A new analysis supports a growing body of research suggesting that thick, old Arctic sea ice is being replaced by young, thin ice that is susceptible to the ongoing summer warming expected with global warming. There has been a nearly complete loss of the oldest, thickest ice, according to the study.
Since 1982, the extent of thick sea ice, built up, layer by layer, year after year, is decreasing in favor of thin seasonal ice. The 25-year trend was described in Geophysical Research Letters by University of Colorado at Boulder scientists. The researchers used satellite data to reconstruct past ice conditions. Of the ice that remains, 58% is no more than two to three years old, compared to 35% in the mid-1980s.
Authors of the study said it was the first "to quantify the magnitude of the Arctic sea ice retreat using data on the age of the ice and its thickness."
"This thinner, younger ice makes the Arctic much more susceptible to rapid melt," lead author James Maslanik said in a prepared statement. "Our concern is that if the Arctic continues to get kicked hard enough toward one physical state, it becomes increasingly difficult to reestablish the sea ice conditions of 20 or 30 years ago."
The extent of Arctic sea ice in 2007 reached a record low, 23% more extreme than the previous record, set just two years earlier. At that time, the 2005 record seemed extraordinary, but another 1 million square miles melted in 2007, compared to the previous record in 2005.
The portion of ice more than five years old within the multi-year Arctic icepack decreased from 31% in 1988 to 10% in 2007, according to the study. Ice 7 years or older, which made up 21% of the multi-year Arctic ice cover in 1988, made up only 5% in 2007.
"Taken together, these changes suggest that the Arctic Ocean is approaching a point where a return to pre-1990s ice conditions becomes increasingly difficult and where large, abrupt changes in summer ice cover as in 2007 may become the norm," the research team wrote in Geophysical Research Letters.
Here's how the University of Colorado at Boulder described the research:
The researchers used passive microwave, visible infrared radar and laser altimeter satellite data from the National Oceanic and Atmospheric Administration, NASA and the U.S. Department of Defense, as well as ocean buoys to measure and track sections of sea ice.
The team developed "signatures" of individual ice sections roughly 15 miles square using their thickness, roughness, snow depth and ridge characteristics, tracking them over the seasons and years as they moved around the Arctic via winds and currents. ...
The replacement of older, thicker Arctic ice by younger, thinner ice, combined with the effects of warming, unusual atmospheric circulation patterns and increased melting from solar radiation absorbed by open waters in 2007 all have contributed to the phenomenon, said Drobot.
"These conditions are setting the Arctic up for additional, significant melting because of the positive feedback loop that plays back on itself," said co-author Sheldon Drobot.
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