Sea-ice increase is 'just a respite'

The volume of sea ice floating in the Arctic Ocean increased by about 50 per cent in October compared to last year, which was one of the lowest on record.

Europe's CryoSat satellite, which is designed to monitor sea-ice thickness, measured about 9000cu km of sea ice compared to the 6000cu km seen in October last year.

Scientists said that the rebound probably marked a temporary respite for the polar region, which has seen dramatic and long-term changes in recent decades because of regional warming that has melted Arctic ice on both land and sea.

The extent of the surface area covered by sea ice - measured by a different satellite - also saw an increase on the previous year, however it was still the sixth lowest since satellite records began in 1979. The seven lowest recorded sea-ice extents have all occurred in the past seven years.

Sea ice naturally increases from about mid-September to March and then recedes again during the warmer summer months. However, measurements from satellites and nuclear-powered submarines all show a significant long-term average decline in volume and surface area extent over the past four decades.

Although there was a significant return of the sea ice in October compared to the previous October, it was still less than half the estimated volume of the same time period in the early 1980s, said Professor Andrew Shepherd from University College London.

"The 9000 cubic kilometres we measured in October is still very much smaller than the 20,000 cubic kilometres we estimate for the same time in the early 1980s. So today's minimum still ranks among the lowest for the past 30 years," Shepherd said. "We do see year-to-year variations in the sea ice due to changes in weather patterns."

The European Space Agency's Cryosat satellite found 90 per cent of the rebound was the result of sea ice that had survived the summer melt season, the so-called "multiyear" ice. Just 10 per cent was first-year ice.

It found that the multiyear ice, which is generally thicker than single-year ice, is now on average about 20 per cent or around 30cm thicker than the previous year.

An Arctic "report card" for 2013, presented to the American Geophysical Union last week, found the long-term trends in the polar region continued to show it is warming rapidly and as a result has experienced dramatic changes, such as decreased snow cover, melting permafrost and diminishing ice on land and sea.

- Independent