Thursday, September 06, 2012

What happens in the Arctic doesn't necessarily stay in the Arctic

What happens in the Arctic doesn't necessarily stay in the Arctic

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Between the drought and record-setting heat being experienced in so much of North America this summer, it’s unsurprising that few people here are thinking about sea ice in the Arctic. But we’re now entering the two- to three-week period during which the extent and volume of Arctic sea ice are typically at their minimum.

One thing is already certain--the previous record minimum for arctic sea ice has been broken. With half a month left in the melting season, the only question that remains is, how low can it go?

I checked in last week with William Chapman to contemplate that. Chapman is a senior research programmer in the U of I Department of Atmospheric Sciences whose work involves analyzing climate data from a variety of sources and teaching about arctic climate and meteorology.

Figures by William Champan/
University of Illinois Department of Atmospheric Sciences
As part of his work, he created and maintains a Website called, “The Cryosphere Today,” which brings together information from a variety of sources about weather and climate in the frozen parts of the world. The site is designed to provide information for anyone who might use it, and those who do include professional scientists, journalists and everyday people. It gets about 10,000 page views per day from all over the world.

To my disappointment—hey, I’m a writer—Chapman explained that record-setting events are not especially important in thinking about how weather and climate are changing in the Arctic. “That does not matter to me,” he said. “The key to thinking about what’s going on in the system is the long-term trend in summer sea ice.”

The satellite record tracking arctic sea ice dates back only to 1979. Up until about 2000, the trend is a fairly slow decline, but that decline gets steeper over the past decade.

 As you probably already know, the decline in sea ice matters immediately to both the people who inhabit the Arctic, and Arctic wildlife, including polar bears.

But the decline in Arctic ice also warms the Earth system as a whole, because open ocean absorbs so much more of the sun’s heat than ice and snow. (Ice and snow absorb only 20-30% of the sun’s energy, while ocean absorbs about 90%.) In winter, the blanket of sea ice that insulates the relatively warm ocean from the very cold air temperatures covers a smaller area. This allows even more heat to escape to the atmosphere.

Moreover, more warm ocean water in the late summer leads to slower regrowth of ice over the following winter. Says Chapman, “This is a very persistent system.”

Work done for a U of I Master’s thesis by Sara Strey suggests that changes in arctic sea ice might affect weather at the mid latitudes in the short term, too. She ran models comparing average arctic ice conditions with the extremely low conditions of 2007. Under the modeled 2007 conditions, the jet stream shifted, bringing colder-than-usual conditions to the U.S. in fall and early winter—exactly what we experienced.

While this line of research is young and the results are somewhat counterintuitive, there are strong indications that the Midwest may experience cooler autumns for the next few decades as sea ice continues to melt in the Arctic. That’s because, as Chapman said to me, “What happens in the arctic doesn’t necessarily stay in the arctic.”