To put it another way, an area the size of Alaska, America’s biggest state, was open water two years ago, but is again now covered by ice.
The most widely used measurements of Arctic ice extent are the daily satellite readings issued by the US National Snow and Ice Data Center, which is co-funded by Nasa. These reveal that – while the long-term trend still shows a decline – last Monday, August 25, the area of the Arctic Ocean with at least 15 per cent ice cover was 5.62 million square kilometres.
This was the highest level recorded on that date since 2006 (see graph, right), and represents an increase of 1.71 million square kilometres over the past two years – an impressive 43 per cent.
Other figures from the Danish Meteorological Institute suggest that the growth has been even more dramatic. Using a different measure, the area with at least 30 per cent ice cover, these reveal a 63 per cent rise – from 2.7 million to 4.4 million square kilometres.