AGW Observer

Observations of anthropogenic global warming

New research from last week 36/2011

Posted by Ari Jokimäki on September 12, 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.

Published last week:

Studying individual glaciers

Those interested in glaciers, be sure to check out the index of glacier posts in Mauri Pelto’s blog “From a Glaciers Perspective”.

Causes of changes in Arctic multiyear sea ice

Recent changes of arctic multiyear sea-ice coverage and the likely causes – Polyakov et al. (2011) No abstract. Igor V. Polyakov, Ronald Kwok, and John E. Walsh, Bulletin of the American Meteorological Society 2011, doi: 10.1175/BAMS-D-11-00070.1. [Full text]

Great Lakes have been losing ice cover

Temporal and spatial variability of Great Lakes ice cover, 1973–2010 – Wang et al. (2011) “In this study, temporal and spatial variability of ice cover in the Great Lakes are investigated using historical satellite measurements from 1973 to 2010. The seasonal cycle of ice cover was constructed for all the lakes including Lake St. Clair. A unique feature found in the seasonal cycle is that the standard deviations (i.e., variability) of ice cover are larger than the climatological means for each lake. This indicates that Great Lakes ice cover experiences large variability in response to predominant natural climate forcing and has poor predictability. Spectral analysis shows that lake ice has both quasi-decadal and interannual periodicities of ~8 years and ~4 years. There was a significant downward trend in ice coverage from 1973 to the present for all the lakes, with Lake Ontario having the largest, and Lakes Erie and St. Clair having the smallest. The translated total loss in lake ice over the entire 38-year record varies from 37% in Lake St. Clair (least) to 88% in Lake Ontario (most). The total loss for overall Great Lakes ice coverage is 71%, while Lake Superior places second with a 79% loss. An EOF (empirical orthogonal function) analysis indicates that a major response of ice cover to atmospheric forcing is in phase in all six lakes, accounting for 80.8% of the total variance. The second mode shows an out-of-phase spatial variability between the upper lakes and lower lakes, accounting for 10.7% of the total variance. The regression of the first EOF-mode time series to sea level pressure, surface air temperature, and surface wind shows that lake ice mainly responds to the combined AO (Arctic Oscillation) and ENSO (El Nino and Southern Oscillation) patterns.” Jia Wang, Xuezhi Bai, Haohuo Hu, Anne Clites, Marie Colton, and Brent Lofgren, Journal of Climate 2011, doi: 10.1175/2011JCLI4066.1.

Sea ice loss increases Arctic coastal erosion

Sea ice loss enhances wave action at the Arctic coast – Overeem et al. (2011) “Erosion rates of permafrost coasts along the Beaufort Sea accelerated over the past 50 years synchronously with Arctic-wide declines in sea ice extent, suggesting a causal relationship between the two. A fetch-limited wave model driven by sea ice position and local wind data from northern Alaska indicates that the exposure of permafrost bluffs to seawater increased by a factor of 2.5 during 1979–2009. The duration of the open water season expanded from ∼45 days to ∼95 days. Open water expanded more rapidly toward the fall (∼0.92 day yr−1), when sea surface temperatures are cooler, than into the mid-summer (∼0.71 days yr−1).Time-lapse imagery demonstrates the relatively efficient erosive action of a single storm in August. Sea surface temperatures have already decreased significantly by fall, reducing the potential impact of thermal erosion due to fall season storm waves.” Overeem, I., R. S. Anderson, C. W. Wobus, G. D. Clow, F. E. Urban, and N. Matell (2011), Geophys. Res. Lett., 38, L17503, doi:10.1029/2011GL048681.

How well models reproduce 20th century temperature?

A balance between radiative forcing and climate feedback in the modeled 20th century temperature response – Crook & Forster (2011) “In this paper, we breakdown the temperature response of coupled ocean-atmosphere climate models into components due to radiative forcing, climate feedback, and heat storage and transport to understand how well climate models reproduce the observed 20th century temperature record. Despite large differences between models’ feedback strength, they generally reproduce the temperature response well but for different reasons in each model. We show that the differences in forcing and heat storage and transport give rise to a considerable part of the intermodel variability in global, Arctic, and tropical mean temperature responses over the 20th century. Projected future warming trends are much more dependent on a model’s feedback strength, suggesting that constraining future climate change by weighting these models on the basis of their 20th century reproductive skill is not possible. We find that tropical 20th century warming is too large and Arctic amplification is unrealistically low in the Geophysical Fluid Dynamics Laboratory CM2.1, Meteorological Research Institute CGCM232a, and MIROC3.2(hires) models because of unrealistic forcing distributions. The Arctic amplification in both National Center for Atmospheric Research models is unrealistically high because of high feedback contributions in the Arctic compared to the tropics. Few models reproduce the strong observed warming trend from 1918 to 1940. The simulated trend is too low, particularly in the tropics, even allowing for internal variability, suggesting there is too little positive forcing or too much negative forcing in the models at this time. Over the whole of the 20th century, the feedback strength is likely to be underestimated by the multimodel mean.” Crook, J. A., and P. M. Forster (2011), J. Geophys. Res., 116, D17108, doi:10.1029/2011JD015924.

Warm nights have become more common globally

Detectable regional changes in the number of warm nights – Morak et al. (2011) “In this study we analyse gridded observed and multi-model simulated trends in the annual number of warm nights during the second half of the 20th century. We show that there is evidence that external forcing has significantly increased the number of warm nights, both globally and over many regions. We define thirteen regions with a high density of observational data over two datasets, for which we compare observed and simulated trends from 20th century simulations. The main analysis period is 1951–1999, with a sub-period of 1970–1999. In order to investigate if observed trends changed past 1999, we also analysed periods of 1955–2003 and 1974–2003. Both observed and ensemble mean model data from all models analysed show a positive trend for the regional mean number of warm nights in all regions within this 49 year period (1951–1999). The trends tend to become more pronounced over the sub-period 1970–1999 and even more so up to 2003. We apply a fingerprint analysis to assess if trends are detectable relative to internal climate variability. We find that changes in the global scale analysis, and in 9 out of 13 regions, are detectable at the 5% significance level. A large part of the observed global-scale trend in TN90 results from the trend in mean temperature, which has been attributed largely to anthropogenic greenhouse gas increase. This suggests that the detected global-scale trends in the number of warm nights are at least partly anthropogenic.” Morak, S., G. C. Hegerl, and J. Kenyon (2011), Geophys. Res. Lett., 38, L17703, doi:10.1029/2011GL048531.

Ship wakes have small cooling effect on climate

Effects of ship wakes on ocean brightness and radiative forcing over ocean – Gatebe et al. (2011) “Changes in surface albedo represent one of the main forcing agents that can counteract, to some extent, the positive forcing from increasing greenhouse gas concentrations. Here, we report on enhanced ocean reflectance from ship wakes over the Pacific Ocean near the California coast, where we determined, based on airborne radiation measurements that ship wakes can increase reflected sunlight by more than 100%. We assessed the importance of this increase to climate forcing, where we estimated the global radiative forcing of ship wakes to be −(0.14 ± 50%) mWm−2 assuming a global distribution of 32331 ships of size ≥100000 gross tonnage. The forcing is smaller than the forcing of aircraft contrails (−0.007 to +0.02 Wm−2), but considering that the global shipping fleet has rapidly grown in the last five decades and this trend is likely to continue because of the need of more inter-continental transportation as a result of economic globalization, we argue that the radiative forcing of wakes is expected to be increasingly important especially in harbors and coastal regions.” Gatebe, C. K., E. Wilcox, R. Poudyal, and J. Wang (2011), Geophys. Res. Lett., 38, L17702, doi:10.1029/2011GL048819. [Full text]

Indian Ocean leaks warmth to Atlantic Ocean

What caused the significant increase in Atlantic Ocean heat content since the mid-20th century? – Lee et al. (2011) “As the upper layer of the world ocean warms gradually during the 20th century, the inter-ocean heat transport from the Indian to Atlantic basin should be enhanced, and the Atlantic Ocean should therefore gain extra heat due to the increased upper ocean temperature of the inflow via the Agulhas leakage. Consistent with this hypothesis, instrumental records indicate that the Atlantic Ocean has warmed substantially more than any other ocean basin since the mid-20th century. A surface-forced global ocean-ice coupled model is used to test this hypothesis and to find that the observed warming trend of the Atlantic Ocean since the 1950s is largely due to an increase in the inter-ocean heat transport from the Indian Ocean. Further analysis reveals that the increased inter-ocean heat transport is not only caused by the increased upper ocean temperature of the inflow but also, and more strongly, by the increased Agulhas Current leakage, which is augmented by the strengthening of the wind stress curl over the South Atlantic and Indian subtropical gyre.” Lee, S.-K., W. Park, E. van Sebille, M. O. Baringer, C. Wang, D. B. Enfield, S. G. Yeager, and B. P. Kirtman (2011), Geophys. Res. Lett., 38, L17607, doi:10.1029/2011GL048856. [Full text]

Temperature–mortality relationship in Korea

Vulnerability to temperature-related mortality in Seoul, Korea – Son et al. (2011) “Studies indicate that the mortality effects of temperature may vary by population and region, although little is known about the vulnerability of subgroups to these risks in Korea. This study examined the relationship between temperature and cause-specific mortality for Seoul, Korea, for the period 2000–7, including whether some subgroups are particularly vulnerable with respect to sex, age, education and place of death. The authors applied time-series models allowing nonlinear relationships for heat- and cold-related mortality, and generated exposure–response curves. Both high and low ambient temperatures were associated with increased risk for daily mortality. Mortality risk was 10.2% (95% confidence interval 7.43, 13.0%) higher at the 90th percentile of daily mean temperatures (25 °C) compared to the 50th percentile (15 °C). Mortality risk was 12.2% (3.69, 21.3%) comparing the 10th (−1 °C) and 50th percentiles of temperature. Cardiovascular deaths showed a higher risk to cold, whereas respiratory deaths showed a higher risk to heat effect, although the differences were not statistically significant. Susceptible populations were identified such as females, the elderly, those with no education, and deaths occurring outside of a hospital for heat- and cold-related total mortality. Our findings provide supportive evidence of a temperature–mortality relationship in Korea and indicate that some subpopulations are particularly vulnerable” Ji-Young Son et al 2011 Environ. Res. Lett. 6 034027 doi: 10.1088/1748-9326/6/3/034027. [Full text]

New Dessler paper shows Spencer cherry-picking datasets

Cloud variations and the Earth’s energy budget – Dessler (2011) “The question of whether clouds are the cause of surface temperature changes, rather than acting as a feedback in response to those temperature changes, is explored using data obtained between 2000 and 2010. An energy budget calculation shows that the energy trapped by clouds accounts for little of the observed climate variations. And observations of the lagged response of top-of-atmosphere (TOA) energy fluxes to surface temperature variations are not evidence that clouds are causing climate change.” Dessler, A. E. (2011), Geophys. Res. Lett., doi:10.1029/2011GL049236.

Late nesting ducks experience most severe population declines with global warming

Population Vulnerability to Climate Change Linked to Timing of Breeding in Boreal Ducks – Drever et al. (2011) “Identifying and understanding why traits make species vulnerable to changing climatic conditions remain central problems in evolutionary and applied ecology. We used spring snow cover duration as a proxy for phenological timing of wetland ecosystems, and examined how snow cover duration during spring and during the entire snow season affected population dynamics of duck species breeding in the western boreal forest of North America, 1973-2007. We predicted that population-level responses would differ among duck species, such that late-nesting species with reduced flexibility in their timing of breeding, i.e. scaup (Aythya spp.) and scoter (Melanitta spp.), would be more strongly affected by changing snow cover conditions relative to species better able to adjust timing of breeding to seasonal phenology, i.e. mallard (Anas platyrhynchos) and American wigeon (Anas americana). Population growth rates of scaup and scoter were positively linked to spring snow cover duration; after accounting for effects of density dependence, larger breeding season populations resulted after springs with longer snow cover duration than after springs with shorter snow cover duration. In contrast, population growth rates of mallard and wigeon were either negatively or only weakly associated with snow cover duration. Duck population models were then incorporated with snow cover duration derived from climate model simulations under the A2 emission scenario, and these predictions suggested that late-nesting duck species will experience the most severe population declines. Results are consistent with a hypothesis that the gradual climatic warming observed in the western boreal forest of North America has contributed to and may continue to exacerbate population declines of scaup and scoter.” Mark C. Drever, Robert G. Clark, Chris Derksen, Stuart M. Slattery, Peter Toose, Thomas D. Nudds, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02541.x.

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