They show that an ice cover began to form there far earlier, some 37 million years ago.

In July 2012, this melt zone covered 97 percent of the ice cover.

CryoSat will assess the state of the world's ice cover.

But now the ice cover had bounced back, proving how wrong they were.

The ice cover meant that natural light was not always strong enough for us to film.

Of the ice cover still present in 2000, 26% had disappeared by 2007.

They have tracked the ebb and growth of the ice cover for the past five years.

The increase in the lake's surface temperature may be related to the decreasing ice cover.

So most of the solar radiation that comes in and strikes the ice cover goes back to space.

This was done immediately after the ice cover melted on the sea.