Scientists in the US have presented dramatic forecasts for the disappearance of Arctic sea ice. Modelling studies presented at an American Geophysical Union meeting indicate that ithe northern polar waters could be ice-free in summers as early as 2013

Summer melting this year reduced the ice cover to 4.13 million sq km, the smallest ever extent in modern times. But this low point was not even incorporated into the model runs of Professor Maslowski and his team at the Naval Postgraduate School, Monterey, California. The figures used data sets from 1979 to 2004. Other teams have variously produced dates for an open summer ocean anywhere between about 2040 to 2100. But Maslowski believes these models have seriously underestimated some key melting processes.

The Intergovernmental Panel on Climate Change (IPCC), the UN-led body which assesses the state of the Earth's climate system, uses an averaged group of models to forecast ice loss in the Arctic. But it is has become apparent in recent years that the real, observed rate of summer ice melting is now starting to run well ahead of the models. The minimum ice extent reached in September 2007 was much lower than the previous record for ice withdrawal set in 2005, of 5.32 million square km. This compares with an average minimum, based on data from 1979 to 2000, of 6.74 million square km.

Professor Peter Wadhams from Cambridge University, UK, is an expert on Arctic ice. He has used sonar data collected by Royal Navy submarines to show that the volume loss is outstripping even area withdrawal, which is in agreement with the model result of Professor Maslowski. "Some models have not been taking proper account of the physical processes that go on," he commented. "The ice is thinning faster than it is shrinking; and some modellers have been assuming the ice was a rather thick slab. Wieslaw's model is more efficient because it works with data and it takes account of processes that happen internally in the ice. The loss this year will precondition the ice for the same thing to happen again next year, only worse. There will be even more opening up, even more absorption and even more melting. "In the end, it will just melt away quite suddenly. It might not be as early as 2013 but it will be soon, much earlier than 2040."

The US National Snow and Ice Data Center (NSIDC) collects the observational data on the extent of Arctic sea ice, delivering regular status bulletins. Its research scientist Dr Mark Serreze was asked to give one of the main lectures here at this year's AGU Fall Meeting. Discussing the possibility for an open Arctic ocean in summer months, he told the meeting: "A few years ago even I was thinking 2050, 2070, out beyond the year 2100, because that's what our models were telling us. But as we've seen, the models aren't fast enough right now; we are losing ice at a much more rapid rate. My thinking on this is that 2030 is not an unreasonable date to be thinking of, and yet Dr Maslowski has the view that it may be as early as 2013. He's on the record now. We'll see how that pans out."