The speech by former US Vice-President Al Gore was apocalyptic. ‘The North Polar ice cap is falling off a cliff,’ he said. ‘It could be completely gone in summer in as little as seven years. Seven years from now.’

Those comments came in 2007 as Mr Gore accepted the Nobel Peace Prize for his campaigning on climate change.

But seven years after his warning, The Mail on Sunday can reveal that, far from vanishing, the Arctic ice cap has expanded for the second year in succession – with a surge, depending on how you measure it, of between 43 and 63 per cent since 2012.

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.