The current warming trends in the Arctic may shove the Arcticsystem into a seasonally ice-free state not seen for more than onemillion years, according to a new report. The melting is accelerating,and a team of researchers were unable to identify any natural processesthat might slow the de-icing of the Arctic.
Such substantialadditional melting of Arctic glaciers and ice sheets will raise sealevel worldwide, flooding the coastal areas where many of the world'speople live.
Melting sea ice has already resulted in dramaticimpacts for the indigenous people and animals in the Arctic, whichincludes parts of Alaska, Canada, Russia, Siberia, Scandinavia andGreenland.
“What really makes the Arctic different from the restof the non-polar world is the permanent ice in the ground, in the oceanand on land,” said lead author University of Arizona geoscientistJonathan T. Overpeck. “We see all of that ice melting already, and weenvision that it will melt back much more dramatically in the future aswe move towards this more permanent ice-free state.”
The reportby Overpeck and his colleagues is published in the Aug. 23 Eos, theweekly newspaper of the American Geophysical Union. A complete list ofauthors and their affiliations is at the end of this release.
Thereport is the result of weeklong meeting of a team of interdisciplinaryscientists who examined how the Arctic environment and climate interactand how that system would respond as global temperatures rise. Theworkshop was organized by the NSF Arctic System Science Committee,which is chaired by Overpeck. The National Science Foundation fundedthe meeting.
The past climates in the Arctic include glacialperiods, where sea ice coverage expanded and ice sheets extended intoNorthern America and Europe, and warmer interglacial periods duringwhich the ice retreats, as it has during the past 10,000 years.
Bystudying natural data loggers such as ice cores and marine sediments,scientists have a good idea what the “natural envelope” for Arcticclimate variations has been for the past million years, Overpeck said.
Theteam of scientists synthesized what is currently known about the Arcticand defined key components that make up the current system. Thescientists identified how the components interact, including feedbackloops that involve multiple parts of the system.
“In the past,researchers have tended to look at individual components of theArctic,” said Overpeck. “What we did for the first time is really lookat how all of those components work together.”
The team concludedthat there were two major amplifying feedbacks in the Arctic systeminvolving the interplay between sea and land ice, ocean circulation inthe North Atlantic, and the amounts of precipitation and evaporation inthe system.
Such feedback loops accelerate changes in the system,Overpeck said. For example, the white surface of sea ice reflectsradiation from the sun. However, as sea ice melts, more solar radiationis absorbed by the dark ocean, which heats up and results in yet moresea ice melting.
While the scientists identified one feedbackloop that could slow the changes, they did not see any naturalmechanism that could stop the dramatic loss of ice.
“I thinkprobably the biggest surprise of the meeting was that no one couldenvision any interaction between the components that would actnaturally to stop the trajectory to the new system,” Overpeck said. Headded that the group investigated several possible braking mechanismsthat had been previously suggested.
In addition to sea and landice melting, Overpeck warned that permafrost—the permanently frozenlayer of soil that underlies much of the Arctic—will melt andeventually disappear in some areas. Such thawing could releaseadditional greenhouse gases stored in the permafrost for thousands ofyears, which would amplify human-induced climate change.
Overpecksaid humans could step on the brakes by reducing carbon dioxideemissions. “The trouble is we don’t really know where the threshold isbeyond which these changes are inevitable and dangerous," Overpecksaid. “Therefore it is really important that we try hard, and as soonas we can, to dramatically reduce such emissions.”
Overpeck’scoauthors on the Aug. 23 Eos paper are Matthew Sturm of the ColdRegions Research and Engineering Laboratory in Fort Wainwright, Alaska;Jennifer A. Francis of Rutgers University in New Brunswick, N.J.;Donald K. Perovich of the Cold Regions Research and EngineeringLaboratory in Hanover, N.H.; Mark C. Serreze of the University ofColorado, Boulder; Ronald Benner of the University of South Carolina inColumbia; Eddy C. Carmack of the Institute of Ocean Sciences in Sidney,BC, Canada; F. Stuart Chapin III of the University of Alaska,Fairbanks; S. Craig Gerlach of the University of Alaska, Fairbanks;Lawrence C. Hamilton of the University of New Hampshire in Durham;Larry D. Hinzman of the University of Alaska, Fairbanks; Marika Hollandof the National Center for Atmospheric Research in Boulder, Colo.;Henry P. Huntington of Huntington Consulting in Eagle River, Alaska;Jeffrey R. Key of the National Oceanic and Atmospheric Administration’sNational Environmental Satellite, Data, and Information Service inMadison, Wis.; Andrea H. Lloyd of Middlebury College in Middlebury,Va.; Glen M. MacDonald of the University of California, Los Angeles;Joe McFadden of the University of Minnesota in St. Paul; David Noone ofthe California Institute of Technology in Pasadena, Calif.; Terry D.Prowse of the University of Victoria, in BC, Canada; Peter Schlosser ofColumbia University in Palisades, N.Y.; and Charles Vφrφsmarty of theUniversity of New Hampshire in Durham.
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