Arctic sea ice, which is frozen seawater floating on the ocean surface, may be thinning in coastal regions up to twice as fast as previously thought, scientists believe.

The findings, published in the journal Cryosphere, raise fresh concerns that some parts of the Arctic could become ice-free by 2040, with potentially devastating consequences.

The Arctic, together with the Antarctic, act as the world's refrigerator, with white snow and ice in the region reflecting heat back into space, while other parts of the planet continue to absorb heat.

Loss of ice in these regions would not only cause global temperatures to rise, but would also increase the risk of extreme weather and flooding in many coastal regions around the world.

Researchers from University College London (UCL), who led the modelling study, said the thinning of sea ice in the coastal Arctic seas also has implications for human activity in the region - both in terms of shipping along the Northern Sea Route as well as the extraction of resources from the sea floor, such as oil, gas and minerals.

Robbie Mallett, a PhD student at UCL Earth Sciences, and the study's lead author, said: "More ships following the route around Siberia would reduce the fuel and carbon emissions necessary to move goods around the world, particularly between China and Europe.

"However, it also raises the risk of fuel spillages in the Arctic, the consequences of which could be dire.

"The thinning of coastal sea ice is also worrying for indigenous communities, as it leaves settlements on the coast increasingly exposed to strong weather and wave action from the emerging ocean."

As part of their study, the experts looked at data from the European Space Agency's (ESA) CryoSat-2 satellite to calculate sea ice thickness.

The team also used a new snow model, dubbed SnowModel-LG, to calculate snow depth and density in the coastal regions of the Arctic.

Mr Mallett said: "Previous calculations of sea ice thickness are based on a snow map last updated 20 years ago.

"Because sea ice has begun forming later and later in the year, the snow on top has less time to accumulate.

"Our calculations account for this declining snow depth for the first time, and suggest the sea ice is thinning faster than we thought."

They researchers found that the rate of sea ice decline in the coastal regions of the Arctic was 70% to 100% faster than previously thought.

In the three coastal seas of Laptev, Kara and Chukchi, waters increased by 70%, 98% and 110% respectively, when compared with earlier calculations, the team said.

And across all seven coastal seas, the variability in sea ice thickness from year to year increased by 58%, they added.

Study co-author Professor Julienne Stroeve, of UCL Earth Sciences, said: "There are a number of uncertainties in measuring sea ice thickness, but we believe our new calculations are a major step forward in terms of more accurately interpreting the data we have from satellites.

"We hope this work can be used to better assess the performance of climate models that forecast the effects of long-term climate change in the Arctic - a region that is warming at three times the global rate, and whose millions of square kilometres of ice are essential for keeping the planet cool."