Arctic sea ice may vanish this century

By CAT LAZAROFF

WASHINGTON, DC - (ENS) - Perennial sea ice - the floating ice that remains year round near the Arctic Circle - could vanish entirely by the end of this century, warns a new study by researchers at the National Aeronautics and Space Administration. The NASA study concludes that sea ice is now melting about nine per cent faster than prior research had indicated, due to rising temperatures and interactions between ice, ocean and the atmosphere.

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 three metres in depth, but can be as thick as seven metres.

But if current melting rates continue, by the year 2099, there may be no sea ice left in the Arctic. Melting sea ice would not affect sea levels, but it could have an impact on summer shipping lanes, plankton blooms, ocean circulation systems, and the 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 Centre 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 analysed these sections to determine when ice had reached the minimum for that area each year.

Prior to the complete data provided by satellites, most records came from sparsely located ocean buoys, weather stations, and research vessels. Comiso compiled all available data to obtain overall annual values of perennial sea 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 - the Beaufort and Chukchi Seas - while considerable losses were also apparent in the eastern region of the Siberian, Laptev and Kara Seas. In small areas near Greenland, perennial sea ice advanced a bit, Comiso found.

The rate of decline is expected to accelerate due to interactions 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 autumn, leading to a thinner ice cover in the winter and spring, which makes the sea ice more vulnerable to melting in the subsequent summer.

The study found that temperatures in the Arctic are increasing at the rate of 1.2 degrees Celsius per decade. This rise in summer ice temperatures could lengthen the summers, allowing earlier spring thaws and later freeze dates in the fall, causing further thinning and retreat of perennial ice.

In the short term, reduced ice cover would open shipping lanes through the Arctic. Massive melts could also increase biological productivity, since melt water floats and provides a stable layer conducive to plankton blooms.

Shrinking sea ice also affects Arctic wildlife like polar bears and seals, which depend on both seasonal and perennial ice.

"Since the sea ice is melting earlier in the spring, polar bears move to land earlier without having developed as much fat reserves to survive the ice free season," explained Lynn Rosentrater, a climate scientist at the World Wildlife Fund's Arctic programme. "They are skinny bears by the end of summer, which in the worst case can affect their ability to reproduce."

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. As the ice expanse shrinks, less sunlight will be reflected, allowing the sun to warm more of the ocean.

While the latest data came too late to be included in the paper, Comiso recently analysed the ice cover data up to the present and discovered that this year's perennial ice cover is the least extensive observed during the era of satellite data.

Previous studies have shown that sea ice in the Arctic Circle is melting at a rate of 37,000 square kilometres per year; the new NASA study suggests the current melt rate may be even faster.

The mechanisms behind the loss or gain of sea ice are still uncertain. Earlier this year, researcher Claire Parkinson of the Goddard Space Flight Center noted that the ice cover around Antarctica has increased since the late 1970s, at the same time that Arctic sea ice has declined.

In a study published in the "Annals of Glaciology," Parkinson found that average southern ice seasons have lengthened, with perennial ice growing and seasonal ice persisting for longer periods. Parkinson's research found longer ice seasons in the Ross Sea, but in other Antarctic waters, including most of the Amundsen Sea and almost the entire Bellingshausen Sea, sea ice seasons are getting shorter.

The Antarctic changes appear to be linked to regional temperature changes - warming seas and surface temperatures were linked to shrinking ice. The same appears to be true in the Arctic, but the feedback links between ice and ocean and atmosphere make the total picture more complicated, Comiso said.

The new NASA study appears in the late October issue of the journal "Geophysical Research Letters," and was funded by NASA's Cryospheric Sciences Program and the NASA Earth Science Enterprise/Earth Observing System Project.

Herald feature: Environment