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.