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December 08, 2013

Study Links Arctic Melting, Extreme Weather

by Steve Baragona

As ice at the North Pole disappears at an alarming rate, researchers are finding a link with recent bouts of extreme weather.

A new study suggests rapid warming in the Arctic may be altering weather patterns across the Northern Hemisphere.

But skeptics say the case is far from proven.

An “unbelievable amount of change” is happening in the Arctic, says Rutgers University climate scientist Jennifer Francis. Just half as much area is covered by ice compared to 30 years ago.

“And if you take into account the thickness as well, we’ve lost almost three-quarters of the volume of the sea ice,” she said.

Melting ice, heat waves

At the same time, the Northern Hemisphere has seen some unbelievable weather in the last decade: Record-breaking heat waves and droughts in North America and Europe, and devastating floods in East Asia, to name a few.

Francis and colleagues went back through three decades of weather data and measurements of Arctic ice and snow cover in northern latitudes. They found that, “when there was less ice or less snow in any given year during the summertime, that that was more likely to occur at the same time as the occurrences of heat waves,” she says.

They published their findings in Nature Climate Change. 

Weaker jet stream

Francis says the loss of ice and snow are affecting the high-altitude wind patterns called the jet stream, which push weather patterns around the Northern Hemisphere.

The jet stream is driven by the difference in temperature between the Arctic and the temperate zones. The bigger the difference, the faster the jet stream flows.

But Francis notes that the Arctic is warming at least twice as fast as the rest of the planet.

“If we warm the arctic faster,” she said, “it’s decreasing the temperature difference and causing the jet stream to get weaker.”

Weaker and wavier

And a weaker jet stream is wavier, she says. Think of a stream flowing down a mountain. The steeper the height difference, the faster and straighter it runs. On level ground, that stream can meander.

As the jet stream meanders, Francis adds, it pulls hot weather up from the tropics or cold weather down from the Arctic.

“As these waves get larger, they tend to move more slowly from west to east. So, whatever weather they’re causing down at the surface also changes more slowly.”

And that means heat waves, cold snaps and rainstorms can last longer.

Unproven link

This theory has only been around for a couple years, and University of Exeter climate scientist James Screen is one of those who are not convinced.

Screen says the new study only shows a few scattered areas of the globe where the link between sea ice loss and heat waves is significant, according to mathematical tests, “which implies either that the relationship is quite weak, or actually, it could be interpreted that the relationship doesn’t exist at all.”

“It could be true,” he said, “but at the moment I don’t think the evidence is there to really strongly argue the case.”

National Oceanic and Atmospheric Administration climate researcher James Overland says he’s “pretty much in the middle ground on how proven it is.” But, he adds, “certainly something’s going on that needs a closer look.”

Overland wrote a commentary accompanying the article. In it, he says better understanding of how the changing Arctic affects global weather could help improve forecasting.

That’s increasingly important, he notes, because global greenhouse gas emissions will continue to melt the Arctic for decades to come.

“The loss of sea ice will go from 50 percent to 100 percent in the next 20 years or so,” he said. “We’re just going to have a whole lot more fuel for the atmosphere to use up."

And one way or another, he says, "it’ll end up with the increased chance of more of these extreme events down here where people live.”