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Arctic's loss of sea ice sets record

Scientists say the retreat of snow and ice shows the self-perpetuating momentum of global warming.

December 05, 2012|By Kenneth R. Weiss, Los Angeles Times
  • Arctic sea ice is seen from a NASA plane. Arctic sea ice retreated to a record minimum since scientists began to measure it with satellites in 1979.
Arctic sea ice is seen from a NASA plane. Arctic sea ice retreated to a record… (Michael Studinger, European…)

A fast-changing Arctic broke new records for loss of sea ice and spring snow cover this year, as well as the extent of the summertime melt of the Greenland ice sheet, federal scientists reported Wednesday.

The latest report about the melting Arctic comes as frustrations flared in Doha, Qatar, over the slow progress at United Nations climate talks to reach a global agreement on reducing emissions of greenhouse gases. The buildup of the gases is elevating average global temperatures, with the most pronounced changes in the northernmost latitudes.

"The Arctic is an extremely sensitive part of the world," said Jane Lubchenco, administrator of the National Oceanic and Atmospheric Administration. As it warms, she said, "we see the results with less snow and sea ice, greater ice sheet melt and changing vegetation."

Speaking at the fall meeting of the American Geophysical Union in San Francisco, Lubchenco and other scientists unveiled the annual update of the Arctic Report Card, a collaboration of more than 140 scientists that summarizes ways the Arctic continues to grow warmer and greener.

Among this year's findings:

• The Arctic sea ice retreated to a record minimum since scientists began to measure it with satellites in 1979. The ice sheet is about half of what it was in 2000. The loss of sea ice is important to the survival of ring seals, walruses, polar bears and other animals.

•The Greenland ice sheet experienced the most widespread melt on record, covering about 97% of the ice sheet on a single day in July. The accelerating melt of this vast frozen repository of fresh water is the wild card in scientific projections of how much and how fast sea levels will rise in coming decades.

• A new record low for snow cover in the Northern Hemisphere was set in June. Much of the high-latitude landscape has snow covering it for nine months of the year. Although some years are snowier than others, its overall retreat is altering spring river runoff, growing seasons and the behavior of wildlife.

• With longer growing seasons, the tundra is getting greener and the underlying permafrost is thawing. Shrubs are spreading, as is the frequency of tundra wildfires.

The retreat of snow and ice has come even though Arctic air temperatures were not unusually high this year compared with the last decade, the scientists reported.

This shows the self-perpetuating momentum of warming, they said. As the Arctic loses more highly reflective snow and ice, the warming rays of the sun get absorbed by the darker ground or exposed ocean waters.

"This increases the capacity to store heat within the Arctic system, which enables more melting — a self-reinforcing cycle," said Martin Jeffries, co-editor of the report card and a science advisor to the Office of Naval Research.

ken.weiss@latimes.com

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