Antarctica melting Climate change and the journey to the 'doomsday glacier'

The images are murky at first.

Sediment sweeps past the camera as Icefin, a bright yellow remotely operated robot submarine, moves tentatively forward under the ice.

Then the waters begin to clear.

Icefin is under almost half a mile (600m) of ice, at the front of one the fastest-changing large glaciers in the world.

Suddenly a shadow looms above, an overhanging cliff of dirt-encrusted ice.

It doesn't look like much, but this is a unique image - the first ever pictures from a frontier that is changing our world.

Icefin has reached the point at which the warm ocean water meets the wall of ice at the front of the mighty Thwaites glacier - the point where this vast body of ice begins to melt.

The 'doomsday' glacier
Glaciologists have described Thwaites as the "most important" glacier in the world, the "riskiest" glacier, even the "doomsday" glacier.

It is massive - roughly the size of Britain.

It already accounts for 4% of world sea level rise each year - a huge figure for a single glacier - and satellite data show that it is melting increasingly rapidly.

There is enough water locked up in it to raise world sea level by more than half a metre.