Adam Morton
The Age, February 28, 2012
A DRAMATIC decline in Arctic sea ice linked to global warming is likely to have triggered record snow dumps in the northern hemisphere in recent winters, a study has found.
American and Chinese scientists found the drop in autumn Arctic sea ice - down by nearly a third since 1979 - caused changes in atmospheric circulation that contributed to freezing winters in China in 2007-08 and the US and Europe between 2009 and 2011.
In each case, large areas were hit by heavy snow, icy rain and cold temperatures that disrupted transport and energy supplies and damaged agriculture.
Study lead author Jiping Liu, a senior research scientist at the Georgia Institute of Technology, said the diminished Arctic ice cover led to weaker than usual westerly winds blowing across the Atlantic Ocean from Canada to Europe. ''It has made it easier for the cold Arctic air mass getting into mid and low-latitudes,'' he told The Age.
Published in US journal Proceedings of the National Academy of Sciences, the study also found the drop in sea ice and increase in open water had boosted the amount of moisture transferred from ocean to atmosphere, effectively giving it more snow to dump. ''If the Arctic sea ice continues to decline, probably we will see more consistent snow storms in the northern continents,'' Dr Liu said.
The decline in Arctic sea ice has outpaced climate models. The past five northern summers have been the five lowest for sea ice cover since satellite data was first collected in the 1970s - a reflection that Arctic temperatures have risen nearly twice as fast as the global average.
A US National Centre for Atmospheric Research computer simulation study recently estimated that about half of the ice loss between 1979 and 2005 was due to human greenhouse gas emissions and half natural variability.
Dr Liu said the study linking sea ice cover and extreme winter weather drew on both observational data and computer models that factored in snow cover, sea level pressure, surface air temperature and humidity.
He said the findings may help forecasting of snow and temperature anomalies.
US National Snow and Ice Data Centre director Mark Serreze has said that reports and aircraft reconnaissance indicated the recent summer sea ice levels were the lowest since 1900.
Analyses of ancient material have suggested it was likely to be at the lowest level since the end of the last glacial period about 8000 years ago.
The Arctic was ice free in the interglacial period about 125,000 years ago.
No comments:
Post a Comment