Spatial patterns of recent Antarctic surface temperature trends and the importance of natural variability: lessons from multiple reconstructions and the CMIP5 models
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The recent annually averaged warming of the Antarctic Peninsula, and of West Antarctica, stands in stark contrast to very small trends over East Antarctica. This asymmetry arises primarily from a highly significant warming of West Antarctica in austral spring and a cooling of East Antarctica in austral autumn. Here we examine whether this East–West asymmetry is a response to anthropogenic climate forcings or a manifestation of natural climate variability. We compare the observed Antarctic surface air temperature trends over two distinct time periods (1960–2005 and 1979–2005), and with those simulated by 40 models participating in Phase 5 of the Coupled Model Intercomparison Project (CMIP5). We find that the observed East–West asymmetry differs substantially between the two periods and, furthermore, that it is completely absent from the forced response seen in the CMIP5 multi-model mean, from which all natural variability is eliminated by the averaging. We also examine the relationship between the Southern Annular mode (SAM) and Antarctic temperature trends, in both models and reanalyses, and again conclude that there is little evidence of anthropogenic SAM-induced driving of the recent temperature trends. These results offer new, compelling evidence pointing to natural climate variability as a key contributor to the recent warming of West Antarctica and of the Peninsula.
KeywordsAntarctic climate change Climate variability Coupled climate models
This work is funded, in part, by a grant from the National Science Foundation (NSF) to Columbia University. KLS is also funded by a Natural Sciences and Engineering Research Council of Canada (NSERC) Postdoctoral Fellowship. We acknowledge the World Climate Research Programme Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups for producing and making available their model output. For CMIP the U.S. Department of Energy Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. The authors wish to express their gratitude to David Schneider for several eye-opening conversations and to Andrew Monaghan for providing his updated Antarctic temperature reconstruction. KLS would also like to thank Michael Previdi, Gabriel Chiodo and Abraham Solomon. CMIP5 data for this article was obtained online via the Earth System Grid portal, the CHAPMAN data was obtained at http://igloo.atmos.uiuc.edu/ANTARCTIC, the GISTEMP data was obtained at http://www.esrl.noaa.gov/psd/data/gridded/, the M10 data was made available to us by request from A. Monaghan (email@example.com), and the Steig data was obtained at http://faculty.washington.edu/steig/nature09data/data.
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