Arctic sea ice smallest since records began

Scientists from the University of Colorado’s Cooperative Institute for Research in Environmental Sciences (CIRES) found that in September this year, the extent of Arctic sea ice – the area of the ocean where sea ice exceeds 15% coverage – was down 4% on any previous September since satellite monitoring began in 1978. The total area of ice floes was 6% lower.

“We had a hunch it was setting up to be a record year in August,” said Ted Scambos of NSIDC, who has been working in the polar regions. “What we saw really surprised us.” Not only was the sea ice retreating in nearly every area, but it was also unusually thin, he explained.

This year’s record is part of a trend, said CIRES climatologist Konrad Steffen. His analysis shows a considerably higher melting trend since 1979, with the melt area increasing on average by 16%. This has been interrupted once – in 1992, when Mount Pinatubo in the Philippines erupted. The melt area in summer 2002 was 2.6 times that in 1992. Other extreme melt years were 1991 and 1995.

“We actually have some century-long records from the region around Iceland – based mostly on ship and land reports,” Mark Serreze, lead author of the paper, told edie. “These show evidence of a long-term decline in sea ice for that region.”

The rise in temperature is attributable in part to the atmospheric circulation through the Arctic Oscillation. This varies between two states: positive and negative. During the AO positive state, winds are stronger and temperatures warmer over the Arctic and sub-arctic. This also results in wetter weather in Alaska, the UK and Scandinavia, and drier conditions in the US and the Mediterranean.

The negative phase of the AO consists of higher pressure over the Arctic, lighter winds and colder temperatures. This also results in higher temperatures in the US east of the Rocky Mountains and in the UK.

The AO was fluctuating between the positive and negative states for most of the 20th century. However, since the mid 1980s the positive state has been increasingly dominant, according to the US-based National Snow and Ice Data Center. Recent research has suggested that the trend may be related to the destruction of the ozone layer, says the NSIDC.

Despite recent reports that the ozone layer is recovering (see related story), the warmer trend could still continue, says Serreze. “The most recent thinking is that the AO may re responding more strongly to changes in carbon dioxide – and other greenhouse gases – through its impact on the stratosphere.” Carbon dioxide concentrations are expected to continue to rise, he says.

On the other hand, says Serreze, the winter trend of AO’s ‘brother’, the North Atlantic Oscillation (NAO), is related to changes in sea surface temperatures over the tropical Indian Ocean.

It is likely that the amount of sea ice at the Arctic will continue to decline over this century, said Serreze. “With these trends, we may see an approximate 20% reduction in the annual mean sea ice by 2050, and by then we might be approaching no ice at all during the summer months.”

NASA has also recently claimed that if the current melting rates in the Arctic continue for a few more decades, the perennial sea ice will disappear entirely within this century.