Wednesday, April 29, 2015

Arctic Sea Ice is Disappearing

Arctic sea ice has been getting smaller and thinner as part of a general decline witnessed over the past four decades. In recent years Arctic sea ice has reached the lowest level ever recorded, shrinking to less than half the area it occupied a few decades ago.

Maximums

In 2015 Arctic sea ice maximum was the smallest on record. This information comes from satellite data produced by NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado, Boulder. On February 25th there were 5.61 million square miles (14.54 million square kilometers) of sea cap ice. That is 50,000 square miles below the previous lowest peak wintertime extent. It is both the earliest and the smallest maximum amount of floating ice on top of the Arctic Ocean since record taking began in 1979.

Minimums

The lowest minimum extent has also occurred in recent years. In 2012 there was only 1.31 million square miles of ice. That is about 300,000 square miles, or 18.6 percent smaller than the previous record low of 1.61 million square miles in 2007.

Thinning

These observations are part of a trend of declining Arctic sea ice. In fact according to a study published in an issue of journal The Cryosphere Arctic sea ice is thinning at a steadier and faster rate than researchers had previously thought. This study was unique in that it used modern and historic measurements including satellite, submarine and direct measurement. This research showed that ice in the central Arctic Ocean thinned 65 percent between 1975 and 2012. During that time it has decreased by 7.6 feet. It went from 11.7 feet (3.59 meters) in 1975 to 4.1 feet (1.25 m) 2012.

In the month of September when sea-ice levels are at their lowest historical records show ice thickness thinned by 85 percent between 1975 and 2012. During this 37-year period ice thickness went from 9.8 feet (3.01 m) to 1.4 feet (0.44 m). The seven lowest September sea ice extents in the satellite record have all occurred in the past seven years.

"The ice is thinning dramatically," said lead researcher Ron Lindsay, a climatologist at the University of Washington (UW) Applied Physics Laboratory. "We knew the ice was thinning, but we now have additional confirmation on how fast, and we can see that it's not slowing down."

Melting

The period during which the Arctic ice melts is currently 15 days longer than it was 30 years ago. Melting starts earlier and ends later. The overall trend indicates that it is growing by several days each decade. For example the Beaufort and Chukchi Seas, are freezing up between six and 11 days later per decade. This has a feedback effect because open Arctic waters absorb solar radiation and cause more melting. These are the findings in a study by National Snow and Ice Data Center (NSIDC) and NASA researchers.

"The Arctic is warming and this is causing the melt season to last longer," said Julienne Stroeve, a senior scientist at NSIDC, Boulder and lead author of the new study. "The lengthening of the melt season is allowing for more of the sun’s energy to get stored in the ocean and increase ice melt during the summer, overall weakening the sea ice cover."

End of Summer Ice

The Arctic sea ice is shrinking at the rate of approximately 13 percent per decade and it is expected that by the summer of 2030 it will disappear completely. 

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