Published this week in the NIPCC Report:
Global Warming Fosters High Latitude Cooling?
In a study published in Environmental Research Letters, Cohen et al. (2012) note that over the last four decades Arctic temperatures have warmed at nearly double the global rate, citing Solomon et al. (2007) and Screen and Simmonds (2010); and they state that "coupled climate models attribute much of this warming to rapid increases in greenhouse gases and project the strongest warming across the extratropical Northern Hemisphere during boreal winter due to 'winter (or Arctic) amplification'," citing Holland and Bitz (2003), Hansen and Nazarenko (2004), Alexeev et al. (2005) and Langen and Alexeev (2007). However, they say that "recent trends in observed Northern Hemisphere winter surface temperatures diverge from these projections," noting that "while the planet has steadily warmed, Northern Hemisphere winters have recently grown more extreme across the major industrialized centers," and reporting that "record cold snaps and heavy snowfall events across the United States, Europe and East Asia garnered much public attention during the winters of 2009/10 and 2010/11 (Blunden et al., 2011; Cohen et al., 2010)," with the latter set of researchers suggesting that "the occurrence of more severe Northern Hemisphere winter weather is a two-decade-long trend starting around 1988."
So what's going on here?
Cohen et al. say that "whether the recent colder winters are a consequence of internal variability or a response to changes in boundary forcings resulting from climate change remains an open question." But like most scientists who love to resolve dilemmas, they go on to propose their answer to the puzzle, suggesting that "summer and autumn warming trends are concurrent with increases in high-latitude moisture and an increase in Eurasian snow cover, which dynamically induces large-scale wintertime cooling."
But, again, who knows? The only thing that is certain, as Cohen et al. describe it, is that "traditional radiative greenhouse gas theory and coupled climate models forced by increasing greenhouse gases alone cannot account for this seasonal asymmetry." And so we have yet another reason why so many scientists are so skeptical about the ability of even the most sophisticated of today's climate models to adequately portray reality.
Cohen, J., Foster, J., Barlow, M., Saito, K. and Jones, J. 2010. Winter 2009/10: a case study of an extreme Arctic Oscillation event. Geophysical Research Letters 37: 10.1029/2010GL044256.
Alexeev, V.A., Langen, P.L. and Bates, J.R. 2005. Polar amplification of surface warming on an aquaplanet in 'ghost forcing' experiments without sea ice feedbacks. Climate Dynamics 24: 655-666.
Blunden, J., Arndt, D.S. and Baringer, M.O. 2011. State of the climate in 2010. Bulletin of the American Meteorological Society 92: S1-S236.
Cohen, J.L., Furtado, J.C., Barlow, M.A., Alexeev, V.A. and Cherry, J.E. 2012. Arctic warming, increasing snow cover and widespread boreal winter cooling. Environmental Research Letters 7: 10.1088/1748-9326/7/1/014007.
Hansen, J. and Nazarenko, L. 2004. Soot climate forcing via snow and ice albedos. Proceedings of the National Academy of Sciences USA 101: 3488-3499.
Holland, M.M. and Bitz, C.M. 2003. Polar amplification of climate change in coupled models. Climate Dynamics 21: 221-232.
Langen, P.L. and Alexeev, V.A. 2007. Polar amplification as a preferred response in an aquaplanet GCM. Climate Dynamics 29: 305-317.
Screen, J.A. and Simmonds, I. 2010. The central role of diminishing sea ice in recent Arctic temperature amplification. Nature 464: 1334-1337.
Solomon, S. et al. (Eds.). 2007. Climate Change 2007: The Physical Science Basis. Cambridge University Press, Cambridge, United Kingdom.