Attribution of polar warming to human influence

Abstract

The polar regions have long been expected to warm strongly as a result of anthropogenic climate change, because of the positive feedbacks associated with melting ice and snow1,2. Several studies have noted a rise in Arctic temperatures over recent decades2,3,4, but have not formally attributed the changes to human influence, owing to sparse observations and large natural variability5,6. Both warming and cooling trends have been observed in Antarctica7, which the Intergovernmental Panel on Climate Change Fourth Assessment Report concludes is the only continent where anthropogenic temperature changes have not been detected so far, possibly as a result of insufficient observational coverage8. Here we use an up-to-date gridded data set of land surface temperatures9,10 and simulations from four coupled climate models to assess the causes of the observed polar temperature changes. We find that the observed changes in Arctic and Antarctic temperatures are not consistent with internal climate variability or natural climate drivers alone, and are directly attributable to human influence. Our results demonstrate that human activities have already caused significant warming in both polar regions, with likely impacts on polar biology, indigenous communities2, ice-sheet mass balance and global sea level11.

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Figure 1: Simulated and observed Arctic and Antarctic mean temperature anomalies.
Figure 2: Simulated and observed grid cell temperature trends.
Figure 3: Observed and simulated SAM-congruent and SAM-residual temperature trends over the period 1950–1999.
Figure 4: Regression coefficients of observed polar temperature anomalies against the simulated response to anthropogenic (x axis) and natural (y axis) forcing.

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Acknowledgements

We thank S. Solomon, G. Marshall and H. Melling for useful advice and discussion; M. Allen for his optimal detection and attribution code; and G. Jones for assistance with the provision of model output. This work was supported in part by the Climate Change Detection and Attribution Project, jointly funded by NOAA’s Office of Global Programs and the US Department of Energy. N.P.G. and A.Y.K. were also supported by NERC grant NE/E006787/1, and N.P.G. acknowledges support from the Leverhulme Trust. P.A.S. was supported by the Joint Defra and MoD Programme, (Defra) GA01101 (MoD) CBC/2B/0417 Annex C5.

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N.P.G. carried out most of the analysis and wrote the paper. D.A.S., P.A.S., T.N. and M.F.W. assisted with the provision of model data. A.Y.K. calculated SAM trends and regression patterns. G.C.H. proposed the study. P.D.J. provided advice on observations.

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Correspondence to Nathan P. Gillett.

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Gillett, N., Stone, D., Stott, P. et al. Attribution of polar warming to human influence. Nature Geosci 1, 750–754 (2008). https://doi.org/10.1038/ngeo338

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