AGW Observer

Observations of anthropogenic global warming

New research from last week 50/2011

Posted by Ari Jokimäki on December 19, 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.

Developing methods for model performance comparison with observations

On the observational assessment of climate model performance – Annan et al. (2011) “Comparison of model outputs with observations of the climate system forms an essential component of model assessment and is crucial for building our confidence in model predictions. Methods for undertaking this comparison are not always clearly justified and understood. Here we show that the popular approach of comparing the ensemble spread to a so-called “observationally-constrained pdf” can be highly misleading. Such a comparison will almost certainly result in disagreement, but in reality tells us little about the performance of the ensemble. We present an alternative approach, and show how it may lead to very different, and rather more encouraging, conclusions. We additionally present some necessary conditions for an ensemble (or more generally, a probabilistic prediction) to be challenged by an observation.” Annan, J. D., J. C. Hargreaves, and K. Tachiiri (2011), Geophys. Res. Lett., 38, L24702, doi:10.1029/2011GL049812.

Revealing annual ice core layers from Eemian interglacial

Annual layering in the NGRIP ice core during the Eemian – Svensson et al. (2011) “The Greenland NGRIP ice core continuously covers the period from present day back to 123 ka before present, which includes several thousand years of ice from the previous interglacial period, MIS 5e or the Eemian. In the glacial part of the core, annual layers can be identified from impurity records and visual stratigraphy, and stratigraphic layer counting has been performed back to 60 ka. In the deepest part of the core, however, the ice is close to the pressure melting point, the visual stratigraphy is dominated by crystal boundaries, and annual layering is not visible to the naked eye. In this study, we apply a newly developed setup for high-resolution ice core impurity analysis to produce continuous records of dust, sodium and ammonium concentrations as well as conductivity of melt water. We analyzed three 2.2 m sections of ice from the Eemian and the glacial inception. In all of the analyzed ice, annual layers can clearly be recognized, most prominently in the dust and conductivity profiles. Part of the samples is, however, contaminated in dust, most likely from drill liquid. It is interesting that the annual layering is preserved despite a very active crystal growth and grain boundary migration in the deep and warm NGRIP ice. Based on annual layer counting of the new records, we determine a mean annual layer thickness close to 11 mm for all three sections, which, to first order, confirms the modeled NGRIP time scale (ss09sea). The counting does, however, suggest a longer duration of the climatically warmest part of the NGRIP record (MIS5e) of up to 1 ka as compared to the model estimate. Our results suggest that stratigraphic layer counting is possible basically throughout the entire NGRIP ice core, provided sufficiently highly-resolved profiles become available.” Svensson, A., Bigler, M., Kettner, E., Dahl-Jensen, D., Johnsen, S., Kipfstuhl, S., Nielsen, M., and Steffensen, J. P., Clim. Past, 7, 1427-1437, doi:10.5194/cp-7-1427-2011, 2011. [Full text]

Assessment of Southern Hemisphere paleoclimate records

Southern Hemisphere high-resolution palaeoclimate records of the last 2000 years – Neukom & Gergis (2011) “This study presents a comprehensive assessment of high-resolution Southern Hemisphere (SH) paleoarchives covering the last 2000 years. We identified 174 monthly to annually resolved climate proxy (tree ring, coral, ice core, documentary, speleothem and sedimentary) records from the Hemisphere. We assess the interannual and decadal sensitivity of each proxy record to large-scale circulation indices from the Pacific, Indian and Southern Ocean regions over the twentieth century. We then analyse the potential of this newly expanded palaeoclimate network to collectively represent predictands (sea surface temperature, sea level pressure, surface air temperature and precipitation) commonly used in climate reconstructions. The key dynamical centres-of-action of the equatorial Indo-Pacific are well captured by the palaeoclimate network, indicating that there is considerable reconstruction potential in this region, particularly in the post AD 1600 period when a number of long coral records are available. Current spatiotemporal gaps in data coverage and regions where significant potential for future proxy collection exists are discussed. We then highlight the need for new and extended records from key dynamical regions of the Southern Hemisphere. Although large-scale climate field reconstructions for the SH are in their infancy, we report that excellent progress in the development of regional proxies now makes plausible estimates of continental- to hemispheric-scale climate variations possible.” Raphael Neukom, Joëlle Gergis, The Holocene December 16, 2011 0959683611427335, doi: 10.1177/0959683611427335.

Warmer climate makes heavy rain heavier and more frequent and weak rain weaker and less frequent

Mechanisms for global warming impacts on rainfall frequency and intensity – Chou et al. (2011) “Global warming mechanisms that cause changes in frequency and intensity of precipitation in the tropics are examined in climate model simulations. Under global warming, tropical precipitation tends to be more frequent and intense for heavy precipitation, but becomes less frequent and weaker for light precipitation. Changes in precipitation frequency and intensity are both controlled by thermodynamic and dynamic components. The thermodynamic component is induced by changes in atmospheric water vapor, while the dynamic component is associated with changes in vertical motion. A set of equations is derived to estimate both thermodynamic and dynamic contributions to changes in frequency and intensity of precipitation, especially for heavy precipitation. In the thermodynamic contribution, increased water vapor reduces the magnitude of the required vertical motion to generate the same strength of precipitation, so precipitation frequency increases. Increased water vapor also intensifies precipitation due to the enhancement of water vapor availability in the atmosphere. In the dynamic contribution, the more stable atmosphere tends to reduce the frequency and intensity of precipitation, except for the heaviest precipitation. The dynamic component strengthens the heaviest precipitation in most climate model simulations, possibly due to a positive convective feedback.” Chia Chou, Chao-An Chen, Pei-Hua Tan, Kuan Ting Chen, Journal of Climate 2011, doi: http://dx.doi.org/10.1175/JCLI-D-11-00239.1.

We know how Greenland outlet glaciers respond to warming but how they respond to cooling?

Response of a marine-terminating Greenland outlet glacier to abrupt cooling 8200 and 9300 years ago – Young et al. (2011) “Long-term records of Greenland outlet-glacier change extending beyond the satellite era can inform future predictions of Greenland Ice Sheet behavior. Of particular relevance is elucidating the Greenland Ice Sheet’s response to decadal- and centennial-scale climate change. Here, we reconstruct the early Holocene history of Jakobshavn Isbræ, Greenland’s largest outlet glacier, using 10Be surface exposure ages and 14C-dated lake sediments. Our chronology of ice-margin change demonstrates that Jakobshavn Isbræ advanced to deposit moraines in response to abrupt cooling recorded in central Greenland ice cores ca. 8,200 and 9,300 years ago. While the rapid, dynamically aided retreat of many Greenland outlet glaciers in response to warming is well documented, these results indicate that marine-terminating outlet glaciers are also able to respond quickly to cooling. We suggest that short lag times of high ice flux margins enable a greater magnitude response of marine-terminating outlets to abrupt climate change compared to their land-terminating counterparts.” Young, N. E., J. P. Briner, Y. Axford, B. Csatho, G. S. Babonis, D. H. Rood, and R. C. Finkel (2011), Geophys. Res. Lett., 38, L24701, doi:10.1029/2011GL049639.

The rise but not fall of Taku Glacier late summer transient snowline

Utility of late summer transient snowline migration rate on Taku Glacier, Alaska – Pelto (2011) “On Taku Glacier, Alaska a combination of field observations of snow water equivalent (SWE) from snowpits and probing in the vicinity of the transient snowline (TSL) are used to quantify the mass balance gradient. The balance gradient derived from the TSL and SWE measured in snowpits at 1000 m from 1998–2010 ranges from 2.6–3.8 mm m−1. Probing transects from 950 m–1100 m directly measure SWE and yield a slightly higher balance gradient of 3.3–3.8 mm m−1. The TSL on Taku Glacier is identified in MODIS and Landsat 4 and 7 Thematic Mapper images for 31 dates during the 2004–2010 period to assess the consistency of its rate of rise and reliability in assessing ablation for mass balance assessment. For example, in 2010, the TSL was 750 m on 28 July, 800 m on 5 August, 875 m on 14 August, 925 m on 30 August, and 975 m on 20 September. The mean observed probing balance gradient was 3.3 mm m−1, combined with the TSL rise of 3.7 m day−1 yields an ablation rate of 12.2 mm day−1 from mid-July to mid-Sept, 2010. The TSL rise in the region from 750–1100 m on Taku Glacier during eleven periods each covering more than 14 days during the ablation season indicates a mean TSL rise of 3.7 m day−1, the rate of rise is relatively consistent ranging from 3.1 to 4.4 m day−1. This rate is useful for ascertaining the final ELA if images or observations are not available near the end of the ablation season. The mean ablation from 750–1100 m during the July–September period determined from the TSL rise and the observed balance gradient is 11–13 mm day−1 on Taku Glacier during the 2004–2010 period. The potential for providing an estimate of bn from TSL observations late in the melt season from satellite images combined with the frequent availability of such images provides a means for efficient mass balance assessment in many years and on many glaciers.” Pelto, M., The Cryosphere, 5, 1127-1133, doi:10.5194/tc-5-1127-2011, 2011. [Full text]

Review article on North Atlantic Oscillation

Past and recent changes in the North Atlantic oscillation – Pinto & Raible (2011) “The North Atlantic oscillation (NAO) is under current climate conditions the leading mode of atmospheric circulation variability over the North Atlantic region. While the pattern is present during the entire year, it is most important during winter, explaining a large part of the variability of the large-scale pressure field, being thus largely determinant for the weather conditions over the North Atlantic basin and over Western Europe. In this study, a review of recent literature on the basic understanding of the NAO, its variability on different time scales and driving physical mechanisms is presented. In particular, the observed NAO variations and long-term trends are put into a long term perspective by considering paleo-proxy evidence. A representative number of recently released NAO reconstructions are discussed. While the reconstructions agree reasonably well with observations during the instrumental overlapping period, there is a rather high uncertainty between the different reconstructions for the pre-instrumental period, which leads to partially incoherent results, that is, periods where the NAO reconstructions do not agree even in sign. Finally, we highlight the future need of a broader definition of the NAO, the assessment of the stability of the teleconnection centers over time, the analysis of the relations to other relevant variables like temperature and precipitation, as well as on the relevant processes involved.” Joaquim G. Pinto, Christoph C. Raible, Wiley Interdisciplinary Reviews: Climate Change, DOI: 10.1002/wcc.150.

New review article looks at geological fakes and frauds

Geological Fakes and Frauds – Ruffell et al. (2011) “Some geological fakes and frauds are carried out solely for financial gain (mining fraud), whereas others maybe have increasing aesthetic appeal (faked fossils) or academic advancement (fabricated data) as their motive. All types of geological fake or fraud can be ingenious and sophisticated, as demonstrated in this article. Fake gems, faked fossils and mining fraud are common examples where monetary profit is to blame: nonetheless these may impact both scientific theory and the reputation of geologists and Earth scientists. The substitution or fabrication of both physical and intellectual data also occurs for no direct financial gain, such as career advancement or establishment of belief (e.g. evolution vs. creationism). Knowledge of such fakes and frauds may assist in spotting undetected geological crimes: application of geoforensic techniques helps the scientific community to detect such activity, which ultimately undermines scientific integrity.” Alastair Ruffell, Niall Majury, William E. Brooks, Earth-Science Reviews, doi:10.1016/j.earscirev.2011.12.001.

Moon affects the weather

Monthly lunar declination extremes’ influence on tropospheric circulation patterns – Krahenbuhl et al. (2011) “Short-term tidal variations occurring every 27.3 days from southern (negative) to northern (positive) maximum lunar declinations (MLDs), and back to southern declination of the moon have been overlooked in weather studies. These short-term MLD variations’ significance is that when lunar declination is greatest, tidal forces operating on the high latitudes of both hemispheres are maximized. We find that such tidal forces deform the high latitude Rossby longwaves. Using the NCEP/NCAR reanalysis data set, we identify that the 27.3 day MLD cycle’s influence on circulation is greatest in the upper troposphere of both hemispheres’ high latitudes. The effect is distinctly regional with high impact over central North America and the British Isles. Through this lunar variation, midlatitude weather forecasting for two-week forecast periods may be significantly improved.” Krahenbuhl, D. S., M. B. Pace, R. S. Cerveny, and R. C. Balling Jr. (2011), J. Geophys. Res., 116, D23121, doi:10.1029/2011JD016598.

Climate change makes some interacting species drift apart

Increasing range mismatching of interacting species under global change is related to their ecological characteristics – Schweiger et al. (2011) “Aim: We investigate the importance of interacting species for current and potential future species distributions, the influence of their ecological characteristics on projected range shifts when considering or ignoring interacting species, and the consistency of observed relationships across different global change scenarios. Location: Europe. Methods: We developed ecological niche models (generalized linear models) for 36 European butterfly species and their larval host plants based on climate and land-use data. We projected future distributional changes using three integrated global change scenarios for 2080. Observed and projected mismatches in potential butterfly niche space and the niche space of their hosts were first used to assess changing range limitations due to interacting species and then to investigate the importance of different ecological characteristics. Results: Most butterfly species were primarily limited by climate. Species dwelling in warm areas of Europe and tolerant to large variations in moisture conditions were projected to suffer less from global change. However, a gradient from climate to host plant control was apparent, reflecting the range size of the hosts. Future projections indicated increased mismatching of already host-plant-limited butterflies and their hosts. Butterflies that utilize plants with restricted ranges were projected to suffer most from global change. The directions of these relationships were consistent across the scenarios but the level of spatial mismatching of butterflies and their host plants increased with the severity of the scenario. Main conclusions: Future changes in the co-occurrence of interacting species will depend on political and socio-economic development, suggesting that the composition of novel communities due to global change will depend on the way we create our future. A better knowledge of ecological species characteristics can be utilized to project the future fate and potential risk of extinction of interacting species leading to a better understanding of the consequences of changing biotic interactions. This will further enhance our abilities to assess and mitigate potential negative effects on ecosystem functions and services.” Oliver Schweiger, Risto K. Heikkinen, Alexander Harpke, Thomas Hickler, Stefan Klotz, Otakar Kudrna, Ingolf Kühn, Juha Pöyry, Josef Settele, Global Ecology and Biogeography, Special Issue: QUO VADIS, ECOSYSTEM? SCENARIOS AS A TOOL FOR LARGE-SCALE ECOLOGICAL RESEARCH, Volume 21, Issue 1, pages 88–99, January 2012, DOI: 10.1111/j.1466-8238.2010.00607.x. [Full text]

When climate warms California valley oaks gather around water bodies

Predicting species responses to climate change: demography and climate microrefugia in California valley oak (Quercus lobata) – Mclaughlin & Zavaleta (2011) “Anticipating species movement under climate change is a major focus in conservation. Bioclimate models are one of the few predictive tools for adaptation planning, but are limited in accounting for (1) climatic tolerances in pre-adult life stages that are potentially more vulnerable to warming; and (2) local-scale movement and use of climatic refugia as an alternative or complement to large-scale changes in distribution. To assess whether these shortfalls can be addressed with field demographic data, we used California valley oak (Quercus lobata Nee), a long-lived species with juvenile life stages known to be sensitive to climate. We hypothesized that the valley oak bioclimate model, based on adults, would overpredict the species’ ability to remain in the projected persisting area, due to higher climate vulnerability of young life stages; and underpredict the potential for the species to remain in the projected contracting area in local-scale refugia. We assessed the bioclimate model projections against actual demographic patterns in natural populations. We found that saplings were more constricted around surface water than adults in the projected contracting area. We also found that the climate envelope for saplings is narrower than that for adults. Saplings disappeared at a summer maximum temperature 3 degrees C below that associated with adults. Our findings indicate that rather than a complete shift northward and upward, as predicted by the species bioclimate model, valley oaks are more likely to experience constriction around water bodies, and eventual disappearance from areas exceeding a threshold of maximum temperature. Ours is the first study we know of to examine the importance of discrete life stage climate sensitivities in determining bioclimate modeling inputs, and to identify current climate change-related constriction of a species around microrefugia. Our findings illustrate that targeted biological fieldwork can be central to understanding climate change-related movement for long-lived, sessile species.” B.C. Mclaughlin, E.S. Zavaleta, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02630.x.

There’s a general warming trend over western North America

Climatic changes in western North America, 1950–2005 – Booth et al. (2011) “The rate of climatic change over western North America (WNA) is quantified for 485 climate stations for the period 1950–2005. Additionally, six stations with quality long-term records were selected and analysed for the period 1906–2005. The indicators used were developed by the World Meteorological Organization (WMO) and the World Climate Research Program’s Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI). From the 27 core indices, 4 temperature-based and 4 precipitation-based indicators were selected for in-depth analysis. The 8 million km2 study area is comprised of the 22 contiguous US states and 4 Canadian provinces west of the Mississippi River and Great Lakes. The results were divided into six general regions for interpretation and presentation. GIS interpolation of station-specific statistical output was completed to further aid in the identification of spatially coherent trends across WNA. Mean slopes were calculated over the whole study area, and by region, for each index, and then tested to determine if they were significantly different from zero. Results of the study show statistically significant historical climate trends across the study area. As expected in a region as geographically diverse as WNA, results differed between, and within, regions. Overall, temperature-based indicators showed a general warming trend over the entire study area, with the greatest increases along the North American Cordillera. The trends in precipitation-based indicators were more varied. General trends indicate moderately increasing precipitation volume and intensity over much of WNA. The strongest precipitation trends were found in areas with climate largely controlled by air masses originating over the Gulf of Mexico.” Evan L. J. Booth, James M. Byrne, Dan L. Johnson, International Journal of Climatology, DOI: 10.1002/joc.3401.

Climate warms but hot spell mortality declines in Czech Republic

Declining impacts of hot spells on mortality in the Czech Republic, 1986–2009: adaptation to climate change? – Kyselý & Plavcová (2011) “The study examines temporal changes in mortality associated with spells of large positive temperature anomalies (hot spells) in extended summer season in the population of the Czech Republic (Central Europe) during 1986–2009. Declining trends in the mortality impacts are found in spite of rising temperature trends. The finding remains unchanged if possible confounding effects of within-season acclimatization to heat and the mortality displacement effect are taken into account. Recent positive socioeconomic development, following the collapse of communism in Central and Eastern Europe in 1989, and better public awareness of heat-related risks are likely the primary causes of the declining vulnerability. The results suggest that climate change may have relatively little influence on heat-related deaths, since changes in other factors that affect vulnerability of the population are dominant instead of temperature trends. It is essential to better understand the observed nonstationarity of the temperature-mortality relationship and the role of adaptation and its limits, both physiological and technological, and to address associated uncertainties in studies dealing with climate change projections of temperature-related mortality.” Jan Kyselý and Eva Plavcová, Climatic Change, DOI: 10.1007/s10584-011-0358-4.

Frequency of extremely high temperatures has increased 10-fold since early 20th century

Climate change: a new metric to measure changes in the frequency of extreme temperatures using record data – Munasinghe et al. (2011) “Consensus on global warming is the result of multiple and varying lines of evidence, and one key ramification is the increase in frequency of extreme climate events including record high temperatures. Here we develop a metric—called “record equivalent draws” (RED)—based on record high (low) temperature observations, and show that changes in RED approximate changes in the likelihood of extreme high (low) temperatures. Since we also show that this metric is independent of the specifics of the underlying temperature distributions, RED estimates can be aggregated across different climates to provide a genuinely global assessment of climate change. Using data on monthly average temperatures across the global landmass we find that the frequency of extreme high temperatures increased 10-fold between the first three decades of the last century (1900–1929) and the most recent decade (1999–2008). A more disaggregated analysis shows that the increase in frequency of extreme high temperatures is greater in the tropics than in higher latitudes, a pattern that is not indicated by changes in mean temperature. Our RED estimates also suggest concurrent increases in the frequency of both extreme high and extreme low temperatures during 2002–2008, a period when we observe a plateauing of global mean temperature. Using daily extreme temperature observations, we find that the frequency of extreme high temperatures is greater in the daily minimum temperature time-series compared to the daily maximum temperature time-series. There is no such observable difference in the frequency of extreme low temperatures between the daily minimum and daily maximum.” Lalith Munasinghe, Tackseung Jun and David H. Rind, Climatic Change, DOI: 10.1007/s10584-011-0370-8.

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