From: Allison Winter, ENN
Published May 8, 2014 06:48 AM

Climate Change vs. Natural Variations: Why is Greenland Melting?

The climate change debate continues. Are anthropogenic causes of global warming responsible for melting ice and rising seas or are natural cycles and climate variations to blame?

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There's no question that Greenland's glaciers are in fact melting. And while the obvious culprit may be global warming caused by rising carbon dioxide emissions, University of Washington atmospheric scientists have estimated that up to half of the recent warming in Greenland and surrounding areas may be due to climate variations.

The kicker? These climate variations originate in the tropical Pacific and are not connected with the overall warming of the planet.

Greenland and parts of neighboring Canada have experienced some of the most extreme warming since 1979 - warming at a rate of about 1 degree Celsius per decade, which is several times the global average.

In an attempt to understand why global warming has not been uniform across the globe, UW researchers conducted a study using observations and advanced computer models to explain why regional warming, specifically in Greenland, may be occurring. 

The study shows that a warmer western tropical Pacific Ocean has caused atmospheric changes over the North Atlantic that have warmed the surface by about a half-degree per decade since 1979.

"The pattern of the changes in the tropical Pacific that are responsible for remarkable atmospheric circulation changes and warming in Greenland and the Canadian Arctic are consistent with what we would call natural variability," said co-author David Battisti, a UW professor of atmospheric sciences.

Researchers say it's not surprising to find the imprint of natural variability in an area famous for its melting ice. In many of the fastest-warming areas on Earth, global warming and natural variations both contribute to create a "perfect storm" for warming, said co-author John "Mike" Wallace, a UW professor of atmospheric sciences.

The natural variations in new study related to an unusually warm western tropical Pacific, near Papua New Guinea. Since the mid-1990s the water surface there has been about 0.3 degrees hotter than normal. Computer models show this affects the regional air pressure, setting off a stationary wave in the atmosphere that arcs in a great circle from the tropical Pacific toward Greenland before turning back over the Atlantic.

"Along this wave train there are warm spots where the air has been pushed down, and cold spots where the air has been pulled up," Wallace said. "And Greenland is in one of the warm spots."

Researchers can't say for how long the tropical Pacific will remain in this state.

The paper is published today in Nature.

Read more about the study at the University of Washington.

Greenland image via Shutterstock.

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