Linking Weird Weather to Rapid Warming of the Arctic
Posted by Daniel Bailey, Skeptical Science, April 13, 2012
NOTE: This post is reprinted from an article originally appearing in Yale Environment 360, by permission of the author, Dr. Jennifer Francis and Yale Environment 360.
Arctic amplification describes the tendency for high Northern latitudes to experience enhanced warming or cooling relative to the rest of the Northern Hemisphere. This heightened sensitivity is linked to the presence of snow and sea ice, and the feedback loops that they trigger. For example, 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. As the world has warmed since the fossil-fuel revolution after World War II, Arctic temperatures have increased at more than twice the global rate. A dramatic indicator of this warming is the loss of Arctic sea ice in summer, which has declined by 40% in just the past three decades. The area of lost ice is about 1.3 million square miles, or roughly 42% of the area of the Lower 48 United States.
Extra heat entering the vast expanses of open water that were once covered in ice is released back to the atmosphere in the fall. This has led to an increase in near-surface, autumn air temperatures of 2-5 C (3.6-9 F) over much of the Arctic Ocean during the past decade.
But if so, how does it work?
The second way that Arctic amplification is expected to influence the jet stream and our weather is by increasing the “waviness” of the jet stream. Because of Arctic amplification, the northern peaks of waves, called ridges, will experience more warming than the southward dips, called troughs. This is expected to cause the ridges to stretch northward, which will increase the size of the waves. Larger swings in the jet stream allow frigid air from the Arctic to plunge farther south, as well as warm, moist tropical air to penetrate northward. These wavy flows often lead to record-breaking temperatures. Meteorologists have also known for a long time that larger jet-stream waves progress eastward more slowly, as will the weather systems associated with them. Consequently this represents another mechanism that will cause weather conditions to linger.
Increased waviness seems to be occurring during summer, as well, but instead of sea ice loss, the culprit appears to be the progressively earlier melt of snow on Arctic and sub-Arctic land in the spring.
There have been many examples of “stuck” weather patterns during the past few years. Deep troughs in the jet stream hung over the U.S. east coast and Western Europe during the winters of 2009/2010 and 2010/2011, bringing a seemingly endless string of snow storms and teeth-chattering cold. In the early winter of 2011/2012, in contrast, these same areas were under ridges, or northward bulges of the jet stream, which brought unusually warm and snowless conditions over much of North America. At the same time, however, a deep trough sat over Alaska, dumping record snows. In early February this year, the jet stream plunged unusually far southward over Europe, bringing frigid Arctic air and snow to some areas that hadn’t seen those conditions in over half a century. During summer, persistent weather patterns are responsible for droughts and heat. The record heat waves in Europe and Russia in the past several years have been linked to early snowmelt in Siberia, and a sluggish high-pressure area caused last summer’s sweltering conditions in the south-central U.S.
While it’s difficult to point the finger at Arctic amplification in causing any of these weather events, they are the types of phenomena that are expected to occur more frequently as the world continues to warm and the Arctic continues to lose its ice. Further research may find ways to predict which regions will experience which conditions. But in the meantime, it’s increasingly likely that the weather you have today will stick around awhile.