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A threat of irreversible damage should prompt action to mitigate climate change, according to the United Nations Framework Convention on Climate Change, which serves as a basis for international climate policy. CO2-induced climate change is known to be largely irreversible on timescales of many centuries1, as simulated global mean temperature remains approximately constant for such periods following a complete cessation of carbon dioxide emissions while thermosteric sea level continues to rise1, 2, 3, 4, 5, 6. Here we use simulations with the Canadian Earth System Model to show that ongoing regional changes in temperature and precipitation are significant, following a complete cessation of carbon dioxide emissions in 2100, despite almost constant global mean temperatures. Moreover, our projections show warming at intermediate depths in the Southern Ocean that is many times larger by the year 3000 than that realized in 2100. We suggest that a warming of the intermediate-depth ocean around Antarctica at the scale simulated for the year 3000 could lead to the collapse of the West Antarctic Ice Sheet, which would be associated with a rise in sea level of several metres2, 7, 8.
Canadian Centre for Climate Modelling and Analysis, Environment Canada, University of Victoria, PO 1700, STN CSC, Victoria, British Columbia, V8W 3V6, Canada
Nathan P. Gillett,
Vivek K. Arora,
Kirsten Zickfeld &
William J. Merryfield
Department of Geography, University of Calgary, 2500 University Drive N.W.Calgary, Alberta T2N 1N4, Canada
Shawn J. Marshall
N.P.G. designed the experiment, analysed model output, and wrote most of the paper. V.K.A. carried out the CanESM1 simulations, and wrote part of the Methods section. K.Z. contributed to the experimental design and analysis. S.J.M. contributed text and expertise on ice sheet implications. W.J.M. analysed ocean model output and contributed expertise on ocean changes.
Competing financial interests
The authors declare no competing financial interests.