Very cold winter in eastern North America may be linked to warming of the Arctic

GallonDaily readers may have noticed that the recent very cold winter in eastern Canada has caused a number of climate change deniers to write letters to editors and elsewhere claiming that the winter is proof that climate change is not happening. A recent article by Jennifer A Francis of the Institute of Marine and Coastal Sciences, Rutgers University, and Stephen J Vavrus of the Center for Climatic Research, University of Wisconsin-Madison in the journal Environmental Research Letters provides evidence that the recent very cold winter in eastern Canada may in fact be a result of the impact of climate change in the Arctic.

The article presents evidence supporting a linkage between rapid Arctic warming and more frequent wavy jet-stream configurations that favour persistent weather patterns. Their results suggest that as the Arctic continues to warm faster than elsewhere in response to rising greenhouse-gas concentrations, the frequency of extreme weather events caused by persistent jet-stream patterns will increase.

The Arctic has warmed at approximately twice the rate of northern mid-latitudes since the 1990s owing to a variety of positive feedbacks that amplify greenhouse-gas-induced global warming. This disproportionate temperature rise in the Arctic is expected to influence the large-scale circulation, perhaps with far-reaching effects. The North/South temperature gradient is an important driver of the polar jet stream, thus as rapid Arctic warming continues, one anticipated effect is a slowing of upper-level zonal winds. The authors’ analysis supports the hypothesis that these weakened winds will cause the path of the jet stream to become more meandering, leading to slower Eastward progression of ridges and troughs, which increases the likelihood of persistent weather patterns and, consequently, extreme events.

Widespread Arctic change continues to intensify, as evidenced by continued loss of Arctic sea ice, decreasing mass of Greenland’s ice sheet, rapid decline of snow cover on Northern hemisphere continents during early summer, and the continued rapid warming of the Arctic relative to mid-latitudes. These events are driven by a phenomenon known as Arctic amplification – the enhanced sensitivity of Arctic temperature change relative to mid-latitude regions, but they also amplify it: melting ice and snow expose the dark surfaces beneath, which reduces the surface albedo (heat energy reflectivity) , further enhances the absorption of insolation (the total solar energy received on a given surface in a given time), and exacerbates melting. Expanding ice-free areas in the Arctic Ocean also lead to additional evaporation that augments warming and Arctic precipitation.

Put in the most basic language, the paper, if its analysis is correct, indicates that, when it comes to extreme weather events in eastern North America, you ain’t seen anything yet! For corporate, government, and even household planners the resulting advice might be to get ready for even greater extremes, both higher and lower, of temperature, wind, and precipitation. Far from being evidence that climate change does not exist, the cold winter in eastern North America may in fact be evidence that climate change is already happening.

The research paper Evidence for a wavier jet stream in response to rapid Arctic warming is available at http://iopscience.iop.org/1748-9326/10/1/014005/article?fromSearchPage=true

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