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November 27, 2002
THE ARCTIC PERENNIAL SEA ICE COULD BE GONE BY END OF THE CENTURY
A NASA study finds that perennial sea ice in the Arctic is melting faster than previously thought—at a rate of 9 percent per decade. If these melting rates continue for a few more decades, the perennial sea ice will likely disappear entirely within this century, due to rising temperatures and interactions between ice, ocean and the atmosphere that accelerate the melting process.
Perennial sea ice floats in the polar oceans and remains at the end of the summer, when the ice cover is at its minimum and seasonal sea ice has melted. This year-round ice averages about 3 meters (9.8 feet) in depth, but can be as thick as 7 meters (23 feet).
The study also finds that temperatures in the Arctic are increasing at the rate of 1.2 degrees Celsius (2.2 Fahrenheit) per decade.
Melting sea ice would not affect sea levels, but it could profoundly impact summer shipping lanes, plankton blooms, ocean circulation systems, and global climate.
“If the perennial ice cover, which consists mainly of thick multi-year ice floes, disappears, the entire Arctic Ocean climate and ecology would become very different,” said Josefino Comiso, a researcher at NASA’s Goddard Space Flight Center, Greenbelt, Md., who authored the study.
Comiso used satellite data to track trends in minimum Arctic sea ice cover and temperature over the Arctic from 1978 to 2000. Since sea ice does not change uniformly in terms of time or space, Comiso sectioned off portions of the Arctic data and carefully analyzed these sections to determine when ice had reached the minimum for that area each year. The results were compiled to obtain overall annual values of perennial sea ice.
Prior to the complete data provided by satellites, most records came from sparsely located ocean buoys, weather stations, and research vessels.
The rate of decline is expected to accelerate due to positive feedback systems between the ice, oceans and atmosphere. As temperatures in the Arctic rise, the summer ice cover retreats, more solar heat gets absorbed by the ocean, and more ice gets melted by a warmer upper water layer. Warmer water may delay freezing in the fall, leading to a thinner ice cover in the winter and spring, which makes the sea ice more vulnerable to melting in the subsequent summer.
Also, the rise in summer ice temperatures by about 1.2 degrees Celsius (2.2 Fahrenheit) each decade could lengthen the summers, allowing earlier spring thaws and later freeze dates in the fall, causing further thinning and retreat of perennial ice.
Comparing the differences between Arctic sea ice data from 1979 to 1989 and data from 1990 to 2000, Comiso found the biggest melting occurred in the western area (Beaufort and Chukchi Seas) while considerable losses were also apparent in the eastern region (Siberian, Laptev and Kara Seas). Also, perennial ice actually advanced in relatively small areas near Greenland.
In the short term, reduced ice cover would open shipping lanes through the Arctic. Also, massive melts could increase biological productivity, since melt water floats and provides a stable layer conducive to plankton blooms.
Also, both regional and global climate would be impacted, since summer sea ice currently reflects sunlight out to space, cooling the planet’s surface, and warming the atmosphere.
While the latest data came too late to be included in the paper, Comiso recently analyzed the ice cover data up to the present and discovered that this year’s perennial ice cover is the least extensive observed during the satellite era.
The study appears in the late October issue of Geophysical Research Letters, and was funded by NASA’s Cryospheric Sciences Program and the NASA Earth Science Enterprise/Earth Observing System Project.
The mission of NASA’s Earth Science Enterprise is to develop a scientific understanding of the Earth System and its response to natural or human-induced changes to enable improved prediction capability for climate, weather and natural hazards.
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Contact:
Krishna Ramanujan
Goddard Space Flight Center
Greenbelt, Md. 20771
(301) 286-3026
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January 1, 1990
January 1, 1999
Decadal Decline
These two images show Arctic sea ice extent from January 1, 1990, and January 1, 1999, respectively. These images were created using data from the Defense Meteorlogical Satellite Program’s (DMSP) Special Scanning Microwave Imager (SSM/I). Credit: NASA
Perennial Ice
Title for Fig. A: Average Perennial Ice Concentrations from 1979 to 1989
Credit: J.C. Comiso, NASA/GSFC and Rob Gersten, SSAI
Caption: This figure represents the average concentration of Arctic perennial ice cover using data derived for each year from 1979 to 1989. Perennial sea ice floats in the polar oceans and remains at the end of the summer, when the ice cover is at its minimum and seasonal sea ice has melted. This year-round ice averages about 3 meters (9.8 feet) in depth, but can be as thick as 7 meters (23 feet). The color bar represents percentages of sea ice within each satellite grid.
Title for Fig. B: Average Perennial Ice Concentrations from 1990 to 2000
Credit: J.C. Comiso, NASA/GSFC and Rob Gersten, SSAI
Caption: This graphic shows the average concentration of Arctic perennial ice cover for each year from 1990 to 2000.
Title for Fig. C: The Difference in Sea Ice Concentrations
Credit: J.C. Comiso, NASA/GSFC and Rob Gersten, SSAI
Caption: This image represents the difference in sea ice concentrations between the first 11 years (1979 to 1989) and the second 11 years (1990 to 2000) of perennial ice cover data. The color bar shows the difference in percentages from the earlier period to the latter. The biggest decline occurred in the western area (Beaufort and Chukchi Seas) while considerable losses were also apparent in the eastern region (Siberian, Laptev and Kara Seas). Also, the perennial ice actually advanced in relatively small areas, especially near Greenland.
Title for Fig. D: Projection for the Perennial Ice Cover in 2050
Credit: J.C. Comiso, NASA/GSFC and Rob Gersten, SSAI
Caption: This image represents the decadal average of the concentration of the perennial ice cover during the 2050s as projected from the current data set. This map was developed assuming a linear decline following the decadal change from the 1980s to the 1990s. Credit: NASA
Albedo
Ice reflects light from the sun. As polar ice caps melt, less sunlight gets reflected into space. It is instead absorbed into the oceans and land, raising the overall temperature, and fueling further melting. Credit: NASA
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