures, by linking this sensitivity analysis with scenarios of regional climate change, derived from analysis of enhanced greenhouse experiment results from five GCMs. Results indicate that significant drying may be limited to the south of Australia. However, because the direction of change in terms of the soil water regime is uncertain at all sites and for all seasons, there is no basis for statements about how drought potential may change.” P. H. Whetton, A. M. Fowler, M. R. Haylock and A. B. Pittock, 1993, Climatic Change, Volume 25, Numbers 3-4, 289-317, DOI: 10.1007/BF01098378.

Australian rainfall trends during the twentieth century – Nicholls & Lavery (1992) “A set of high-quality rainfall records is used to examine rainfall trends over Australia during the twentieth century. The 191 stations used have been selected by an exhaustive search of documentation regarding instrumentation, observational practices, site relocations, and exposure. Statistical tests of the reliability of observing practices also have been applied in the selection process, as well as tests to detect inhomogeneities. The data set used is the most reliable available for monitoring rainfall trends during the twentieth century. The data have been clustered objectively into groups exhibiting similar variations in annual rainfall. A subset of 10 stations (one for each cluster) suitable for long-term monitoring of rainfall trends is selected. The trends in annual, winter, and summer rainfall are exhibited. The study confirms trends noted in earlier studies. Summer rainfall over much of eastern Australia increased abruptly around 1950. In the south-west of the continent most stations recorded a smoother trend to lower winter rainfall, although there is a small area with increased rainfall. The identification of these trends in this study indicates that they are not the result of unreliable observations or to doubtful compositing of stations into groups. These trends have now continued for some decades after their initial observation. It is possible, however, that the twentieth century trends simply reflect a return to conditions of the late nineteenth century, rather than a trend that could be unambiguously attributed to an enhanced ‘greenhouse effect’.” Neville Nicholls, Beth Lavery, International Journal of Climatology, Volume 12, Issue 2, pages 153–163, March 1992, DOI: 10.1002/joc.3370120204.

A historical rainfall data set for Australia – Lavery et al. (1992) “An exhaustive search of documentation regarding observational practices, instrumentation, site relocations and exposure of instruments has been conducted for Australian rainfall stations. The aim has been to identify high quality long-term rainfall stations which could be used to monitor and assess climate changes. Statistical tests were also employed in the selection process to determine the reliability of observing practices and to check for inhomogeneities in the data. The data set is the most reliable available for monitoring rainfall trends in Australia during the twentieth century. These data will be utilised in further studies as references for testing the reliability of records from neighbouring stations, and in the process of modifying such records. They can confidently be used in climate studies requiring data without spurious trends or inhomogeneities.” Lavery, B., Kariko, A. and Nicholls, N., 1992, Aust. Meteorol. Mag. 40, 33–39. [full text]

Analysis of Australian rainfall data with respect to climate variability and change – Srikanthan & Stewart (1991) “Predictions by general circulation models of changes in rainfall rates over Australia under the double carbon dioxide scenario are conflicting. As it will be some time before the quality of these predictions improves, our best indicator of rainfall variability and change is the analysis of the behaviour of recorded data over time. This paper presents the results of statistical analysis of annual and monthly rainfall data for 69 rainfall stations around Australia. The annual and monthly time-series are analysed for trend and jump in the mean. Graphical plots of the rainfall data indicate low frequency variations but there is no significant or conclusive evidence of climate change impacts within the analysed annual rainfall records. However, the data from a third of the stations indicate a change in winter rainfall, with the change points being late in the last century or early in the present century.” Srikanthan, R. & Stewart, B. J., 1991, Aust. Meteorol. Mag. 39, 11–20. [full text]

Recent climatic change in Australia: Implications for a CO2-warmed earth – Pittock (1983) “A significant change in mean precipitation occurred over much of Australia between 1913–45 and 1946–78. This is described on a seasonal basis and related to possible changes in the atmospheric circulation. It now appears that during this time mean surface temperatures in the mid southern latitude zone increased by up to 1 °C. This temperature change could be at least partly due to an increase in atmospheric CO2 concentrations from about 260 ppmv in the early nineteenth century. In any case the observed temperature increase is similar to the predicted future effects of a 50% increase in atmospheric CO2 concentrations. Thus the climatic change which occurred earlier this century is at least a good analogy for the effects of a CO2-induced global warming which is expected to occur over a similar time interval in the future. This allows the construction of more detailed and quantitative climate scenarios. The most noteworthy conclusion is that marked changes in the seasonally of precipitation should be anticipated, with seasonal changes in some areas being of the order of 50% or more for a doubling of CO2 content. The results are in general consistent with earlier more qualitative scenarios for Australia.” A. B. Pittock, Climatic Change, Volume 5, Number 4, 321-340, DOI: 10.1007/BF02423529.

On the Detection of Climate Change – Doran & McGilchrist (1983) “In recent times, a body of opinion has developed supporting a conclusion that an abrupt change in the general climatic mechanisms occurred in some regions of Australia during the 1940’s. Such changes if significant, would have extensive repercussions in hydrologic design and analysis. Most practical procedures rely on an assumption of stationarity and in general the existence of significant non-stationarity will increase markedly the uncertainty in design. Because of the lack of conclusive physical evidence in the short term, the detection of climatic change must be carried out using statistical methods. A method which avoids the problems of assuming or deciding on an underlying probability distribution is the distribution-free CUSUM technique. This method has been used in an analysis of long-term annual rainfalls for the continent of Australia. The case for climate change will be considered on the basis of the results from this analysis. Comparisons of these results and those of previous analyses will be presented.” Doran, DG and McGilchrist, CA. On the Detection of Climate Change [online]. In: Hydrology and Water Resources Symposium (15th : 1983 : Hobart, Tas.). Hydrology and Water Resources Symposium 1983: Preprints of Papers. Barton, ACT: Institution of Engineers, Australia, 1983: 113-117. National conference publication (Institution of Engineers, Australia) ; no. 83/13.

Geographic variation in seasonal rainfall in Australia – an analysis of the 80-year period 1895-1974 – Russell (1981) As described by Srikanthan & Stewart (1991): “In examining the variation in summer and winter rainfall from 200 widely spread stations in Australia over the 80-year period (1895-1974), Russell (1981) found significant increases in summer rainfall at 42 stations, mostly in southeastern Australia. Only two stations showed significant decreases. In contrast, only seven stations showed significant increases in winter rainfall and five showed significant decreases.” Russell, J. S., 1981, Journal of the Australian Institute of Agricultural Science, v. 47(2) p. 59-66.

Changes in seasonal and annual rainfall in New South Wales – Cornish (1977) As described by Srikanthan & Stewart (1991): “From the analysis of annual and monthly rainfall totals for 99 stations throughout New South Wales, Cornish (1977) observed an increase in annual and summer rainfall in central New South Wales.” Cornish, P. M., 1977, Search, 8, 38–40.

Climate Change and the Pattern of Variation in Australian rainfall – Pittock (1975) As described by Srikanthan & Stewart (1991): “Pittock (1975, 1983) analysed 66 years (1913 to 1978) of Australian rainfall data and found an abrupt increase in rainfall circa 1945-46 over most of the continent. He attributes this to a change in climate.” Pittock, A. B., 1975, Search, 6, 498–503.

Climate change in Australia since 1880 – Deacon (1953) As described by Srikanthan & Stewart (1991): “This is in agreement with Deacon (1953), who showed that the summer rainfall over much of the southern part of Australia for the period 1911-1950 was considerably greater than that in the previous 30 years.” Deacon, E. L., 1953, Australian Journal of Physics, 6, 209-18.

Secular change in the rainfall regime of SE Australia – Kraus (1953) As described by Srikanthan & Stewart (1991): “Analysis of long-term rainfall series from Victoria and New South Wales (Kraus 1953) showed a decrease of summer rainfall to a minimum about the turn of the century and fifty years of gradual increase since then.” Kraus, E. B., 1954, Q. Jl R. met. Soc., 80, 591-601. (The publication year is either 1953 or 1954 – Srikanthan & Stewart give different years in their text and in their reference list.)

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New research from last week 1/2011

Posted by Ari Jokimäki on January 10, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Forest fires expected to increase in Finland

Climate change impacts on forest fire potential in boreal conditions in Finland – Kilpeläinen et al. (2011) “The aim of this work was to study the forest fire potential and frequency of forest fires under the projected climate change in Finland (N 60°–N 70°). Forest fire index, generally utilized in Finland, was used as an indicator for forest fire potential due to climatological parameters. Climatic scenarios were based on the A2 emission scenario. According to the results, the forest fire potential will have increased by the end of this century; as a result of increased evaporative demand, which will increase more than the rise in precipitation and especially in southern Finland. The annual number of forest fire alarm days is expected to increase in southern Finland to 96–160 days by the end of this century, compared to the current 60–100 days. In the north, the corresponding increase was from 30 to 36 days. The expected increase in the annual frequency of forest fires over the whole country was about 20% by the end of this century compared to the present day. The greatest increase in the frequency of fires, per 1,000 km2, was in the southernmost part of the country, with six to nine fires expected annually per 1,000 km2 at the end of this century, meaning a 24–29% increase compared to the present day frequencies.” Antti Kilpeläinen, Seppo Kellomäki, Harri Strandman and Ari Venäläinen, Climatic Change, Volume 103, Numbers 3-4, 383-398, DOI: 10.1007/s10584-009-9788-7.

Adaptation has already saved lives in England

Causes for the recent changes in cold- and heat-related mortality in England and Wales – Christidis et al. (2011) “Cold related mortality among people aged over 50 in England and Wales has decreased at a rate of 85 deaths per million population per year over the period 1976–2005. This trend is two orders of magnitude higher than the increase in heat-related mortality observed after 1976. Long term changes in temperature-related mortality may be linked to human activity, natural climatic forcings, or to adaptation of the population to a wider range of temperatures. Here we employ optimal detection, a formal statistical methodology, to carry out an end to end attribution analysis. We find that adaptation is a major influence on changing mortality rates. We also find that adaptation has prevented a significant increase in heat-related mortality and considerably enhanced a significant decrease in cold-related mortality. Our analysis suggests that in the absence of adaptation, the human influence on climate would have been the main contributor to increases in heat-related mortality and decreases in cold-related mortality.” Nikolaos Christidis, Gavin C. Donaldson and Peter A. Stott, Climatic Change, Volume 102, Numbers 3-4, 539-553, DOI: 10.1007/s10584-009-9774-0. [conference article]

Iron fertilization not effective in mitigating ocean acidification

Can ocean iron fertilization mitigate ocean acidification? – Cao & Caldeira (2011) “Ocean iron fertilization has been proposed as a method to mitigate anthropogenic climate change, and there is continued commercial interest in using iron fertilization to generate carbon credits. It has been further speculated that ocean iron fertilization could help mitigate ocean acidification. Here, using a global ocean carbon cycle model, we performed idealized ocean iron fertilization simulations to place an upper bound on the effect of iron fertilization on atmospheric CO2 and ocean acidification. Under the IPCC A2 CO2 emission scenario, at year 2100 the model simulates an atmospheric CO2 concentration of 965 ppm with the mean surface ocean pH 0.44 units less than its pre-industrial value of 8.18. A globally sustained ocean iron fertilization could not diminish CO2 concentrations below 833 ppm or reduce the mean surface ocean pH change to less than 0.38 units. This maximum of 0.06 unit mitigation in surface pH change by the end of this century is achieved at the cost of storing more anthropogenic CO2 in the ocean interior, furthering acidifying the deep-ocean. If the amount of net carbon storage in the deep ocean by iron fertilization produces an equivalent amount of emission credits, ocean iron fertilization further acidifies the deep ocean without conferring any chemical benefit to the surface ocean.” Long Cao and Ken Caldeira, Climatic Change, Volume 99, Numbers 1-2, 303-311, DOI: 10.1007/s10584-010-9799-4. [full text]

European temperature records of the past five centuries

European temperature records of the past five centuries based on documentary/instrumental information compared to climate simulations – Zorita et al. (2011) “Two European temperature reconstructions for the past half-millennium, January-to-April air temperature for Stockholm (Sweden) and seasonal temperature for a Central European region, both derived from the analysis of documentary sources and long instrumental records, are compared with the output of climate simulations with the model ECHO-G. The analysis is complemented by comparisons with the long (early)-instrumental record of Central England Temperature (CET). Both approaches to study past climates (simulations and reconstructions) are burdened with uncertainties. The main objective of this comparative analysis is to identify robust features and weaknesses in each method which may help to improve models and reconstruction methods. The results indicate a general agreement between simulations obtained with temporally changing external forcings and the reconstructed Stockholm and CET records for the multi-centennial temperature trend over the recent centuries, which is not reproduced in a control simulation. This trend is likely due to the long-term change in external forcing. Additionally, the Stockholm reconstruction and the CET record also show a clear multi-decadal warm episode peaking around AD 1730, which is absent in the simulations. Neither the reconstruction uncertainties nor the model internal climate variability can easily explain this difference. Regarding the interannual variability, the Stockholm series displays, in some periods, higher amplitudes than the simulations but these differences are within the statistical uncertainty and further decrease if output from a regional model driven by the global model is used. The long-term trend of the CET series agrees less well with the simulations. The reconstructed temperature displays, for all seasons, a smaller difference between the present climate and past centuries than is seen in the simulations. Possible reasons for these differences may be related to a limitation of the traditional ‘indexing’ technique for converting documentary evidence to temperature values to capture long-term climate changes, because the documents often reflect temperatures relative to the contemporary authors’ own perception of what constituted ‘normal’ conditions. By contrast, the amplitude of the simulated and reconstructed inter-annual variability agrees rather well.” Eduardo Zorita, Anders Moberg, Lotta Leijonhufvud, Rob Wilson, Rudolf Brázdil, Petr Dobrovolný, Jürg Luterbacher, Reinhard Böhm, Christian Pfister and Dirk Riemann, et al., Climatic Change, Volume 101, Numbers 1-2, 143-168, DOI: 10.1007/s10584-010-9824-7. [conference presentation]

Link between Tibetan Plateau snow cover and North American winter temperature

Contribution of the autumn Tibetan Plateau snow cover to seasonal prediction of North American winter temperature – Lin & Wu (2011) “Predicting surface air temperature (Ts) is a major task of North American (NA) winter seasonal prediction. It has been recognized that variations of the NA winter Ts can be associated with El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). This study presents observed evidence that variability in snow cover over the Tibetan Plateau (TP) and its adjacent areas in prior autumn (September–November) is significantly correlated with the first principal component (PC1) of the NA winter Ts which features a meridional seesaw pattern over the NA continent. The autumn TP snow cover anomaly can persist into the following winter through a positive feedback between snow cover and the atmosphere. A positive TP snow cover anomaly may induce a negative sea level pressure and geopotential height anomaly over the eastern North Pacific, a positive geopotential height anomaly over Canada, and a negative anomaly over southeast US, a structure very similar to the positive phase of the Pacific-North American (PNA) pattern. This usually favors the occurrence of a warm-North-cold-South winter over the NA continent. When a negative snow cover anomaly occurs, the situation tends to be opposite. Since the autumn TP snow cover shows a weak correlation with ENSO, it provides a new predictability source for NA winter Ts. Based on the above results, an empirical model is constructed to predict PC1 by a combination of autumn TP snow cover and other sea surface temperature anomalies related to ENSO and the NAO. Hindcasts and real forecasts are performed for the 1972–2003 and 2004–2009 periods, respectively. Both show a promising prediction skill. As far as PC1 is concerned, the empirical model hindcast performs better than the ensemble mean of four dynamical models from the Canadian Meteorological Center. Particularly, the real forecast of the empirical model exhibits a better performance in predicting the extreme phases of PC1, i.e., the extremely warm winter over Canada in 2009/2010, should the model include the autumn TP snow cover impacts. Since all these predictors can be readily monitored in real time, this empirical model provides a real time forecast tool for NA winter climate.” Hai Lin and Zhiwei Wu, Journal of Climate, 2011.

Linear trend not best way to describe long term SST trends

Testing for deterministic trends in global sea surface temperature – Barbosa (2011) “Long-term variability in global sea surface temperature (SST) is often quantified by the slope from a linear regression fit. Attention is then focused on assessing the statistical significance of the derived slope parameter, but the adequacy of the linear model itself, and the inherent assumption of a deterministic linear trend, is seldom tested. Here, a parametric statistical test is applied to test the hypothesis of a linear deterministic trend in global sea surface temperature. The results show that a linear slope is not adequate for describing the long-term variability of sea surface temperature over most of the Earth’s surface. This doesn’t mean that sea surface temperature is not increasing, rather that the increase shouldn’t be characterized by the slope from a linear fit. Therefore, describing the long-term variability of sea surface temperature by implicitly assuming a deterministic linear trend can give misleading results, particularly in terms of uncertainty, since the actual increase could be considerably larger than the one predicted by a deterministic linear model.” Susana M. Barbosa, Journal of Climate, 2011.

Lake in Germany shows human impact 1000s of years ago

Climate change and human impact at Sacrower See (NE Germany) during the past 13,000 years: a geochemical record – Enters et al. (2011) “Lacustrine sediments in north-eastern Germany have rarely been used as archives to address the effects of climate change and human impact on both lake ecosystem and landscape evolution for this region. Sacrower See, a hardwater lake located in Brandenburg, provides a unique sediment record covering the past 13,000 years which was used to reconstruct climatic and anthropogenic forcing on lacustrine sedimentation. Time control is provided by 12 AMS 14C dates of terrestrial plant remains, the Laacher See Tephra, and the onset of varve formation in AD 1870 (80 cal. BP). Geochemical (including XRF logging of major elements, CNS analyses as well as δ13Corg and δ15N measurements) and pollen analyses allowed detecting detailed environmental changes in the sediment record. During the Younger Dryas cold phase increased soil erosion and hypolimnetic oxygen depletion enhanced the nutrient supply to the lake water causing eutrophic conditions. The beginning of the Holocene is characterized by large changes in C/N ratios, total sulphur, δ13C of bulk organic matter as well as in K, Si, and Ti, reflecting the response of the lake’s catchment to climatic warming. Reforestation reduced the influx of detrital particles and terrestrial organic matter. The first, rather weak evidence of human impact is documented only in the pollen record at 5,500 cal. BP. However, until 3,200 cal. BP sedimentological and geochemical parameters indicate relatively stable environmental conditions. During periods of intense human impact at around 3,200, 2,800, and 900 cal. BP peaks in Ti and K represent phases of increased soil erosion due to forest clearing during the Bronze Age, Iron Age, and Medieval Times, respectively. In general, greater variation is observed in most variables during these perturbations, indicating less stable environmental conditions. The steady rise of biogenic silica accumulation rates during the Holocene reflects an increasing productivity of Sacrower See until diatoms were outcompeted by other algae during the last centuries. The applied multi-proxy approach fosters the interpretation of the sediment record to reveal a consistent picture of environmental change including environmental factors controlling lake ontogeny and the effects of human impact.” D. Enters, E. Kirilova, A. F. Lotter, A. Lücke, J. Parplies, S. Jahns, G. Kuhn and B. Zolitschka, Journal of Paleolimnology, Volume 43, Number 4, 719-737, DOI: 10.1007/s10933-009-9362-3.

Climate effect of volcanoes depend on time of the year

Climate effects of high-latitude volcanic eruptions: Role of the time of year – Kravitz & Robock (2011) “We test how the time of year of a large Arctic volcanic eruption determines the climate impacts by conducting simulations with a general circulation model of Earth’s climate. For eruptions injecting less than about 3 Tg of SO2 into the lower stratosphere, we expect no detectable climatic effect, no matter what the season of the eruption. For an injection of 5 Tg of SO2 into the lower stratosphere, an eruption in the summer would cause detectable climate effects, whereas an eruption at other times of the year would cause negligible effects. This is mainly due to the seasonal variation in insolation patterns and sulfate aerosol deposition rates. In all cases, the sulfate aerosols that form get removed from the atmosphere within a year after the eruption by large-scale deposition. Our simulations of a June eruption have many similar features to previous simulations of the eruption of Katmai in 1912, including some amount of cooling over Northern Hemisphere continents in the summer of the eruption, which is an expected climate response to large eruptions. Previous Katmai simulations show a stronger climate response, which we attribute to differences in choices of climate model configurations, including their specification of sea surface temperatures rather than the use of a dynamic ocean model as in the current simulations.” Kravitz, B., and A. Robock (2011), J. Geophys. Res., 116, D01105, doi:10.1029/2010JD014448. [full text]

Atmosphere’s self-cleaning capacity is rather stable

NOAA news release

SPESTMW increases under global warming

Increase of South Pacific eastern subtropical mode water under global warming – Luo et al. (2011) “The response of South Pacific Eastern Subtropical Mode Water (SPESTMW) to global warming is investigated by comparing solutions from a set of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled models between a present-day climate and a future, warmer climate. Under the warmer climate scenario, the SPESTMW extends southwestward and is significantly increased in volume. This is because all the local surface forcing mechanisms (i.e., wind stress, heat and freshwater fluxes) in the eastern subtropical South Pacific tends to de-stratify the upper ocean and thus deepen the mixed layer. Further, a suite of process-oriented experiments with an ocean general circulation model suggest that it is the intensified southeast trade winds under the warmer climate that promotes more heat flux from the ocean into the atmosphere that then results in a deepening of the mixed layer in the eastern subtropics of the South Pacific.” Luo, Y., Q. Liu, and L. M. Rothstein (2011), Geophys. Res. Lett., 38, L01601, doi:10.1029/2010GL045878.

NAO relation to summer climate in Europe

A summer climate regime over Europe modulated by the North Atlantic Oscillation – Wang et al. (2011) “Recent summer heat waves in Europe were found to be preceded by precipitation deficits in winter. Numerical studies suggest that these phenomena are dynamically linked by land-atmosphere interactions. However, there exists as yet no complete observational evidence that connects summer climate variability to winter precipitation and the relevant circulation patterns. In this paper, we investigate the functional responses of summer mean and maximum temperature (June–August, Tmean and Tmax) as well as soil moisture proxied by the self-calibrating Palmer drought severity index (scPDSI) to preceding winter precipitation (January–March, PJFM) for the period 1901–2005. All the analyzed summer fields show distinctive responses to PJFM over the Mediterranean. We estimate that 10 ~ 15% of the interannual variability of Tmax and Tmean over the Mediterranean is statistically forced by PJFM. For the scPDSI this amounts to 10 ~ 25%. Further analysis shows that these responses are highly correlated to the North Atlantic Oscillation (NAO) regime over the Mediterranean. We suggest that NAO modulates European summer temperature by controlling winter precipitation that initializes the moisture states that subsequently interact with temperature. This picture of relations between European summer climate and NAO as well as winter precipitation suggests potential for improved seasonal prediction of summer climate for particular extreme events.” Wang, G., Dolman, A. J., and Alessandri, A.: A summer climate regime over Europe modulated by the North Atlantic Oscillation, Hydrol. Earth Syst. Sci., 15, 57-64, doi:10.5194/hess-15-57-2011, 2011. [full text]

Studying Greenland ice sheet sliding with radar

Radar images of the bed of the Greenland Ice Sheet – Jezek et al. (2011) “In this paper, we apply radar tomography methods to very-high-frequency, airborne synthetic-aperture radar data to measure the ice thickness field and to construct three-dimensional basal image maps of a 5 × 20 km study area located along the southern flank of the Jakobshavn Glacier, Greenland. Unlike ice radar measurements typically made at nadir, our approach uses radar-echo phase and amplitude measured across an antenna array to determine the propagation angle and signal strength of pixel elements distributed on each side of the aircraft flight path. That information, combined with knowledge of aircraft position and the assumed dielectric properties of the glacier, can be used to measure ice thickness and radar reflectivity across a 3-km wide swath. Combining ice thickness and surface topography data, we estimate basal topography and basal drag. We conclude that the glacier is sliding over the bed. We use the three-dimensional image maps of the bed to inspect the modern subglacial geomorphology and find for the first time beneath the Greenland Ice Sheet assemblages of long ridge-groove landforms that are oriented in the direction of the ice flow. Spatial dimensions (10 to 30 m depths, 150 to 500 m spacing and lengths of 10 km or more) and correlation with the current ice flow direction suggest that these are glacial erosional features similar to mega-grooves observed on deglaciated terrain.” Jezek, K., X. Wu, P. Gogineni, E. Rodríguez, A. Freeman, F. Rodriguez-Morales, and C. D. Clark (2011), Geophys. Res. Lett., 38, L01501, doi:10.1029/2010GL045519.

Estimating global solar radiation

Statistical downscaling with Bayesian inference: Estimating global solar radiation from reanalysis and limited observed data – Iizumi et al. (2011) “Daily global solar radiation (SR) is one of essential weather inputs for crop, hydrological, and other simulation models to calculate biomass production and potential evapotranspiration. The availability of long-term observed SR data is, however, limited, especially in developing countries. This hinders climate applications in various sectors in these countries. To overcome this difficulty, we here propose a method to infer the reasonable daily SR condition for past decades from global reanalysis and limited observed SR data. The method consists of the regression-based statistical downscaling method and two empirical models for estimating the SR condition (i.e. the S-model and the DTR/RH-model). These empirical models were independent in terms of the variables explaining the SR condition. The regression models were trained on the basis of the SR conditions estimated by the S-model and the DTR/RH-model instead of the observed SR data. The Markov Chain Monte Carlo (MCMC) technique was applied to determine the parameter values of these models that guide the models to provide SR conditions that are close in value to each other at both the site and domain-mean scales. After that, we computed the SR condition over the 30 years from 1978 through 2007 at 17 sites in the Vietnam Mekong Delta area using the determined parameter values. The inferred SR condition was close in value to the corresponding observations available from the literature. This suggests that the proposed method yielded a reasonable inference of the SR condition at the sites despite the limited availability of observed SR data. The provided estimates of the daily SR condition over the past 30 years are useful for climate applications in agricultural, hydrological, and other sectors in this area.” Toshichika Iizumi, Motoki Nishimori, Masayuki Yokozawa, Akihiko Kotera, Nguyen Duy Khang, International Journal of Climatology, DOI: 10.1002/joc.2281.

Posted in Climate science | 5 Comments »

Papers on weekly cycle in climate

Posted by Ari Jokimäki on January 5, 2011

This is a list of papers showing observations of weekly cycle in climate related variables. Weekly cycle in climate parameters is suggestive of anthropogenic control. Papers on so called “weekend effect” are also included. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (February 5, 2012): Asmi (2012) and Pollack et al. (2012) added.
UPDATE (November 5, 2011): Rosenfeld & Bell (2011) and Tuttle & Carbone (2011) added.

Airborne and ground-based observations of a weekend effect in ozone, precursors, and oxidation products in the California South Coast Air Basin – Pollack et al. (2012) “Airborne and ground-based measurements during the CalNex (California Research at the Nexus of Air Quality and Climate Change) field study in May/June 2010 show a weekend effect in ozone in the South Coast Air Basin (SoCAB) consistent with previous observations. The well-known and much-studied weekend ozone effect has been attributed to weekend reductions in nitrogen oxide (NOx = NO + NO2) emissions, which affect ozone levels via two processes: (1) reduced ozone loss by titration and (2) enhanced photochemical production of ozone due to an increased ratio of non-methane volatile organic compounds (VOCs) to NOx. In accord with previous assessments, the 2010 airborne and ground-based data show an average decrease in NOx of 46 ± 11% and 34 ± 4%, respectively, and an average increase in VOC/NOx ratio of 48 ± 8% and 43 ± 22%, respectively, on weekends. This work extends current understanding of the weekend ozone effect in the SoCAB by identifying its major causes and quantifying their relative importance from the available CalNex data. Increased weekend production of a VOC-NOx oxidation product, peroxyacetyl nitrate, compared to a radical termination product, nitric acid, indicates a significant contribution from increased photochemical production on weekends. Weekday-to-weekend differences in the products of NOx oxidation show 45 ± 13% and 42 ± 12% more extensive photochemical processing and, when compared with odd oxygen (Ox = O3 + NO2), 51 ± 14% and 22 ± 17% greater ozone production efficiency on weekends in the airborne and ground-based data, respectively, indicating that both contribute to higher weekend ozone levels in the SoCAB.” Pollack, I. B., et al. (2012), Airborne and ground-based observations of a weekend effect in ozone, precursors, and oxidation products in the California South Coast Air Basin, J. Geophys. Res., 117, D00V05, doi:10.1029/2011JD016772.

Weakness of the weekend effect in aerosol number concentrations – Asmi (2012) “Weekday related anthropogenic aerosol emissions have been suggested to affect regional climate via indirect aerosol effects. I studied the variability of potential cloud condensation nuclei using measurements of number size distributions of Cloud Condensation Nuclei (CCN) -sized aerosol particles and CCNs measured at several European regional background stations, located at a wide variety of environments. With notably rare exceptions, there were no statistically significant difference between concentrations on different weekdays. I further analysed the concentration timeseries of four long-period datasets in Germany and Finland with wavelet analysis. Outside of urban areas, very little weekday-connected variability was found. The lack of 7-day variability outside of cities is in contrast of earlier studies in this field, which used mostly particle mass as the representative measure of aerosol concentration. A time-scale and variability analysis showed that PM10 and PM2.5 are more sensitive for the weekly variation than CCN-sized particles. Using mass-based variations as a proxy for short-term variations of CCN particle numbers can thus overestimate the weekend effect for these particles. The results of this study do not support aerosol indirect effects from 50 to 500 nm diameter particles as a major contributor on potential weekday connected variations in European meteorology.” Ari Asmi, Atmospheric Environment,

Inferences of weekly cycles in summertime rainfall – Tuttle & Carbone (2011) “In several continental regions a weekly cycle of air pollution aerosols has been observed. It is usually characterized by concentration minima on weekends (Saturday and Sunday) and maxima on weekdays (Tuesday–Friday). Several studies have associated varying aerosol concentrations with precipitation production and attempted to determine whether or not there is a corresponding weekly cycle of precipitation. Results to date have been mixed. Here we examine a 12 year national composited radar data set for evidence of weekly precipitation cycles during the warm season (June–August). Various statistical quantities are calculated and subjected to “bootstrap” testing in order to assess significance. In many parts of the United States, warm season precipitation is relatively infrequent, with a few extreme events contributing to a large percentage of the total 12 year rainfall. For this reason, the statistics are often difficult to interpret. The general area east of the Mississippi River and north of 37°N contains regions where 25%–50% daily rainfall increases are inferred for weekdays (Tuesday–Friday) relative to weekends. The statistics suggest that western Pennsylvania is the largest and most likely contiguous region to have a weekly cycle. Parts of northern Florida and southeastern coastal areas infer a reverse-phase cycle, with less rainfall during the week than on weekends. Spot checks of surface rain gauge data confirm the phase of these radar-observed anomalies in both Pennsylvania and Florida. While there are indications of a weekly cycle in other locations of the United States, the degree of confidence is considerably lower. There is a strong statistical inference of weekday rainfall maxima over a net 8% of the area examined, which is approximately twice the area of cities. Future examination of lofted aerosol content, related condensation/ice nuclei spectra, and knowledge of the convective dynamical regime are needed in order to assess how anthropogenic aerosols may affect rainfall at urban and regional scales. If radar is the primary method of observation, it is also necessary to examine the effects of variable aerosol content on the parametric relationship between rainfall rate and radar reflectivity factor. Polarimetric radar observations could also serve to verify microphysical-dynamical hypotheses regarding precipitation production.” Tuttle, J. D., and R. E. Carbone (2011), J. Geophys. Res., 116, D20213, doi:10.1029/2011JD015819.

Why do tornados and hailstorms rest on weekends? – Rosenfeld & Bell (2011) “This study shows for the first time statistical evidence that when anthropogenic aerosols over the eastern United States during summertime are at their weekly mid-week peak, tornado and hailstorm activity there is also near its weekly maximum. The weekly cycle in summertime storm activity for 1995–2009 was found to be statistically significant and unlikely to be due to natural variability. It correlates well with previously observed weekly cycles of other measures of storm activity. The pattern of variability supports the hypothesis that air pollution aerosols invigorate deep convective clouds in a moist, unstable atmosphere, to the extent of inducing production of large hailstones and tornados. This is caused by the effect of aerosols on cloud drop nucleation, making cloud drops smaller and hydrometeors larger. According to simulations, the larger ice hydrometeors contribute to more hail. The reduced evaporation from the larger hydrometeors produces weaker cold pools. Simulations have shown that too cold and fast-expanding pools inhibit the formation of tornados. The statistical observations suggest that this might be the mechanism by which the weekly modulation in pollution aerosols is causing the weekly cycle in severe convective storms during summer over the eastern United States. Although we focus here on the role of aerosols, they are not a primary atmospheric driver of tornados and hailstorms but rather modulate them in certain conditions.” Rosenfeld, D., and T. L. Bell (2011), J. Geophys. Res., 116, D20211, doi:10.1029/2011JD01.

An Empirical Study of Geographic and Seasonal Variations in Diurnal Temperature Range – Jackson & Forster (2010) “The diurnal temperature range (DTR) of surface air over land varies geographically and seasonally. The authors have investigated these variations using generalized additive models (GAMs), a nonlinear regression methodology. With DTR as the response variable, meteorological and land surface parameters were treated as explanatory variables. Regression curves related the deviation of DTR from its mean value to values of the meteorological and land surface variables. Cloud cover, soil moisture, distance inland, solar radiation, and elevation were combined as explanatory variables in an ensemble of 84 GAM models that used data grouped into seven vegetation types and 12 months. The ensemble explained 80% of the geographical and seasonal variation in DTR. Vegetation type and cloud cover exhibited the strongest relationships with DTR. Shortwave radiation, distance inland, and elevation were positively correlated with DTR, whereas cloud cover and soil moisture were negatively correlated. A separate analysis of the surface energy budget showed that changes in net longwave radiation represented the effects of solar and hydrological variation on DTR. It is found that vegetation and its associated climate is important for DTR variation in addition to the climatic influence of cloud cover, soil moisture, and solar radiation. It is also found that surface net longwave radiation is a powerful diagnostic of DTR variation, explaining over 95% of the seasonal variation of DTR in tropical regions.” Jackson, Lawrence S., Piers M. Forster, 2010, J. Climate, 23, 3205–3221, doi: 10.1175/2010JCLI3215.1.

Weekend effect: Anthropogenic or natural? – Kim et al. (2010) “Human activities have been suggested to result in weekly changes of meteorological variables, called the “weekend effect.” Recent debates on its statistical significance, however, reveal that there still remain huge uncertainties as to the anthropogenic origin of the weekend effect. We show that atmospheric Rossby waves induce the “natural” weekend effect, which is much stronger than the “anthropogenic” weekend effect. The “natural” weekend effect does not completely disappear even with averaging over 61 years of data; as a result, true “anthropogenic” weekend effect is obscured by the natural component. We attempted to remove the “natural” component in the diurnal temperature range and the resulting pattern is an overall positive weekend effect over North America.” Kim, K.-Y., R. J. Park, K.-R. Kim, and H. Na (2010), Geophys. Res. Lett., 37, L09808, doi:10.1029/2010GL043233. [full text]

The Detection of Weekly Preferential Occurrences with an Application to Rainfall – Marani (2010) “The detection of weekly preferential occurrences in atmospheric and hydrologic processes has recently attracted much attention as a way to identify the signature of anthropogenic climatic changes. The interpretation of previous analyses, however, is not unequivocal, in part as a result of a lack of widely accepted statistical criteria. Here, a general and exact method to detect the presence of weekly preferential occurrences is developed and applied to long rainfall observations in Marghera, Italy; Philadelphia, Pennsylvania; and Portland, Maine. The method makes use of the fact that, under the null hypothesis of stationarity, the process of event occurrence in the different days of the week is equivalent to the random distribution of a number of balls (the wet days) in a set of boxes (the days of the week). The departure from a homogeneous distribution is then characterized through the probability of the maximum number of balls in a box, which can be computed exactly with no ad hoc assumptions. The new method shows that (i) preferential rainfall weekly occurrences emerge in all cases in the most recent period analyzed (1990–2006), while they are absent—or are too weak to be detected—in previous years (before 1989); and (ii) the balls-in-boxes approach appears to be more sensitive than Pearson’s test when deviations from homogeneity are associated with just one day of the week, a common occurrence in connection with day-of-the-week effects. The results presented help to reconcile previous contrasting studies and to contribute compelling evidence that anthropogenic changes in the local climate have occurred over the past century in urban and industrial areas.” Marani, Marco, 2010, J. Climate, 23, 2379–2387, doi: 10.1175/2009JCLI3313.1.

Day-of-the-week variations of urban temperature and their long-term trends in Japan – Fujibe (2010) “Temperature differences among days of the week and their long-term trends were evaluated using 29 years of hourly data from the Automated Meteorological Data Acquisition System network of Japan. Stations were categorized with respect to the population density around each site, and an urban temperature anomaly (δT*) was defined as a departure from the spatial average of nearby rural stations. On Saturdays and holidays (Sundays and national holidays), δT* was lower than on weekdays by 0.2–0.25°C at Tokyo, by 0.1–0.2°C at Osaka, and by about 0.02°C at stations where the population density was 300 to 1,000 km–2. Moreover, δT* showed a relative decreasing trend over the long term on Mondays and an increasing trend on Fridays, at a rate of about 0.05–0.1°C decade–1 at Tokyo and about 0.02°C decade–1 at stations where the population density was 100 to 1,000 km–2, but no significant difference in δT* trends was observed between weekdays and weekend days.” Fumiaki Fujibe, Theoretical and Applied Climatology, Volume 102, Numbers 3-4, 393-401, DOI: 10.1007/s00704-010-0266-y.

Long-term changes in summer weekend effect over northeastern China and the connection with regional warming – Ho et al. (2009) “The 7-day cycle of human activities may lead to the “weekend effect” in climate variables and air pollutants. The weekend effect is defined as the average value (e.g., the diurnal temperature range) for Saturday through Monday minus the average value for Wednesday through Friday. A composite of the ground observations over northeastern China presents that, during 26-year (1980–2005) summers, the weekend effect in the diurnal temperature range increased by 1.2°C. Conversely, the weekend effects in the relative humidity, cloud amount, and light rain (≤5 mm day−1) events decreased. These changes are due to a shifted phase of the weekly cycle of the meteorological variables. The long-term change in weekend effects have a high correlation coefficient (∣r∣ ≈ 0.8) with the decrease in relative humidity over the region, which is likely induced by regional warming. The results suggest that regional warming is a possible factor in a transition of dominant aerosol effects in the weekend effect.” Ho, C.-H., Y.-S. Choi, and S.-K. Hur (2009), Geophys. Res. Lett., 36, L15706, doi:10.1029/2009GL039509.

Weekly periodicities of Aerosol Optical Thickness over Central Europe – evidence of an anthropogenic direct aerosol effect – Bäumer et al. (2008) “Statistical analyses of data from ground-based sun photometer stations in Central Europe are presented. All stations are part of the Aerosol Robotic Network (AERONET), and only data of the highest data quality level 2.0 has been applied. The averages by weekday of Aerosol Optical Thickness (AOT) at a wavelength of 440 nm of 12 of the 14 stations in the investigation area show a weekly periodicity with lowest values on Sunday and Monday, but greatest values from Wednesday until Saturday, that is significant at least on a 90% level. The stations in Germany and in Greater Paris show weekly cycles with ranges of about 20% on average. In Northern Italy and Switzerland this range is about 10% on average. By applying several checks, we exclude that the weekly cycles were caused by a maintenance effect or by different retrieval conditions as a consequence of a weekly cycle in cloud cover. The corresponding weekly cycle of anthropogenic gaseous and particulate emissions leads us to the conclusion of the anthropogenic origin of the weekly AOT cycle. Since these AOT patterns are derived from the reduction of the direct sun radiation by the columnar atmospheric aerosol, this result represents strong evidence for an anthropogenic direct aerosol effect on shortwave radiation. Furthermore, this study makes a first contribution to the understanding and explanation of recently observed weekly periodicities in meteorological variables as temperature in Germany.” Bäumer, D., Rinke, R., and Vogel, B., Atmos. Chem. Phys., 8, 83-90, doi:10.5194/acp-8-83-2008, 2008. [full text]

Winter “weekend effect” in southern Europe and its connections with periodicities in atmospheric dynamics – Sanchez-Lorenzo et al. (2008) “Winter weekly cycles of different climatic variables have been detected over Spain during the 1961–2004 period. The 13 analyzed series come from stations placed on different climatological and geographical areas with different level of urban influence. Therefore, the weekly cycles can hardly be related with local effects. Contrarily, we suggest that the weekly cycles may be related with changes in the atmospheric circulation over Western Europe, which may be due to some indirect effect of anthropogenic aerosols. Particularly interesting is the observed increase in Sea Level Pressure over Southern Europe during the weekends and consequently a decrease of anticyclonic conditions during the central weekdays.” Sanchez-Lorenzo, A., J. Calbó, J. Martin-Vide, A. Garcia-Manuel, G. García-Soriano, and C. Beck (2008), Geophys. Res. Lett., 35, L15711, doi:10.1029/2008GL034160.

Analysis of the weekly cycle of aerosol optical depth using AERONET and MODIS data – Xia et al. (2008) “Multi-year Aerosol Robotic Network (AERONET) and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth (AOD) data are used to study AOD weekly variations at the global scale. A clear weekly cycle of AOD is observed in the United States (U.S.) and Central Europe. AOD during the weekday is larger than that during the weekend in 36 out of 43 AERONET sites in the U.S. The average U.S. weekend effect (the percent difference in AOD during the weekday and the weekend) is 3.8%. A weekly periodicity with lower AODs on Sunday and Monday and higher AODs from Wednesday until Saturday is revealed over Central Europe and the average weekend effect there is 4.0%. The weekly cycle in urban sites is greater than that in rural sites. AOD during the weekday is also significantly larger than that during the weekend in urban AERONET sites in South America and South Korea. However, a reversed AOD weekly cycle is observed in the Middle East and India. AODs on Thursday and Friday, the “weekend” for Middle East cultures, are relatively lower than AODs on other days. There is no clear weekly variation of AOD over eastern China. The striking feature in this region is the occurrence of much higher AOD on Sunday and this phenomenon is independent of season. The analysis of MODIS aerosol data is in good agreement with that of AERONET data.” Xia, X., T. F. Eck, B. N. Holben, G. Phillippe, and H. Chen (2008), J. Geophys. Res., 113, D14217, doi:10.1029/2007JD009604.

An unexpected pattern of distinct weekly periodicities in climatological variables in Germany – Bäumer & Vogel (2007) “Statistical analyses of data from 12 German meteorological stations meeting WMO standards in the period 1991–2005 are presented. These stations represent different local climate conditions in terms of both meteorology and pollution situation. For the average over data of all stations, we identified significant weekly periodicities in many variables such as temperature, daily temperature range, sunshine duration, cloud amount, precipitation, and precipitation frequency. Not only data of stations situated in congested urban areas, but also data of remote stations as e.g. on Mount Zugspitze 2960 m above sea level in the Alps showed significant in-phase weekly cycles. These weekly periodicities cannot be explained completely by local pollution effects or local heat emissions. We tend towards the hypothesis that the anthropogenic weekly emission cycle and the subsequent aerosol cycle interact with the atmospheric dynamics on a larger scale which leads to a forcing of a naturally existing 7-day period among the spectrum of atmospheric periods.” Bäumer, D., and B. Vogel (2007), Geophys. Res. Lett., 34, L03819, doi:10.1029/2006GL028559. [full text]

Weekly precipitation cycles? Lack of evidence from United States surface stations – Schultz et al. (2007) “Previous work has inferred a relationship between human activity and the occurrence and amount of precipitation through examining possible weekly cycles in precipitation. Daily precipitation records for 219 surface observing stations in the United States for the 42-year period 1951–1992 are investigated for weekly cycles in precipitation. Results indicate that neither the occurrence nor amount of precipitation significantly depends upon the day of the week.” Schultz, D. M., S. Mikkonen, A. Laaksonen, and M. B. Richman (2007), Geophys. Res. Lett., 34, L22815, doi:10.1029/2007GL031889. [full text]

Weekly cycle of aerosol-meteorology interaction over China – Gong et al. (2007) “Weekly cycles of the concentration of anthropogenic aerosols have been observed in many regions around the world. The phase and the magnitude of these cycles, however, vary greatly depending on region and season. In the present study the authors investigated important features of the weekly cycles of aerosol concentration and the covariations in meteorological conditions in major urban regions over east China, one of the most polluted areas in the world, in summertime during the period 2001–2005/2006. The PM10 (aerosol particulate matters of diameter < 10 μm) concentrations at 29 monitoring stations show significant weekly cycles with the largest values around midweek and smallest values in weekend. Accompanying the PM10 cycle, the meteorological variables also show notable and consistent weekly cycles. The wind speed in the lower troposphere is relatively small in the early part of the week and increases after about Wednesday. At the same time, the air temperature anomalies in low levels are positive and then become negative in the later part of the week. The authors hypothesize that the changes in the atmospheric circulation may be triggered by the accumulation of PM10 through diabatic heating of lower troposphere. During the early part of a week the anthropogenic aerosols are gradually accumulated in the lower troposphere. Around midweek, the accumulated aerosols could induce radiative heating, likely destabilizing the middle to lower troposphere and generating anomalously vertical air motion and thus resulting in stronger winds. The resulting circulation could promote ventilation to reduce aerosol concentrations in the boundary layer during the later part of the week. Corresponding to this cycle in anthropogenic aerosols the frequency of precipitation, particularly the light rain events, tends to be suppressed around midweek days through indirect aerosol effects. This is consistent with the observed anthropogenic weather cycles, i.e., more (less) solar radiation near surface, higher (lower) maximum temperature, larger (smaller) diurnal temperature range, and fewer (more) precipitation events in midweek days (weekend).” Gong, D.-Y., C.-H. Ho, D. Chen, Y. Qian, Y.-S. Choi, and J. Kim (2007), J. Geophys. Res., 112, D22202, doi:10.1029/2007JD008888. [full text, slide show]

Weekend effect in diurnal temperature range in China: Opposite signals between winter and summer – Gong et al. (2006) “Intense human activity can impact weather and climate in many ways. One possible important consequence is the weekly cycle (so-called weekend effect) in the diurnal temperature range (DTR). The weekend effect is defined as the average DTR for Saturday through Monday minus the average DTR for Wednesday through Friday. In the present study, the weekend effect in the DTR over east China combined with station observations of maximum and minimum temperatures, relative humidity, and total solar irradiance for the period 1955–2000 was analyzed. Results show that the weekend effect in the DTR has the opposite signal between winter (December, January, and February) and summer (June, July, and August). Wintertime DTR tends to have a positive weekend effect (i.e., larger DTR in weekend days compared to weekdays), in association with increased maximum temperature and total irradiance but decreased relative humidity. While summertime DTR displays a much stronger and significantly negative weekend effect (i.e., smaller DTR in weekend days), in association with decreased maximum temperature and total solar irradiance but increased relative humidity and a greater number of rainy days. This study indicates that the DTR difference between weekend and weekdays is predominantly related to weekly changes in the maximum temperature. The weekend effect in the DTR and maximum temperature is also found in the Reanalysis 2 data. The weekend effect in winter is supported by an analogous holiday (Spring Festival) effect. Since the late 1970s, the weekend effect has been enhanced in both winter and summer, concurrent with rapid development and enhanced human activity in China. The direct and indirect effects of human-related aerosols on radiation, cloud, precipitation, and so on, might play an important role in generating the opposite signal in the weekend effect for different seasons. During a dry winter, the reduction of aerosol concentrations may overwhelmingly impact on the DTR through a direct effect, i.e., by increasing total solar irradiance near the surface and raising the daytime temperature and maximum temperature and lowering relative humidity. By contrast, in summer the indirect effect of aerosols, i.e., reduction in precipitation efficiency caused by more numerous and smaller cloud droplets, would largely be responsible for the increased numbers of rainy days, the reduction of the total solar irradiance, and the lowering of the maximum temperature and DTR.” Gong, D.-Y., D. Guo, and C.-H. Ho (2006), J. Geophys. Res., 111, D18113, doi:10.1029/2006JD007068. [full text]

Comparison of 7 years of satellite-borne and ground-based tropospheric NO2 measurements around Milan, Italy – Ordóñez et al. (2006) “Tropospheric NO2 vertical column densities (VCDs) over the Lombardy region were retrieved from measurements of the Global Ozone Monitoring Experiment (GOME) spectrometer for the period 1996–2002 using a differential optical absorption method. This data set was compared with in situ measurements of NO2 at around 100 ground stations in the Lombardy region, northern Italy. The tropospheric NO2 VCDs are reasonably well correlated with the near-surface measurements under cloud-free conditions. However, the slope of the tropospheric VCDs versus ground measurements is higher in autumn-winter than in spring-summer. This effect is clearly reduced when the peroxyacetyl nitrate and nitric acid (HNO3) interferences of conventional NOx analyzers are taken into account. For a more quantitative comparison, the NO2 ground measurements were scaled to tropospheric VCDs using a seasonal NO2 vertical profile over northern Italy calculated by the Model of Ozone and Related Tracers 2 (MOZART-2). The tropospheric VCDs retrieved from satellite and those determined from ground measurements agree well, with a correlation coefficient R = 0.78 and a slope close to 1 for slightly polluted stations. GOME cannot reproduce the high NO2 amounts over the most polluted stations, mainly because of the large spatial variability in the distribution of pollution within the GOME footprint. The yearly and weekly cycles of the tropospheric NO2 VCDs are similar for both data sets, with significantly lower values in the summer months and on Sundays, respectively. Considering the pollution level and high aerosol concentrations of this region, the agreement is very good. Furthermore, uncertainties in the ground-based measurements, including the extrapolation to NO2 VCDs, might be as important as those of the NO2 satellite retrieval itself.” Ordóñez, C., A. Richter, M. Steinbacher, C. Zellweger, H. Nüß, J. P. Burrows, and A. S. H. Prévôt (2006), J. Geophys. Res., 111, D05310, doi:10.1029/2005JD006305. [full text]

Weekly periodicity of environmental variables in Phoenix, Arizona – Shutters & Balling (2006) “Though there is no known meteorological cause for weekly cycling of environmental variables, weekly cycles have been discovered at local to global scales, particularly in areas affected by human urbanization. To uncover such cycles in Phoenix, AZ, and to highlight possible mechanisms for their existence, data from several public domain sources were collected and analyzed for cycles in three categories of variables: meteorological, pollution, and human activity measured as vehicle traffic flows. Results indicated that many meteorological and pollution variables do exhibit weekly periodicity and that these cycles are likely due to the weekly pattern of human traffic flows. Atmospheric concentrations of O3 and NOX gases exhibit a high degree of negative correlation, supporting recent research that suggests anthropogenic NOX gases are effective scavengers of ozone in urban cores. Results further suggest that vehicle-generated NOX gases may be a significant generator of atmospheric nitrate particulates. Finally, both traffic flow and NOX gas concentrations display a strong correlation with wind speed in the urban core, though this study does not speculate on a mechanism for this relationship.” Shade T. Shutters and Robert C. Balling Jr., Atmospheric Environment, Volume 40, Issue 2, January 2006, Pages 304-310, doi:10.1016/j.atmosenv.2005.09.037.

Urban aerosols and their variations with clouds and rainfall: A case study for New York and Houston – Jin et al. (2005) “Diurnal, weekly, seasonal, and interannual variations of urban aerosols were analyzed with an emphasis on summer months using 4 years of the NASA Earth Observing System (EOS) Moderate Resolution Imaging Spectroradiometer (MODIS) observations, in situ Aerosol Robotic Network (AERONET) observations, and in situ U.S. Environmental Protection Agency (EPA) PM2.5 data for one midlatitude city (New York) and one subtropical city (Houston). Seasonality is evident in aerosol optical thickness measurements, with a minimum in January and a maximum in April to July. The diurnal variations of aerosols, however, are detectable but largely affected by local and regional weather conditions, such as surface and upper-level winds. On calm clear days, aerosols peak during the two rush hours in the morning and evening. Furthermore, the anthropogenic-induced weekly cycles of aerosols and clouds are analyzed, which by themselves are weak, as the anthropogenic signal is mixed with noise of natural weather variability. In addition, corresponding cloud properties observed from MODIS demonstrate an opposite phase to the seasonality of aerosols. Nevertheless, no clear relationship was observed between monthly mean aerosols and rainfall measurements from NASA’s Tropical Rainfall Measuring Mission (TRMM), implying that in the summer the aerosol impact may not be the primary reason for the change of urban rainfall amount.” Jin, M., J. M. Shepherd, and M. D. King (2005), J. Geophys. Res., 110, D10S20, doi:10.1029/2004JD005081. [full text]

Atmospheric visibility trends in an urban area in Taiwan 1961–2003 – Tsai (2005) “Climatological observations made in Tainan urban area, southern Taiwan, between 1961 and June 2003 were analyzed along with critical air pollutants monitored from 1994 to June 2003 in order to establish the relationship between atmospheric visibility and major air pollutants and meteorological parameters in the urban area. The visibility discrepancy between weekend and week days was also examined. Average annual visibility in the complete period 1961–2003 was 12.4±4.2 km. However, during the early 1960s it was >20 km, against only 6–7 km between 2002 and 2003. This study revealed a correlation between PM10 and NOx levels, which were higher on weekdays than on weekends, and low weekday visibility. Furthermore, decreased visibility was related mostly to increases in PM10. A weekend effect, in which weekend ozone concentrations exceed weekday concentrations, was also revealed. Mixing layer height is an most important meteorological parameter involved in visibility reduction. Principal component analysis demonstrated that increased vehicular emissions, road traffic dust and industrial activity markedly impacted visibility. Pollutant standard index (PSI) values >100 were characterized by concentrations of PM10 and NOx and atmospheric pressure higher than normal, but with wind speed lower than normal. Regression results for various empirical models of visibility demonstrated that higher PM10 concentrations implied lower visibility ranges, and the parameter of ln[PM10] represented the most significant impact on visibility. Because PM2.5 has a significant impact on visibility, a targeted reduction of PM10 would not completely improve the visual range. However, there is a strong association between presence of PM10 and presence of PM2.5, such that a targeted reduction in PM10 is likely to lead to an increase in visibility.” Ying I. Tsai, Atmospheric Environment, Volume 39, Issue 30, September 2005, Pages 5555-5567, doi:10.1016/j.atmosenv.2005.06.012.

Variations in the diurnal character of tropical cyclone wind speeds – Cerveny & Balling (2005) It is not mentioned in the abstract, but apparently they also found a weekly cycle in their data. “A significant decline in diurnal temperature range (DTR) is identified along the Atlantic seaboard. Recent studies suggest that DTR changes demonstrate a human-created weekly cycle and may therefore be anthropogenic. In this study, we address whether there is a change in the diurnal variation in Tropical Cyclone (TC) wind speeds that is consistent with the DTR trend over land. Our analysis of 34 years of TC activity reveals variations such that the difference between day and night wind speeds of TCs has decreased over time. Our work gives limited support to the contention that TC diurnal wind speed differences are thermally driven and, hence, warmer night temperatures (a smaller DTR over time) are leading to stronger nighttime winds over time. Our study initiates investigation of potential influences of climate changes (such as DTR) on secondary climatic phenomena.” Cerveny, R. S., and R. C. Balling Jr. (2005), Geophys. Res. Lett., 32, L06706, doi:10.1029/2004GL021177.

Observations of a “weekend effect” in diurnal temperature range – Forster & Solomon (2003) “Using surface measurements of maximum and minimum temperatures from the Global Daily Climatological Network data set, we find evidence of a weekly cycle in diurnal temperature range (DTR) for many stations in the United States, Mexico, Japan, and China. The “weekend effect,” which we define as the average DTR for Saturday through Monday minus the average DTR for Wednesday through Friday, can be as large as 0.5 K, similar to the magnitude of observed long-term trends in DTR. This weekend effect has a distinct large-scale pattern that has changed only slightly over time, but its sign is not the same in all locations. The station procedures and the statistical robustness of both the individual station data and the patterns of DTR differences are thoroughly examined. We conclude that the weekend effect is a real short time scale and large spatial scale geophysical phenomenon, which is necessarily human in origin. We thus provide strong evidence of an anthropogenic link to DTR, an important climate indicator. Several possible anthropogenic mechanisms are discussed; we speculate that aerosol-cloud interactions are the most likely cause of this weekend effect, but we do not rule out others.” Piers M. de F. Forster and Susan Solomon, PNAS September 30, 2003, vol. 100 no. 20 11225-11230, doi: 10.1073/pnas.2034034100. [full text]

Weekly cycle of NO2 by GOME measurements: a signature of anthropogenic sources – Beirle et al. (2003) “Nitrogen oxides (NO+NO2=NOx and reservoir species) are important trace gases in the troposphere with impact on human health, atmospheric chemistry and climate. Besides natural sources (lightning, soil emissions) and biomass burning, fossil fuel combustion is estimated to be responsible for about 50% of the total production of NOx. Since human activity in industrialized countries largely follows a seven-day cycle, fossil fuel combustion is expected to be reduced during weekends. This “weekend effect” is well known from local, ground based measurements, but has never been analysed on a global scale before. The Global Ozone Monitoring Experiment (GOME) on board the ESA-satellite ERS-2 allows measurements of NO2 column densities. By estimating and subtracting the stratospheric column, and considering radiative transfer, vertical column densities (VCD) of tropospheric NO2 can be determined (e.g. Leue et al., 2001). We demonstrate the statistical analysis of weekly cycles of tropospheric NO2 VCDs for different regions of the world. In the cycles of the industrialized regions and cities in the US, Europe and Japan a clear Sunday minimum of tropospheric NO2 VCD can be seen. Sunday NO2 VCDs are about 25-50% lower than working day levels. Metropolitan areas with other religious and cultural backgrounds (Jerusalem, Mecca) show different weekly patterns corresponding to different days of rest. In China, no weekly pattern can be found. The presence of a weekly cycle in the measured tropospheric NO2 VCD may help to identify the different anthropogenic source categories. Furthermore, we estimated the lifetime of tropospheric NO2 by analysing the mean weekly cycle exemplarily over Germany, obtaining a value of about 6 h in summer and 18-24 h in winter.” Beirle, S., Platt, U., Wenig, M., and Wagner, T., Atmos. Chem. Phys., 3, 2225-2232, doi:10.5194/acp-3-2225-2003, 2003. [full text]

A weekly cycle in atmospheric carbon dioxide – Cerveny & Coakley (2002) “We present a new statistic called the “Mean Symmetrized Residual” (MSR) for detection and quantification of a weekly cycle in measured daily atmospheric carbon dioxide (CO2). At the Mauna Loa Observatory in Hawaii, we conclude that CO2 concentrations, on average, are significantly lower (0.022 parts per million by volume, ppmv) on weekends (Saturday–Sunday) than during the rest of the week. Over the past twenty-five years, the variation of the mean values of MSR (as a function of day of the week) has been relatively stable. We speculate that the observed weekday/weekend variation in CO2 at Mauna Loa is the result of anthropogenic emissions on Hawaii and nearby sources. We do not detect a weekly cycle in daily CO2 concentration measured at South Pole, Antarctica. This methodology has applicability to a variety of datasets.” Cerveny, R. S., and K. J. Coakley (2002), Geophys. Res. Lett., 29(2), 1028, doi:10.1029/2001GL013952.

The influence of tropospheric ozone on the air temperature of the city of Toronto, Ontario, Canada – Beaney & Gough (2002) “Weekday/weekend variations in tropospheric ozone concentrations were examined to determine whether ground-level greenhouse gases have a significant impact on local climate. The city of Toronto, Canada, was chosen due to a high volume of commuter traffic and frequent exposure to high ozone episodes. Due to day-of-the-week variations in commuter traffic, ozone concentrations were shown to vary significantly between weekdays and weekends. During high ozone episodes weekend air temperatures were significantly higher than those observed on weekdays. As no meteorological phenomenon is known to occur over a 7 day cycle the observed temperature variations were attributed to anthropogenic activity.” Gary Beaney and William A. Gough, Atmospheric Environment, Volume 36, Issue 14, May 2002, Pages 2319-2325, doi:10.1016/S1352-2310(02)00184-X.

Spectral analysis of weekday–weekend differences in ambient ozone, nitrogen oxide, and non-methane hydrocarbon time series in California – Marr & Harley (2002) “We describe the history and spatial distribution of day-of-week differences in ambient ozone, NOx, and VOC concentrations through the analysis of two decades of measurements from sites located throughout California. Spectral analysis of the concentration time series shows that weekly patterns in ozone concentrations, typically with higher values of ozone on weekends, have become more widespread in California between 1980 and 1999. In contrast, a strong weekly pattern in NOx concentrations has been present throughout the entire period, and weekly patterns in VOC concentrations, though not as evident, have also been present during the entire 20-yr period. We examine 8-h average ozone concentrations, which appear to be a more sensitive measure of day-of-week differences in ozone than are 1-h averages. At sites with significant weekly cycles, fluctuations in pollutant concentrations that occur on a weekly time scale account for 6.6±3.5%, 3.0±1.7%, and 2.1±0.9% of the total variance in NOx, NMHC, and ozone concentrations, respectively. Concentrations of all three pollutants have been declining in most locations over the past 20 yr. Our results support the hypothesis that the weekend ozone effect is due to a combination of VOC-sensitivity and reduced NOx emissions on weekends. The spread of the weekend ozone effect may be due to a shift in ozone formation towards VOC-sensitivity, as control programs have reduced emissions of VOC more than NOx.” Linsey C. Marr and Robert A. Harley, Atmospheric Environment, Volume 36, Issue 14, May 2002, Pages 2327-2335, doi:10.1016/S1352-2310(02)00188-7.

Comparison between weekend and weekday ozone concentration in large cities in France – Pont & Fontan (2001) “This paper examines ozone data from five large French cities (Marseilles, Lyon, Paris, Strasbourg and Toulouse) in spring and summer over a three-year period to study the possible influence of local primary pollutant emissions. In these cities the level of traffic emission varies according to the day of the week. There is a decrease of about 25% in traffic emissions between non-consecutive Tuesdays and Sundays. Traffic emissions on Fridays are about 40% more than on non-consecutive Sundays whereas they seem to be similar for non-consecutive Tuesdays and Thursdays. Despite this variation in traffic emissions between Fridays and Sundays, 85% of daily ozone maxima are identical for all days compared; in 15% of cases, percentiles of daily ozone maxima vary by about 20% at the most. This difference is observed for the highest values of daily ozone maxima that we can find both in rural and urban sites. Marseilles is the most pollution-sensitive city; every site of this area is concerned, which gives a regional origin to ozone variability. In the less-populated Toulouse area, differences between ozone on Fridays and Sundays are less significant. Our results show the importance of advection phenomena of ozone. It calls into question strategies of local reductions in traffic during ozone episodes.” Véronique Pont and Jacques Fontan, Atmospheric Environment, Volume 35, Issue 8, 2001, Pages 1527-1535, doi:10.1016/S1352-2310(00)00308-3.

Weekly Precipitation Cycles along the Northeast Corridor? – DeLisi et al. (2001) “Twenty years of precipitation data from seven cities along or near the east coast of the United States from the northern mid-Atlantic region to northern New England have been analyzed to determine if there are any weekly cycles in either daily precipitation frequency or intensity. Any such weekly cycle could be considered evidence of anthropogenic influence on the climate of that region. Data were examined for each individual site and for all sites combined. The data were subjected to various statistical procedures, including one-way analysis of variance, Student’s t-test, and the chi-square goodness-of-fit test. Overall, results were not significant at the 95% confidence level. Thus, this study is unable to detect any weekly cycle in daily precipitation intensity or frequency.” DeLisi, Mark P., Alan M. Cope, Jason K. Franklin, 2001, Wea. Forecasting, 16, 343–353. [full text]

Spectral analysis of air pollutants. Part 1: elemental carbon time series – Hies et al. (2000) “An effective method to analyse different air pollution sources in an elemental carbon time series is presented. As a second feature, this technique allows a fast and efficient classification of monitoring sites. Time series of daily elemental carbon measurements at various urban locations have been evaluated with the corresponding power spectra. Typical and well-known periodicities caused by anthropogenic and meteorological influences have been identified using coherence and phase spectra. It will be shown that domestic heating by coal combustion appears as a 365 day periodicity, traffic contributes 3.5, 4.6 and 7 day peaks in the spectrum and elevated long range elemental carbon can be identified as characteristic peaks with periodicities in the range from 13 to 42 days. As the relative amplitudes of the various influences vary depending on the location of the measurement site in the urban area, the use of estimated power spectra helps to find the influence of traffic, domestic coal-heating and long range transport on the elemental carbon concentration.” Thomas Hies, Renate Treffeisen, Ludwig Sebald and Eberhard Reimer, Atmospheric Environment, Volume 34, Issue 21, 2000, Pages 3495-3502, doi:10.1016/S1352-2310(00)00146-1.

Comparisons of weekday–weekend ozone: importance of biogenic volatile organic compound emissions in the semi-arid southwest USA – Diem (2000) “This paper examines differences between daily maximum weekday and weekend ambient ozone concentrations in the Tucson, AZ metropolitan area. Temporal variations in the Weekend Effect (i.e. weekend ozone concentrations are larger than weekday concentrations) are not explained entirely by changes in anthropogenic emissions of ozone precursor chemicals (i.e. nitrogen oxides and volatile organic compounds). A dramatic change from the Weekend Effect in June to the Weekday Effect (i.e. weekday ozone concentrations are larger than weekend concentrations) in July is associated with the onset of the North American Monsoon. A transition from a relatively dry atmosphere during the arid foresummer months of May and June to a relatively moist atmosphere during the monsoon months of July and August seems to explain the changes in ozone concentrations. Moist conditions are associated with increases in biogenic volatile organic compound (BVOC) emissions in the urban forest and surrounding desert areas. BVOC emissions appear to be an important source of VOCs, especially during the monsoon months. Therefore, an increase in ambient BVOC concentrations from June to July presumably reverses the sensitivity of ozone production in the Tucson area from VOC- to NOx-sensitive.” Jeremy E. Diem, Atmospheric Environment, Volume 34, Issue 20, 2000, Pages 3445-3451, doi:10.1016/S1352-2310(99)00511-7.

Weekly cycles of air pollutants, precipitation and tropical cyclones in the coastal NW Atlantic region – Cerveny & Balling (1998) “Direct human influences on climate have been detected at local scales, such as urban temperature increases and precipitation enhancement, and at global scales. A possible indication of an anthropogenic effect on regional climate is by identification of equivalent weekly cycles in climate and pollution variables. Weekly cycles have been observed in both global surface temperature and local pollution data sets. Here we describe statistical analyses that reveal weekly cycles in three independent regional-scale coastal Atlantic data sets: lower-troposphere pollution, precipitation and tropical cyclones. Three atmospheric monitoring stations record minimum concentrations of ozone and carbon monoxide early in the week, while highest concentrations are observed later in the week. This air-pollution cycle corresponds to observed weekly variability in regional rainfall and tropical cyclones. Specifically, satellite-based precipitation estimates indicate that near-coastal ocean areas receive significantly more precipitation at weekends than on weekdays. Near-coastal tropical cyclones have, on average, significantly weaker surface winds, higher surface pressure and higher frequency at weekends. Although our statistical findings limit the identification of cause–effect relationships, we advance the hypothesis that the thermal influence of pollution-derived aerosols on storms may drive these weekly climate cycles.” Randall S. Cerveny & Robert C. Balling, Jr., Nature 394, 561-563 (6 August 1998) | doi:10.1038/29043. [full text]

Weekly cycle of meteorological variations in Melbourne and the role of pollution and anthropogenic heat release – Simmonds & Keay (1997) “An aspect of anthropogenic impacts on climate have been assessed by examining the day-of-the-week variation (DOWV) of important meteorological elements. The data used were those of daily maximum and minimum temperature and rainfall for Melbourne for the period 1856–1990. This long series has been broken up into five 27-yr subperiods to expose how any such variation has changed over the record. We find there to be no DOWV in the summer “half” of the year for any of the subperiods. The only statistically significant variations to have physical meaning occur in the winter of the most recent subperiod (1964–1990). In that time maximum temperature exhibits a significant (10% confidence level) DOWV and weekdays are 0.29°C warmer than weekends (5%). Minimum temperatures and rainfall amounts were also found to be greater (10% level) on weekdays by 0.24°C and 0.20 mm d−1, respectively. We have considered the possible impacts of day-of-the-week variation of atmospheric pollution loading and of the local generation of heat. We hypothesise that the magnitude of the contrast between weekday-weekend anthropogenic heat emissions is sufficient to explain the temperature differences and these in turn are consistent with the weekday excess of rainfall. This perspective is concordant with the results of many recent studies which stress the importance of anthropogenic heating.” Ian Simmonds and Kevin Keay, Atmospheric Environment, Volume 31, Issue 11, June 1997, Pages 1589-1603, doi:10.1016/S1352-2310(96)00344-5. [full text]

Weekend-weekday differences of near-surface ozone concentrations in Switzerland for different meteorological conditions – Brönnimann & Neu (1997) “Mean weekly cycles of daily ozone peak levels are extracted out of 8 yr data sets under selected meteorological conditions. In the region under study, the emissions of precursor substances are considerably lower on weekends than on weekdays, as can be derived from the Swiss emission inventory or from traffic frequencies. Chemical production as well as destruction of ozone are affected differently by sudden changes in emissions, depending on meteorology and on the structure of the emissions. Therefore, in Switzerland, several distinct patterns of the weekly cycle of mean daily ozone peak concentrations can be detected. When meteorology is not favourable to ozone production, weekends show generally higher ozone peaks than weekdays. Favourable meteorology (i.e. high solar radiation, high temperatures, low wind speeds) produces an inverse pattern, the mean ozone peaks being 10–15% lower on Sundays than on Thursdays or Fridays. Differences in emission structures slightly modify the patterns and can delay the effects. Threshold values to separate favourable conditions can be estimated for radiation and temperature. In Switzerland, “favourable” meteorology is achieved on about 30–50 days per year, corresponding well with “summer smog days”.” Stefan Brönnimann and Urs Neu, Atmospheric Environment, Volume 31, Issue 8, April 1997, Pages 1127-1135, doi:10.1016/S1352-2310(96)00311-1.

C2—C6 hydrocarbon measurements at four rural locations across Canada – Bottenheim & Shepherd (1995) “Observations of low molecular weight hydrocarbons at four rural locations in Canada are reported. The measurements cover a period of one year (1991), and the seasonal trends are discussed. It is deduced that most variation is due to photochemically driven processes (OH chemistry). Although at least two of the sites were well removed from large urban source regions, the observations show a clear anthropogenic influence on the rural hydrocarbon levels at all sites. Air mass back-trajectories have been used to investigate the origin of the observed hydrocarbons. Weekday/weekend effects are distinguishable at two of the sites, and correlation with a limited set of CO observations at one of the sites is found to be very good for those compounds that are known to originate from transportation related processes. Comparison of the data with published observations suggests that the background distribution of hydrocarbons over the North American continent is quite homogeneous. Isoprene is the only hydrocarbon of biogenic origin that was measured in this study, and its importance relative to the other measured compounds with respect to photochemical processes is indicated.” Jan W. Bottenheim and Marjorie F. Shepherd, Atmospheric Environment, Volume 29, Issue 6, 1995, Pages 647-664, doi:10.1016/1352-2310(94)00318-F.

Weekdays warmer than weekends? – Gordon (1994) No abstract available, but is described in Bäumer et al. (2008): “Gordon (1994) found a significant but very small weekly temperature cycle for the northern hemisphere for the period 1979–1992.” A. H. Gordon, Nature 367, 325 – 326 (27 January 1994); doi:10.1038/367325b0.

Photochemistry of the “Sunday Effect” – Graedel et al. (1977) No abstract available, but apparently finds a weekly cycle from pollution data sets. Thomas E. Graedel, Leonilda A. Farrow, Thomas A. Weber, Environ. Sci. Technol., 1977, 11 (7), pp 690–694, DOI: 10.1021/es60130a005.

A comparison of weekend-weekday ozone and hydrocarbon concentrations in the Baltimore-Washington metropolitan area – Lebron (1975) “A “smog index”, related to dosage (ppm-h) of ozone, was derived. Indices were calculated using data from the Baltimore-Washington metropolitan area for the months of June–September of 1972 and 1973. On the average, weekends had higher indices than weekdays, although this difference may not be statistically significant. Further analysis of the data indicates that 06:00–09:00 h average concentrations of non-methane hydrocarbons are significantly higher during weekdays than during weekends and no relationship exists between these morning hydrocarbon levels and the afternoon peak ozone concentration. These results place some doubt on the effectiveness of early morning hydrocarbon emission control alone in an abatement program for photochemical oxidants.” Felipe Lebron, Atmospheric Environment, Volume 9, Issue 9, September 1975, Pages 861-863, doi:10.1016/0004-6981(75)90046-3.

Sunday and Workday Variations in Photochemical Air Pollutants in New Jersey and New York – Cleveland et al. (1974) “Concentration distributions of air contaminants and meteorological variables in New Jersey and New York for workdays (Mondays through Fridays, omitting holidays) and Sundays are compared by means of quantile-quantile plots. The ozone distributions are slightly higher on Sundays, and the primary pollutant distributions are lower. These results raise serious questions about the validity of current concepts underlying ozone reduction in urban atmospheres.” W. S. Cleveland, T. E. Graedel, B. Kleiner and J. L. Warner, Science 13 December 1974, Vol. 186 no. 4168 pp. 1037-1038, DOI: 10.1126/science.186.4168.1037.

Note on the effect of the weekly cycle of air pollution on solar radiation at Toronto – Mateer (1961) Int J Air Water Pollut. 1961 Jun;4:52-4.

Posted in AGW evidence | 4 Comments »

New research from last week 52/2010

Posted by Ari Jokimäki on January 3, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Weekly cycle in Spanish CO2 measurements

Persistence analysis of CO2 concentrations recorded at a rural site in the upper Spanish plateau – Pérez et al. (2010) “Persistence of CO2 daily means recorded at a rural site over three years was analysed using three procedures: the ST method, rescaled range analysis and detrended fluctuation analysis. Four series were previously considered, since the original series was detrended and gaps were filled. The detrending procedure comprised four steps: a linear evolution of about 3 ppm per year, a quadratic function with a maximum yearly range of 11 ppm, and two harmonic functions, the first with yearly and semi-yearly cycles and the second with a weekly cycle. Yearly ranges of both functions increased with time, their maxima being about 5 and 2 ppm, respectively. Gaps were filled with a method based on previous observation and a Gaussian function, whose standard deviation was fitted so as to resemble original data. The ST method proved extremely sensitive to the detrending procedure. A detailed analysis of the Hurst exponent allowed us to establish four regions where persistence gradually decreased. Finally, detrended fluctuation analysis provided a similar result to rescaled range analysis. From these methods, persistence was high in an interval of about three weeks.” Isidro A. Pérez, M. Luisa Sánchez, M. Ángeles García and Vanessa Paredes, Atmospheric Research, 2010, doi:10.1016/j.atmosres.2010.12.025.

Mankind affected atmospheric CO2 already 3000 years ago

Holocene carbon emissions as a result of anthropogenic land cover change – Kaplan et al. (2010) “Humans have altered the Earth’s land surface since the Paleolithic mainly by clearing woody vegetation first to improve hunting and gathering opportunities, and later to provide agricultural cropland. In the Holocene, agriculture was established on nearly all continents and led to widespread modification of terrestrial ecosystems. To quantify the role that humans played in the global carbon cycle over the Holocene, we developed a new, annually resolved inventory of anthropogenic land cover change from 8000 years ago to the beginning of large-scale industrialization (AD 1850). This inventory is based on a simple relationship between population and land use observed in several European countries over preindustrial time. Using this data set, and an alternative scenario based on the HYDE 3.1 land use data base, we forced the LPJ dynamic global vegetation model in a series of continuous simulations to evaluate the impacts of humans on terrestrial carbon storage during the preindustrial Holocene. Our model setup allowed us to quantify the importance of land degradation caused by repeated episodes of land use followed by abandonment. By 3 ka BP, cumulative carbon emissions caused by anthropogenic land cover change in our new scenario ranged between 84 and 102 Pg, translating to c. 7 ppm of atmospheric CO2. By AD 1850, emissions were 325–357 Pg in the new scenario, in contrast to 137–189 Pg when driven by HYDE. Regional events that resulted in local emissions or uptake of carbon were often balanced by contrasting patterns in other parts of the world. While we cannot close the carbon budget in the current study, simulated cumulative anthropogenic emissions over the preindustrial Holocene are consistent with the ice core record of atmospheric δ13CO2 and support the hypothesis that anthropogenic activities led to the stabilization of atmospheric CO2 concentrations at a level that made the world substantially warmer than it otherwise would be.” Jed O. Kaplan, Kristen M. Krumhardt, Erle C. Ellis, William F. Ruddiman, Carsten Lemmen, Kees Klein Goldewijk, The Holocene, December 30, 2010, doi: 10.1177/0959683610386983. [full text]

Freshwater measurements from East Greenland Current

Interannual variability of Arctic sea ice export into the East Greenland Current – Cox et al. (2010) “Observations since the 1950s suggest that the Arctic climate system is changing in response to rising global air temperatures. These changes include an intensified hydrological cycle, Arctic sea ice decline, and increasing Greenland glacial melt. Here we use new δ18O data from the East Greenland Current system at Cape Farewell and Denmark Strait to determine the relative proportions of the freshwater components within the East Greenland Current and East Greenland Coastal Current. Through the comparison of these new data with historical studies, we gain insight into the changing Arctic freshwater balance. We detect three key shifts in the net freshwater component δ18O values, these are (1) a shift to lighter values in the late 1990s that possibly indicates an increased Greenland glacial melt or a reduced sea ice melt admixture and (2) a short-term shift to a ∼10‰ heavier value in 2005 followed by (3) a shift back to the historic average value in 2008. The latter fluctuation reflects a short-term dramatic rise and fall of sea ice meltwater addition into the East Greenland Current system. We infer that this anomalously large inclusion of sea ice meltwater resulted from a short-term peak in Arctic sea ice export via Fram Strait. Our findings, therefore, suggest that the freshwater carried in the East Greenland Current system is susceptible to short-term, high-amplitude changes in the upstream freshwater balance, which may have important ramifications for the global thermohaline circulation through the suppression of deep water formation in the North Atlantic.” Cox, K. A., J. D. Stanford, A. J. McVicar, E. J. Rohling, K. J. Heywood, S. Bacon, M. Bolshaw, P. A. Dodd, S. De la Rosa, and D. Wilkinson (2010), J. Geophys. Res., 115, C12063, doi:10.1029/2010JC006227.

Rocket science – black carbon emissions

Potential climate impact of black carbon emitted by rockets – Ross et al. (2010) “A new type of hydrocarbon rocket engine is expected to power a fleet of suborbital rockets for commercial and scientific purposes in coming decades. A global climate model predicts that emissions from a fleet of 1000 launches per year of suborbital rockets would create a persistent layer of black carbon particles in the northern stratosphere that could cause potentially significant changes in the global atmospheric circulation and distributions of ozone and temperature. Tropical stratospheric ozone abundances are predicted to change as much as 1%, while polar ozone changes by up to 6%. Polar surface temperatures change as much as one degree K regionally with significant impacts on polar sea ice fractions. After one decade of continuous launches, globally averaged radiative forcing from the black carbon would exceed the forcing from the emitted CO2 by a factor of about 105 and would be comparable to the radiative forcing estimated from current subsonic aviation.” Ross, M., M. Mills, and D. Toohey (2010), Geophys. Res. Lett., 37, L24810, doi:10.1029/2010GL044548.

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2010 – First full year of AGW Observer

Posted by Ari Jokimäki on January 2, 2011

I made the first post of this blog in July 28, 2009, so the 2010 was the first full year of AGW Observer. What has happened here during the first year (and a half)?

161 posts and 567 comments have happened, but there’s more in the details:


The main attraction here has of course been the paperlists. The biological indicators of global warming was the subject of my first paperlist. When I was creating the paperlists at early stage I had no idea if they would be appreciated by many. I just made the lists because I had a need for them so I originally made them as a resource for myself. By now it is clear that the lists are quite widely appreciated.

It also became clear that I had no idea which lists would be popular. When looking at the evidence for the anthropogenic global warming, to me the most compelling evidence comes from the direct measurements from the atmosphere. Based on that, I thought that my lists on the observed changes in outgoing longwave radiation and in downward longwave radiation would be the most popular ones. Those two are relatively popular lists but clearly the most popular list so far has been the “Papers on laboratory measurements of CO2 absorption properties”.

I was quite surprised when I realised that the laboratory measurement list was by far the most popular of my lists. I originally thought of it as just a curiosity – just something to show that we also have done the basic science on these issues in labs too, while really looking at the OLR and DLR measurements with more interest. But it turned out that the laboratory studies were just what doctor ordered. This list is cited continuously and frequently in Internet discussions. In my blog statistics I can see when someone gives a link to my blog and I do click the links to see what kind of use my lists have. When following those links it becomes obvious that the laboratory paperlist is the most cited one, probably almost half of the citations are to this list.

Top ten lists at the moment are:

1. Papers on laboratory measurements of CO2 absorption properties
2. Papers on climate sensitivity estimates
3. Papers on the Milankovitch cycles and climate
4. Papers on water vapor feedback observations
5. Papers on changes in OLR due to GHG’s
6. Papers on the non-significant role of cosmic rays in climate
7. Papers on the theory of CO2 absorption properties
8. Papers on Earth’s radiation budget
9. Papers on global cloud cover trends
10. Papers on tropical troposphere hotspot

I thank all the scientists who made the studies and wrote the research articles for me so I could include them to my lists.

Other articles

I haven’t written many articles as I have concentrated more on the paperlists. Two of my articles clearly stand out as most popular:

1. Comments on Lindzen & Choi (2009)
2. Unchallenging Copenhagen Climate Challenge

Traffic providers

I’m very bad and lazy in advertising myself. Fortunately, many have been kind enough to give links to my site. My blog is included in the blogrolls of quite many blogs. Some people have also mentioned my blog in their articles. My blog is also every once in a while mentioned in online discussions. Many would deserve a mention by name here for being particularly active in linking to my blog, but as I’m probably not aware of everyone active in this sense, I’m just making these general statements. However, my statistics do show where I get most traffic, so I’ll provide a list of places bringing me most traffic:

1. Skeptical Science – John Cook has included links to my paperlists in several of his articles.
2. RealClimate – Here the traffic comes from the discussions.
3. Tiede – Finnish popular science magazine. The traffic comes from their discussion forum which unfortunately seems to be badly infected by climate change deniers and conspiracy theorists.
4. Tuukka Simonen’s blog – A fellow Finnish climate blogger who has my site in his blogroll.
5. Rabett Run – Eli Rabett was one of the people who noticed my site at very early phase.
6. Gaia – Kaj Luukko’s Finnish blog about climate and energy related issues. Kaj also writes with me in our group-blog, the Ilmastotieto.
7. CO2-raportti – Finnish news site that also publishes some of my articles. Here the traffic is originating from the discussions.
8. Doskonale Szare – Climate blog from Poland having my site in blogroll. It’s nice to see that I have readers from all over the world.
9. Only In It For The Gold – My site is in the blogroll.
10. Google reader.
11. As the previous entry wasn’t a single site as such, we’ll take a honorary 11th place here as well. This is actually several blogs collected under a single heading. Some traffic here is coming from discussions at Deltoid and Stoat, but most of it is from A Few Things Illconsidered who include my postings to their weekly news.

I thank everyone who has ever directed or at least tried to direct some traffic here.

Quite a lot of my traffic comes from search engines. Here’s the top ten traffic giving search words for my site:

1. “agw observer” (and also “agwobserver”)
2. “agw”
3. “1500 year climate cycle”
4. “temperature 100 meters below the earth’s surface”
5. “polar bear populations”
6. “co2 absorption”
7. “underground temperatures”
8. “ocean heat content”
9. “co2 absorption spectrum”
10. “stratosphere temperature”

AGW Observer as traffic provider

Of all the links I have provided in my site, here are the 10 most clicked ones:

1. It’s good that I can offer John some (but only some) of the traffic back he has directed here.
2. Let me first take the opportunity here to give feedback to ScienceDirect: Dear ScienceDirect, could you please do something for your article URL’s? I know that I can dig up some shortened versions of the links (the DOI link for example), but it would be so much easier if I could just copy/paste a nice short URL from the address bar of my browser. Other places providing science articles have no trouble in providing compact URL’s. Thanks. It was rather surprising to see this paper by Toth et al. being clicked so much as it doesn’t appear to be that important for the questions being discussed here.
3. Same comment as in 1.
4. Deep Climate – this site really deserves the traffic.
5. Same comment as in 1.
6. I think for Deltoid I give more traffic than get.
7. Open Mind – great place to direct some traffic to.
8. “Sorry, your request could not be processed because the format of the URL was incorrect. Contact the Help Desk if the problem persists. [SD-001] “. Ouch. I better check what this is about.
9. Climate Denial Crock of the Week – has my site in blogroll but it seems that I have (so far) given more traffic than gotten.
10. Climate Change – I really enjoy Chris Colose’s articles.

Other things

I wish everyone enjoyable year 2011!

Posted in General | 4 Comments »

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