Melting Arctic ice will bring colder winters
As Arctic sea ice melts through global warming, Americans can expect - paradoxically - to see more severe winter weather.
"Everyone thinks of Arctic climate change as this remote phenomenon that has little effect on our everyday lives," says Charles H Greene of Cornell University. "But what goes on in the Arctic remotely forces our weather patterns here."
As sea ice melts during summer, it exposes darker ocean water to incoming sunlight. This causes increased absorption of solar radiation and greater heating of the ocean in summer – further accelerating the ice melt.
The excess heat is released to the atmosphere, especially during the autumn, bringing the temperature and atmospheric pressure in the Arctic and middle latitudes closer together.
This lowering in the pressure gradient weakens the winds associated with the polar vortex and jet stream - and as the polar vortex normally retains cold Arctic air up above the Arctic Circle, its weakening allows it to invade lower latitudes.
"What's happening now is that we are changing the climate system, especially in the Arctic, and that's increasing the odds for the negative AO conditions that favor cold air invasions and severe winter weather outbreaks," says Greene. "It's something to think about, given our recent history."
While this past winter was one of the warmest recorded in the eastern US, there have been record snow storms in the region over the last two years.
"It's a great demonstration of the complexities of our climate system and how they influence our regional weather patterns," says Greene.
This winter, La Nina in the Pacific shifted undulations in the jet stream so that while many parts of the Northern Hemisphere were hit by severe winter weather patterns, much of the eastern US was warmed by the warm tropical air that swung north with the jet stream.
But Europe and Alaska experienced record-breaking winter storms, and the global average temperature during March 2012 was cooler than any other March since 1999.
"A lot of times people say, 'Wait a second, which is it going to be – more snow or more warming?' Well, it depends on a lot of factors, and I guess this was a really good winter demonstrating that," says Greene.
"What we can expect, however, is the Arctic wildcard stacking the deck in favor of more severe winter outbreaks in the future."