for National Geographic News
Summers in the Arctic Ocean may be ice free by 2040—decades earlier than previously expected, according to a new study of the effects of global warming on sea ice.
The scenario is predicted by computer models that assume greenhouse gas emissions will continue unabated.
Gases such as carbon dioxide spewed into the atmosphere by coal-fired power plants and automobiles are considered major drivers of global warming.
According to computer models, if the gases continue to build up in the atmosphere at the current rate, sea ice will steadily decline for decades and then abruptly disappear.
(Related news: "Arctic Ice Levels at Record Low, May Keep Melting, Study Warns" [October 3, 2005].)
"There are tipping points in the system," said Bruno Tremblay, an assistant professor of atmospheric and ocean sciences at McGill University in Montreal, Canada.
"When we reach them, things accelerate in a nonlinear way."
Tremblay is a co-author of the research, published today in the journal Geophysical Research Letters and presented on Monday at the fall meeting of the American Geophysical Union in San Francisco, California.
In the Arctic, the summer melt reduces ice cover to its minimum by September, when the arrival of winter usually refreezes the sea ice.
In one model simulation, September sea ice coverage will shrink from about 2.3 million square miles (6 million square kilometers) to 770,000 square miles (2 million square kilometers) in a span of ten years.
By 2040 only a small amount of sea ice will remain along the north coasts of Greenland and Canada, while most of the rest of the ocean basin will remain ice free through the summer (North America map).
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