AGW Observer

Observations of anthropogenic global warming

New research from last week 31/2011

Posted by Ari Jokimäki on August 8, 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:

Clouds are too reflective in many models in tropical convection regions

Reproducibility by climate models of cloud radiative forcing associated with tropical convection – Ichikawa et al. (2011) “In this study, cloud radiative forcing (CRF) associated with convective activity over tropical oceans is analyzed for monthly mean data of the twentieth-century simulations of 18 climate models participating in the phase 3 of the Coupled Model Intercomparison Project (CMIP3) in comparison with observational and reanalysis data. The analysis is focused on the warm oceanic regions with sea surface temperatures (SSTs) above 27°C to exclude the regions with cold SSTs typically covered by low stratus clouds. CRF is evaluated for different regimes sorted by pressure-coordinated vertical motion at 500 hPa (ω 500) as an index of large-scale circulation. The warm oceanic regions cover the regime of vertical motion ranging from strong ascent to weak descent. The most notable feature found in this study is a systematic underestimation by most models of the ratio of longwave cloud radiative forcing (LWCRF) to shortwave cloud radiative forcing (SWCRF) over the weak vertical motion regime defined as −10 < ω 500 < 20 hPa day−1. The underestimation of the ratio corresponds to the underestimation of LWCRF and the overestimation of SWCRF. Clouds in models seem to be lower in amount of high clouds but more reflective than those in the observation in this regime. In the weak vertical motion regime, the lower free troposphere is dry. In the large-scale environment condition, the reproducibility of LWCRF is high in models adopting the scheme where the relative humidity-based suppression for deep convection occurrence is implemented. Models adopting Zhang and McFarlane scheme show good performance without such a suppression mechanism." Hiroki Ichikawa, Hirohiko Masunaga, Yoko Tsushima, and Hiroshi Kanzawa, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00114.1.

Strong and highly variable N2O emission sources in tropics

Tropospheric distribution and variability of N2O: Evidence for strong tropical emissions – Kort et al. (2011) “Measurements of atmospheric N2O spanning altitudes from the surface to 14 km, and latitudes from 67°S to 85°N, show high concentrations in the tropics and subtropics, with strong maxima in the middle and upper troposphere. The pattern varies significantly over time scales of a few weeks. Global simulations do not accurately capture observed distributions with latitude, altitude, or time. Inversion results indicate strong, episodic inputs of nitrous oxide from tropical regions (as large as 1 Tg N-N2O over 9 weeks) are necessary to produce observed vertical and latitudinal distributions. These findings highlight strong tropical sources of N2O with high temporal variability, and the necessity of using full vertical profile observations in deriving emissions from atmospheric measurements.” Kort, E. A., P. K. Patra, K. Ishijima, B. C. Daube, R. Jiménez, J. Elkins, D. Hurst, F. L. Moore, C. Sweeney, and S. C. Wofsy (2011), Geophys. Res. Lett., 38, L15806, doi:10.1029/2011GL047612. [Full text]

Oysters might be able to adapt to ocean acidification

Adult exposure influences offspring response to ocean acidification in oysters – Parker et al. (2011) “It is essential to predict the impact of elevated Pco2 on marine organisms and habitats in order to anticipate the severity and consequences of future ocean chemistry change. Despite the importance of carry-over effects in the evolutionary history of marine organisms, few studies have considered links between life-history stages when determining how marine organisms will respond to elevated Pco2, and none have considered the link between adults and their offspring. Here we exposed adults of wild and selectively bred Sydney rock oysters, Saccostrea glomerata to elevated Pco2 during reproductive conditioning and measured the development, growth and survival response of their larvae. We found that elevated Pco2 had a negative impact on larvae of S. glomerata causing a reduction in growth, rate of development and survival. Exposing adults to elevated Pco2 during reproductive conditioning, however, had positive carry-over effects on larvae. Larvae spawned from adults exposed to elevated Pco2 were larger, developed faster but displayed similar survival compared to larvae spawned from adults exposed to ambient Pco2. Further, selectively bred larvae of S. glomerata were more resilient to elevated Pco2 than wild larvae. Measurement of the standard metabolic rate (SMR) of adult S. glomerata showed that at ambient Pco2, SMR is increased in selectively bred compared to wild oysters and is further increased during exposure to elevated Pco2. This study suggests that sensitive marine organisms may have the capacity to acclimate or adapt to elevated Pco2 over the next century and a change in energy turnover indicated by SMR may be a key process involved.” Laura M. Parker, Pauline M. Ross, Wayne A. O’Connor, Larissa Borysko, David A. Raftos, Hans-Otto Pörtner, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02520.x.

Aerobic permafrost carbon release might have stronger effect on climate than anaerobic

The Rate of Permafrost Carbon Release Under Aerobic and Anaerobic Conditions and its Potential Effects on Climate – Lee et al. (2011) “Recent observations suggest that permafrost thaw may create two completely different soil environments: aerobic in relatively well-drained uplands and anaerobic in poorly-drained wetlands. The soil oxygen availability will dictate the rate of permafrost carbon release as carbon dioxide (CO2) and as methane (CH4), and the overall effects of these emitted greenhouse gases on climate. The objective of this study was to quantify CO2 and CH4 release over a 500-day period from permafrost soil under aerobic and anaerobic conditions in the laboratory and to compare the potential effects of these emissions on future climate by estimating their relative climate forcing. We used permafrost soils collected from Alaska and Siberia with varying organic matter characteristics and simultaneously incubated them under aerobic and anaerobic conditions to determine rates of CO2 and CH4 production. Over 500 days of soil incubation at 15°C, we observed that carbon released under aerobic conditions was 3.9 to 10.0 times greater than anaerobic conditions. When scaled by greenhouse warming potential to account for differences between CO2 and CH4, relative climate forcing ranged 1.5-7.1. Carbon release in organic soils was nearly 20 times greater than mineral soils on a per gram soil basis, but when compared on a per gram carbon basis deep permafrost mineral soils showed a similar carbon release rates as organic soils for some soil types. This suggests that permafrost carbon may be very labile but that there are significant differences across soil types depending on the processes that controlled initial permafrost carbon accumulation within a particular landscape. Overall, our study showed that, independent of soil type, permafrost carbon in a relatively aerobic upland ecosystems may have a greater effect on climate as compared to a similar amount of permafrost carbon thawing in an anaerobic environment, despite the release of CH4 that occurs in anaerobic conditions.” Hanna Lee, Edward A. G. Schuur, Kanika S. Inglett, Martin Lavoie, Jeffrey P. Chanton, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02519.x.

New Willie Soon paper highlights solar effect to China temperatures

Variation in surface air temperature of China during the 20th century – Soon et al. (2011) “The 20th century surface air temperature (SAT) records of China from various sources are analyzed using data which include the recently-released Twentieth Century Reanalysis Project dataset. Two key features of the Chinese records are confirmed: (1) significant 1920 s and 1940 s warming in the temperature records, and (2) evidence for a persistent multi-decadal modulation of the Chinese surface temperature records in covariations with both incoming solar radiation at the top of the atmosphere as well as the modulated solar radiation reaching ground surface. New evidence is presented for this Sun-climate link for the instrumental record from 1880 to 2002. Additionally, two non-local physical aspects of solar radiation-induced modulation of the Chinese SAT record are documented and discussed. Teleconnections that provide a persistent and systematic modulation of the temperature response of the Tibetan Plateau and/or the tropospheric air column above the Eurasian continent (e.g., 30°N-70°N; 0°-120°E) are described. These teleconnections may originate from the solar irradiance-Arctic-North Atlantic Overturning Circulation mechanism proposed by Soon (2009). Also considered is the modulation of large-scale land-sea thermal contrasts both in terms of meridional and zonal gradients between the subtropical western Pacific and mid-latitude North Pacific and the continental landmass of China. The Circum-global Teleconnection (CGT) pattern of summer circulation of Ding and Wang (2005) provides a physical framework for study of the Sun-climate connection over East Asia. Our results highlight the importance of solar radiation reaching the ground and the concomitant importance of changes in atmospheric transparency or cloudiness or both in motivating a true physical explanation of any Sun-climate connection. We conclude that ground surface solar radiation is an important modulating factor for Chinese SAT changes on multidecadal to centennial timescales. Therefore, a comprehensive view of local and remote factors of climate change in China must take account of this as well as other natural and anthropogenic forcings.” Willie Soon, Koushik Dutta, David R. Legates, Victor Velasco and WeiJia Zhang, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.07.007.

New analysis of tropical upper troposphere warming

On the warming in the tropical upper troposphere: Models versus observations – Fu et al. (2011) “IPCC (Intergovernmental Panel on Climate Change) AR4 (Fourth Assessment Report) GCMs (General Circulation Models) predict a tropical tropospheric warming that increases with height, reaches its maximum at ∼200 hPa, and decreases to zero near the tropical tropopause. This study examines the GCM-predicted maximum warming in the tropical upper troposphere using satellite MSU (microwave sounding unit)-derived deep-layer temperatures in the tropical upper- and lower-middle troposphere for 1979–2010. While satellite MSU/AMSU observations generally support GCM results with tropical deep-layer tropospheric warming faster than surface, it is evident that the AR4 GCMs exaggerate the increase in static stability between tropical middle and upper troposphere during the last three decades.” Fu, Q., S. Manabe, and C. M. Johanson (2011), Geophys. Res. Lett., 38, L15704, doi:10.1029/2011GL048101.

Analysis of tropical belt widening

A multi-diagnostic intercomparison of tropical width time series using reanalyses and satellite observations – Davis & Rosenlof (2011) “Poleward migration of the latitudinal edge of the tropics of ~0.25 – 3° decade−1 has been reported in several recent studies based on satellite and radiosonde data, and reanalysis output covering the past ~30 years. The goal of this paper is to identify the extent to which this large range of trends can be explained by the use of different data sources, time periods, and edge definitions, as well as how the widening varies as a function of hemisphere and season. Towards this end, we apply a suite of tropical edge latitude diagnostics based on tropopause height, winds, precipitation/evaporation, and outgoing longwave radiation (OLR) to several reanalyses and satellite data sets. These diagnostics include both previously used definitions and new definitions designed for more robust detection. The wide range of widening trends is shown to be primarily due to the use of different data sets and edge definitions, and only secondarily due to varying start/end dates. We also show that the large trends (> ~ 1° decade−1) previously reported in tropopause and OLR diagnostics are due to the use of subjective definitions based on absolute thresholds. Statistically significant Hadley cell expansion based on the mean meridional streamfunction of 1.0 – 1.5° decade−1 is found in three of four reanalyses that cover the full time period (1979–2009), whereas other diagnostics yield trends of −0.5 – 0.8° decade−1 that are mostly insignificant. There are indications of hemispheric and seasonal differences in the trends, but the differences are not statistically significant.” Sean M. Davis, Karen H. Rosenlof, Journal of Climate 2011, doi: 10.1175/JCLI-D-11-00127.1.

Stratosphere ozone recovery probably warms troposphere

Tropospheric temperature response to stratospheric ozone recovery in the 21st century – Hu et al. (2011) “Recent simulations predicted that the stratospheric ozone layer will likely return to pre-1980 levels in the middle of the 21st century, as a result of the decline of ozone depleting substances under the Montreal Protocol. Since the ozone layer is an important component in determining stratospheric and tropospheric-surface energy balance, the recovery of stratospheric ozone may have significant impact on tropospheric-surface climate. Here, using multi-model results from both the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC-AR4) models and coupled chemistry-climate models, we show that as ozone recovery is considered, the troposphere is warmed more than that without considering ozone recovery, suggesting an enhancement of tropospheric warming due to ozone recovery. It is found that the enhanced tropospheric warming is mostly significant in the upper troposphere, with a global and annual mean magnitude of ~0.41 K for 2001–2050. We also find that relatively large enhanced warming occurs in the extratropics and polar regions in summer and autumn in both hemispheres, while the enhanced warming is stronger in the Northern Hemisphere than in the Southern Hemisphere. Enhanced warming is also found at the surface. The global and annual mean enhancement of surface warming is about 0.16 K for 2001–2050, with maximum enhancement in the winter Arctic.” Hu, Y., Xia, Y., and Fu, Q., Atmos. Chem. Phys., 11, 7687-7699, doi:10.5194/acp-11-7687-2011, 2011. [Full text]

Global temperature reconstruction from glacier length fluctuations shows 20th century warming

Global and hemispheric temperature reconstruction from glacier length fluctuations – Leclercq & Oerlemans (2011) “Temperature reconstructions for recent centuries provide a historical context for the warming over the twentieth century. We reconstruct annual averaged surface temperatures of the past 400 years on hemispherical and global scale from glacier length fluctuations. We use the glacier length records of 308 glaciers. The reconstruction is a temperature proxy with decadal resolution that is completely independent of other temperature records. Temperatures are derived from glacier length changes using a linear response equation and an analytical glacier model that is calibrated on numerical model results. The global and hemispherical temperatures reconstructed from glacier length fluctuations are in good agreement with the instrumental record of the last century. Furthermore our results agree with existing multi-proxy reconstructions of temperature in the pre-instrumental period. The temperature record obtained from glacier fluctuations confirms the pronounced warming of the twentieth century, giving a global cumulative warming of 0.94 ± 0.31 K over the period 1830–2000 and a cumulative warming of 0.84 ± 0.35 K over the period 1600–2000.” Paul Willem Leclercq and Johannes Oerlemans, Climate Dynamics, DOI: 10.1007/s00382-011-1145-7. [Full text]

Using marine mammals to measure high latitude Atlantic temperatures

Temperature signature of high latitude Atlantic boundary currents revealed by marine mammal-borne sensor and Argo data – Grist et al. (2011) “Results from the development and analysis of a novel temperature dataset for the high latitude North-West Atlantic are presented. The new 1° gridded dataset (“ATLAS”) has been produced from about 13,000 Argo and 48,000 marine mammal (hooded seal, harp seal, grey seal and beluga) profiles spanning 2004–8. These data sources are highly complementary as marine mammals greatly enhance shelf region coverage where Argo floats are absent. ATLAS reveals distinctive boundary current related temperature minima in the Labrador Sea (−1.1°C) and at the east Greenland coast (1.8°C), largely absent in the widely-used Levitus’09 and EN3v2a datasets. The ATLAS 0–500 m average temperature is lower than Levitus’09 and EN3v2a by up to 3°C locally. Differences are strongest from 0–300 m and persist at reduced amplitude from 300–500 m. Our results clearly reveal the value of marine mammal-borne sensors for a reliable description of the North-West Atlantic at a time of rapid change.” Grist, J. P., S. A. Josey, L. Boehme, M. P. Meredith, F. J. M. Davidson, G. B. Stenson, and M. O. Hammill (2011), Geophys. Res. Lett., 38, L15601, doi:10.1029/2011GL048204.

Southern China extreme cold winter events getting rare

Extreme cold winter events in southern China during AD 1650–2000 – Zheng et al. (2011) “We defined extreme cold winter events as those with occurrence probabilities lower than the 10th percentile of the probability density function, based on observed winter temperatures in southern China since 1951. Subsequently, we constructed impact severity levels using documentary evidence for those events during 1951–2000, considering three indexes for the freezing of rivers/lakes, widespread snow/ice storms, and cold damage to subtropical/tropical crops. Using these criteria we identified 50 extreme cold winters for the period AD 1650–1949 based on ∼4000 pieces of comparable information extracted from local gazettes in southern China, after verification using data from three weather stations with long records. It was found that the frequencies of the extreme cold winter events since 1650 varied over time. The most frequent occurrences were found during AD 1650–1699 and in the first and second halves of the 19th century, with frequencies twice as high as in the second half of the 20th century. In contrast, the frequencies of extreme winters during the 18th century were close to that in the second half of the 20th century. High frequencies of extreme cold winters in AD 1650–1720 and AD 1795–1835 occurred during the sunspot Maunder and Dalton Minima. The intensities of some historical cold events, such as those during 1653–1654, 1670, 1690, 1861, 1892 and 1929, exceeded those of the coldest winter events since 1951.” Jingyun Zheng, Lingling Ding, Zhixin Hao, Quansheng Ge, Boreas, DOI: 10.1111/j.1502-3885.2011.00225.x.

Elevated CO2 has negative effect to wheat grain protein content

Yield vs. Quality trade-offs for wheat in response to carbon dioxide and ozone – Pleijel & Uddling (2011) “Although it is established that there exist potential trade-offs between grain yield and grain quality in wheat exposed to elevated carbon dioxide (CO2) and ozone (O3), their underlying causes remain poorly explored. To investigate the processes affecting grain quality under altered CO2 and O3, we analysed 57 experiments with CO2 or O3 exposure in different exposure systems. The study covered 24 cultivars studied in 112 experimental treatments from 11 countries. A significant growth dilution effect on grain protein was found: a change in grain yield of 10% by O3 was associated with a change in grain protein yield of 8.1% (R2 = 0.96), whereas a change in yield effect of 10% by CO2 was linked to a change in grain protein yield effect of 7.5% (R2 = 0.74). Superimposed on this effect, elevated CO2, but not O3, had a significant negative effect on grain protein yield also in the absence of effects on grain yield, indicating that there exists a process by which CO2 restricts grain protein accumulation, which is absent for O3. Grain mass, another quality trait, was more strongly affected by O3 than grain number, whereas the opposite was true for CO2. Harvest index was strongly and negatively influenced by O3, but was unaffected by CO2. We conclude that yield vs. protein trade-offs for wheat in response to CO2 and O3 are constrained by close relationships between effects on grain biomass and less than proportional effects on grain protein. An important and novel finding was that elevated CO2 has a direct negative effect on grain protein accumulation independent of the yield effect, supporting recent evidence of CO2-induced impairment of nitrate uptake/assimilation. Finally, our results demonstrated that processes underlying responses of grain yield vs. quality trade-offs are very different in wheat exposed to elevated O3 compared with elevated CO2.” Håkan Pleijel, Johan Uddling, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.2489.x.

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