‘Arctic wildcard stacking the deck in favor of more severe winter outbreaks‘
By Summit Voice
SUMMIT COUNTY — Evidence continues to mount that melting Arctic ice is having a significant effect in the mid-latitudes, where most people live, and it’s not something that’s going to take decades to develop.
Instead, researchers say, the warming of the high latitudes has decreased a historic pressure gradient at the boundary of the high- and mid latitudes. Basically, the pressure difference has decreased, and that is having a fundamental effect on the way the jet stream moves from west to east in the northern hemisphere.
The jet stream is a high-elevation, high-speed river of air that drives storm systems. Historically, there are variations in the flow of the jet stream, which also influenced by seasonal and decadal variations in sea surface temperatures and other factors.
As the Arctic thaws, that prevailing westerly flow has slowed measurably, by 20 percent in the past few decades.
This past winter, Rutgers University researcher Jennifer Francis called these changes the “revenge of the atmosphere,” while giving a climate and weather presentation in Breckenridge, Colorado.
“Everyone thinks of Arctic climate change as this remote phenomenon that has little effect on our everyday lives,” said Cornell University’s Charles H. Greene. “But what goes on in the Arctic remotely forces our weather patterns here.”
Greene is the latest to outline the links between the Arctic meltdown and weather in North America, Europe and Asia in a paper published in the June issue of the journal Oceanography.
The additional Arctic heat from the darker colored ocean is released to the atmosphere, especially during the autumn, decreasing the temperature and atmospheric pressure gradients between the Arctic and middle latitudes.
The polar vortex normally retains the cold Arctic air masses up above the Arctic Circle, but its weakening allows the cold air to invade lower latitudes.
The recent observations present a new twist to the Arctic Oscillation – a natural pattern of climate variability in the Northern Hemisphere. Before humans began warming the planet, the Arctic’s climate system naturally oscillated between conditions favorable and those unfavorable for invasions of cold Arctic air.
“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 “Arctic Oscillation conditions that favor cold air invasions and severe winter weather outbreaks,” Greene said. “It’s something to think about given our recent history.”
This past winter, central and Eastern Europe were gripped by extreme cold in mid-January, with temperatures approaching minus 22 degrees Fahrenheit and snowdrifts reaching rooftops. And there were the record snowstorms fresh in the memories of residents from several eastern U.S. cities, such as Washington, New York and Philadelphia, as well as many other parts of the Eastern Seaboard during the previous two years.
Greene and Monger did note that their paper is being published just after one of the warmest winters in the eastern U.S. on record.
Francis said the changes slow the progression of low pressure troughs and high pressure ridges, potentially explaining the extended spell of extremely mild weather across the U.S. this past winter.
“It’s a great demonstration of the complexities of our climate system and how they influence our regional weather patterns,” Greene said.
In any particular region, many factors can have an influence, including the El Nino/La Nina cycle. 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 the severe winter weather patterns expected during a bout of negative AO conditions, much of the eastern United States basked in the warm tropical air that swung north with the jet stream.
“It turns out that while the eastern U.S. missed out on the cold and snow this winter, and experienced record-breaking warmth during March, many other parts of the Northern Hemisphere were not so fortunate,” Greene said.
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,” Greene said. “What we can expect, however, is the Arctic wildcard stacking the deck in favor of more severe winter outbreaks in the future.”