Do the Hot and Cold Spells Have a Meaning?
Can extreme weather events like this weekend's historic outbreak of cold Arctic air across the U.S. be caused by the warming of the Arctic?
Though it seems counterintuitive – global warming bringing about extreme cold – the answer may be yes, according to scientists like Weather Underground's Dr. Jeff Masters and Dr. Jennifer Francis, a research professor at Rutgers University's Institute of Marine and Coastal Sciences.
The cause is believed to lie in the jet stream, the fast-flowing river of air high above the Earth that marks the boundary between cold, polar air to the North and warm tropical air to the South.
As the jet stream shifts position back and forth over North America throughout the year, it plays a major role in the weather patterns and temperatures we experience in the U.S. In recent years, the movement of the jet stream has changed significantly, bringing "weather whiplash" with strange, out-of-season weather events more frequently than in the recent past.
Francis has been a leading voice in recent years for research that points to rapid changes in the Arctic – including a dramatic decline over the past 30 years in Arctic sea ice extent, which exposes more of the Arctic Ocean to the sun's rays in the summer – as the likely culprit behind the jet stream's increasingly odd behavior.
Average Monthly Arctic Sea Ice Extent in November, 1978-2013
NSIDC Including 2013, the linear trend in November ice extent is –4.9 percent per decade relative to the 1981 to 2010 mean, or a loss of about 20,700 square miles per year. (Courtesy National Snow and Ice Data Center)
The cause is thought to be what scientists call Arctic amplification, the tendency of the polar region to experience more warming (and at a faster pace) than the rest of the Northern hemisphere. This heightened sensitivity is due to the Arctic's snow cover and sea ice, and the feedback loops triggered by their presence (or absence).
"As sea ice retreats, sunshine that would have been reflected back to space by the bright ice is instead absorbed by the ocean, which heats up, melting even more ice," Francis explained in a March 2012 article at Yale360.
"Extra heat entering the vast expanses of open water that were once covered in ice is released back to the atmosphere in the fall," she adds. "All that extra heat being deposited into the atmosphere cannot help but affect the weather, both locally and on a large scale."
Why? Because the Arctic is warming so quickly – about twice as fast as as the rest of the planet – the difference in temperature between the Arctic and the lower latitudes is narrowing.
That temperature difference drives the jet stream; when it shrinks, the jet stream slows and undulates more. It also moves more north-south than east-west (its usual flow), and can get stuck in patterns that last for much longer than they did even a few years ago.
And when that happens, the waves of the jet stream slow down and become larger and more sluggish. When they increase in size thanks to Arctic amplification, they move eastward more slowly, allowing the weather associated with them to stick around longer.
Still, not all climate scientists accept the linkages between long-term global warming, thinning Arctic sea ice, and weather events like this weekend's. The science around attributing weather events at lower latitudes to what happens in the Arctic is still very new, and scientists are far from consensus on whether such a link exists.
In August, a study published by Elizabeth Barnes of Colorado State University called into question Francis' research that links Arctic amplification with the recent changes in the jet stream. And In September, the National Academy of Sciences convened a workshop that drew dozens of climate scientists from around the world to discuss this topic.
But the possibility between what's occurring in the Arctic and what happens when extreme weather hits will undoubtedly continue to receive an increasing amount of attention.
For more, hear Dr. Jeff Masters and Jennifer Francis talk more about how Arctic warming is changing weather in the U.S. in this video:
ORIGINAL: Weather Channel
By Terrell Johnson
Jan 6, 2014
