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Some regions of Arctic sea ice are thinning up to twice as fast as previously thought, according to measurements that account for how climate change is affecting snow.

For decades, rising global temperatures have been causing a decline in sea ice extent, which is closely and accurately mapped. But there is far greater uncertainty about the thickness of the ice, which is a crucial figure to understand because thinner ice is more prone to melt in summer.

Typically, we have estimated the thickness of sea ice by measuring the height of its surface above sea level, and then taking into account that this height is lower than it should be because thick snow resting on top of the ice weighs it down.

But at University College London says the approach isn鈥檛 good enough because it relies on maps of snow depth from 1999 that were still being used, despite the fact we know that the snow has become shallower in the two decades since because of climate change.

To narrow down the uncertainty, he and his colleagues combined radar data from satellites with a much more realistic estimate of the amount of snow on the sea ice.

Swapping the maps for modelling of snow levels, which was calibrated against real world observations, the sea ice thickness was found to be declining 60-100 per cent faster between 2002 and 2018. The year-to-year swings in thinning rates were also found to be much bigger than thought, up 76 per cent, than with the old method.

Having a more realistic handle on sea ice thinning will help build more accurate climate change models of the future, while understanding the annual variations will help the , says Mallett.

鈥淪ea ice thickness remains highly uncertain compared to the area that the sea ice covers. However, this paper is a significant advance in characterising the trends that we鈥檙e seeing in the thickness, and those are trends that reflect an Arctic warming at three times the global rate,鈥� says Mallett.

The findings only apply to four of the seven seas that surround the central Arctic, because satellite radar data for the central region only dates to 2010, and the ice at the centre tends to be thicker and survive for several years.

There are also what Mallet describes as 鈥渓arge uncertainties鈥� in how far satellite radar systems penetrate through the snow to the sea ice, and it is unclear exactly how much snow there is in the Arctic.

Peter Wadhams at the University of Cambridge says a 鈥済igantic hole鈥� in the research is that it omits reliable measurements of sea ice thickness taken by submarines up to 2007. Mallett says such readings were only taken at single 鈥減oints鈥�, and don鈥檛 necessarily represent the much larger areas of thousands of square kilometres that his team looked at.

Walt Meier at the US-based National Snow and Ice Data Center says the new approach is a big improvement on the old one. 鈥淭he method uses a sophisticated snow model that allows snowfall to be tracked, wind to blow snow on the ground, and it moves the snow on the ice as the ice drifts with winds and currents,鈥� he says.

The decline of Arctic sea ice shows no sign of letting up this year, with its extent than when the region set a record-breaking summer minimum in 2012. The ice usually reaches its minimum in September before refreezing for winter.