AGW Observer

Observations of anthropogenic global warming

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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