Earth has warmed, and the Arctic has warmed at twice the rate. Ironically, says ScienceNow,
winters in the Northern Hemisphere have grown colder and more extreme in southern Canada, the eastern United States, and much of northern Eurasia, with England’s record-setting cold spell in December 2010 as a case in point.
Now Judah Cohen, et al, may have explained why in a report in Environmental Research Letters:
Siberian airport trapped in snow. Picture credit
First, the strong warming in the Arctic in recent decades, among other factors, has triggered widespread melting of sea ice. More open water in the Arctic Ocean has led to more evaporation, which moisturizes the overlying atmosphere, the researchers say. Previous studies have linked warmer-than-average summer months to increased cloudiness over the ocean during the following autumn. That, in turn, triggers increased snow coverage in Siberia as winter approaches. As it turns out, the researchers found, snow cover in October has the largest effect on climate in subsequent months.
That’s because widespread autumn snow cover in Siberia strengthens a semipermanent high-pressure system called, appropriately enough, the Siberian high, which reinforces a climate phenomenon called the Arctic Oscillation and steers frigid air southward to midlatitude regions throughout the winter…
The team’s analyses suggest that climate cycles such as the El Niño-Southern Oscillation, the Pacific Decadal Oscillation, and the Atlantic multidecadal oscillation can’t explain the regional cooling trends seen in the Northern Hemisphere during the past couple of decades as well as trends in Siberian snow cover do.