New satellite records monitored by a national team of collaboratorsshow a four-year pattern of extremely low summer sea-ice coverage inthe Arctic that continued in September 2005, which may be the result ofwarming temperatures and earlier spring melting.
Since 2002, the satellite data have revealed unusually earlyspringtime melting in areas north of Siberia and Alaska. In 2005, thetrend expanded to include the entire Arctic ice pack, said Ted Scambosof CU-Boulder's National Snow and Ice Data Center, which led the studythat also involved NASA and the University of Washington.
The research group used the satellite record -- dating back to1978 -- to determine that the 2005 spring and summer melting beganabout 17 days earlier than usual, a new record. Average airtemperatures across most of the Arctic Ocean from January to August2005 were between 3.6 degrees F and 5.4 degrees F warmer than averagecompared to the last 50 years, said the team.
The conditions were followed by the lowest sea-ice extent yetseen in the satellite data, a five-day mean average of 2.06 millionsquare miles on Sept. 19. The team reported the extent was lower thanthe mean average September sea-ice extent from 1978 to 2001 by about 20percent, or 500,000 square miles, an area about twice the size ofTexas.
"Since the 1990s, The melting and retreat trends areaccelerating," said Scambos. "And the one common thread is that Arctictemperatures over the ice, ocean and surrounding land have increased inrecent decades."
The study was spearheaded by CU-Boulder's NSIDC and involvedNASA's Goddard Space Flight Center in Greenbelt, Md., NASA's JetPropulsion Laboratory in Pasadena and the University of Washington inSeattle. NSIDC is part of the Cooperative Institute for Research inEnvironmental Sciences, or CIRES, a joint program of CU-Boulder and theNational Oceanic and Atmospheric Administration.
The winter of 2004-2005 exhibited the smallest recovery ofArctic sea ice of any previous winter in the 23-year satellite record,the group reported. With the exception of May 2005, every month sinceNovember 2004 has exhibited the lowest monthly average of sea-iceextent since satellite record-keeping began in the region.
Although sea-ice records prior to 1978 are comparativelysparse, they imply the recent decline exceeds previous sea-ice lows,said Julienne Stroeve of CU-Boulder's NSIDC. "Considering therecord-low amounts of sea-ice this year leading up to the month ofSeptember, 2005 could surpass 2002 as the lowest amount of sea-icecover in more than a century," she said.
Arctic sea ice typically reaches a minimum in September at theend of the summer melt season. The trend of Arctic sea ice declinedocumented by satellites is now about 8.4 percent per decade since the1970s, the group reported.
Scientists believe the Arctic Oscillation, a major atmosphericcirculation pattern that can push sea ice out of the Arctic, may havecontributed to the sea-ice reduction in the mid-1990s by making it morevulnerable to summertime melt, said CU-Boulder's Mark Serreze of NSIDC.While the pattern has become less of an influence on the region sincethe late 1990s, the sea ice has continued to decline.
"Something has fundamentally changed here, and the best answer is warming," Serreze said.
The decline is likely to affect future temperatures in theArctic, since ice acts as a cooling mechanism to reflect most of thesun's radiation back into space, Scambos said. As sea ice melts, largerareas of darker ocean decrease the amount of solar energy reflectedaway from Earth.
"Feedbacks in the system are starting to take hold," Scambossaid. "The consecutive record-low extents make it pretty certain along-term decline is underway."
Arctic sea ice consists of both annual ice and multi-yearice. The multi-year ice has been declining at almost 10 percent perdecade, said Florence Fetterer of CU-Boulder's NSIDC. While a recoveryof multi-year ice would require sustained cooling in the Arctic,especially during the summer months, climate models predict continuedArctic warming, she said.
The researchers used satellite data from NASA, the National Oceanicand Atmospheric Administration and the U.S. Department of Defense, aswell as data from Canadian satellites and weather observatories.
Note to Editors: Images and further information available 9/28/05 at: http://nsidc.org/news/press/20050928_trendscontinue.html
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