Forecasters hedge bets on extent of Arctic ice melt this summer

MARGARET MUNRO
Canwest News Service

Despite a big spring dip in the amount of Arctic sea ice, several leading forecasters do not expect a record-setting melt this summer.

An ice outlook, issued this week by 16 teams including one from the Canadian Ice Service, predicts there will be “modest” change comparable to the last two years. Fourteen of the 16 teams predict this year’s melt to be less than the extraordinary ice retreat seen in 2007.

But they also stress that the ice, which has adorned the top of the planet for hundreds of thousands of years, continues to melt away.

All the 2010 forecasts call for this year’s ice melt to be “well below” the 1979–2007 average.

The “overall trend” is toward “long-term loss of summer Arctic sea ice,” says the outlook, released by the Arctic Research Consortium of the U.S.

It publishes the outlook each spring as part of an international effort to share and improve forecasts about the constantly shifting polar ice.

Some of the ice-watchers argue more ice could survive the summer melt than in recent years because there is evidence of a “buildup of multi-year sea ice and a more stable ice pack.”

Others say the ice may approach a record-low minimum because of a “below-normal sea ice thickness overall, the thinning of sea ice in coastal seas, rotting of old multi-year sea ice, warm temperatures in April and May 2010, and the rapid loss of sea ice area seen during May.”

The Canadian Ice Service predicts 4.9 million square kilometres of ice will make it through the melt season. That is slightly more than the amount left in 2008, but would still be the third lowest in the last 30 years.

University of Alaska Fairbanks forecasters expect to see the most ice left — 5.7 million square kilometres — while a Russian group and the U.S. National Snow and Ice Data Centre have pegged 5.5 million square kilometres of ice as the minimum for this year.

Academic teams from the U.S. and Germany forecast this year’s melt could approach the stunning retreat that occurred in 2007, when ice shrank to 4.28 million square kilometres. That was the lowest levels since satellite measurements began in 1979 and 39 per cent below the long-term average.

While some researchers have suggested that the ice could soon melt away almost completely in the summer as a result of climate change, others say the more likely scenario is that the ice will slowly decline, with big melts some years and rebounds in others.

Part of the problem with ice forecasting is that it is largely based on data from satellites. They are good at measuring how large an area is covered by ice, but tell little about its thickness, says geophysicist Christian Haas, of the University of Alberta.

He says the limited available data make it difficult to predict what will happen this summer.

In April, there was plenty of ice in the Arctic, but much of it was so thin and fragile that it retreated at a record pace in May’s unusually warm weather. Several of the forecast teams say it is difficult to know how much of the remaining ice is thick and solid enough to withstand the summer heat.