October 31, 2008
Climate Change Altering World Landscape
Human activities are making both Antarctica and the Arctic less icy because of global warming, scientists said on Thursday.
An international team published their findings in the recent Nature Geoscience journal.
"We're able for the first time to directly attribute warming in both the Arctic and the Antarctic to human influences," said Nathan Gillett of England's University of East Anglia of a study he led with colleagues in the United States, Britain and Japan.
The research team measured temperature changes over the polar regions of the Earth and compared them with two sets of climate models. One set assumed that there had been no human influence the other set assumed there had.
The best fit was with models that assumed that human activities including the burning of fossil fuels and depletion of ozone had played a part.
Researcher Peter Stott, head of climate monitoring and attribution at the Met Office, said scientifically showing the Antarctic was influenced by human activities was the significant development.
"In the recent IPCC report for example," he said, "it wasn't possible to make a statement about the Antarctic because such a study had not been done at that point.
"But nevertheless when you do that you see a clear human fingerprint in the observed data. We really can't claim anymore that it's natural variations that are driving these very large changes that we are seeing in our in the climate system."
In recent years, the Arctic has warmed sharply and sea ice shrank in 2007 to a record low.
But researchers say Antarctic trends have been confusing because some winter sea ice has expanded in recent decades, leaving doubts for some about whether warming was global.
The U.N. Climate Panel, which draws on work by 2,500 experts, said in 2007 that the human fingerprint on climate "has been detected in every continent except Antarctica," which has insufficient observational coverage to make an assessment.
The link with human activities had been elusive in polar-regions because there are fewer than 100 temperature stations in the Arctic and just 20 in Antarctica.
The scientists said temperatures in the Artic had increased 2 Celsius (3.6 Fahrenheit) in the past 40 years.
Temperatures in Antarctica, an icy deep freeze bigger than the United States, had gained by a few tenths of a degree.
The human cause had been hinted at by the U.N. Climate Panel last year, which said a human impact "has likely contributed to recent decreases in Arctic sea ice extent."
Professor Phil Jones, director of the Climate Research Unit at the University of East Anglia, said, "Our study is certainly closing a couple of gaps in the last IPCC report.
"But I still think that a number of people, including some politicians, are reluctant to accept the evidence or to do anything about it until we specifically come down to saying that one particular event was caused by humans like a serious flood somewhere or even a heat wave.
"Until we get down to smaller scale events in both time and space I still think there will be people doubting the evidence."
Scientists urged additional study of ice and temperatures.
The U.N. Climate Panel projects that sea levels will rise by between 18 and 59 cm this century, part of shifts also likely to include more droughts, floods, heat waves and more destructive storms.
"We really need to pay closer attention to what's going on with these ice sheets," said Andrew Monaghan, of the U.S. National Center for Atmospheric Research.
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