Friday, October 5, 2007

Decline In Arctic Sea Ice Caused By Unusual Winds, Not Warming

The supposedly drastic and unusual melting of Arctic sea ice this past summer has made the news recently. The cause has always been attributed to global warming, which many people want us to believe is caused by man's carbon dioxide emissions.

However, here is an alternative theory. Scientists at NASA now say the disappearance of the ice may be caused by unusual winds, not purely warming. I wonder if they have told Global Warming Jim Hansen about this?

Recent Rapid Decline in Arctic Sea Ice caused by Unusual Winds, says NASA
Post below lifted from Accuweather. See the original for links and graphics
In a news release from NASA Monday, a group of scientists have determined that unusual winds caused the rapid decline (23% loss) in winter perennial ice over the past two years in the northern hemisphere. This drastic reduction is the primary cause of this summer's fastest-ever sea ice retreat in recorded history which has lead to the smallest extent of total Arctic coverage on record.

According to the NASA study, the perennial ice shrunk by an area the size of Texas and California combined between the winter of 2005 and the winter of 2007. What they found was the Arctic Ocean north of Siberia and Alaska was dominated by thinner seasonal ice that melts faster compared to the thicker ice confined to the Arctic Ocean north of Canada. The thinner ice is more easily compressed and responds more quickly to being pushed out of the Arctic by winds.

"Unusual atmospheric conditions set up wind patterns that compressed the sea ice, loaded it into the Transpolar Drift Stream and then sped its flow out of the Arctic," said Son Nghiem of NASA's Jet Propulsion Laboratory and leader of the study. When that sea ice reached lower latitudes, it rapidly melted in the warmer waters. What about these unusual wind patterns. Well, the article does not go into that too much, but I must believe some of this is due to changes in the Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) which are large atmospheric circulations which have major impacts on the weather in certain parts of the world.

If you look at the two graphics below, you will notice that both the AO and the NAO have been predominately in the positive phase (red) between 1989-1995 and again from 1999 to current. The positive phase of the (AO) typically leads to milder than normal winters over Scandinavia and Siberia, while colder than normal conditions prevail across Greenland. The positive phase of the NAO again leads to colder conditions over Greenland, while much of the eastern U.S. is warmer than normal in general.

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