The images were released less than a week after a paper, published in the U.S. journal Science, found that year-round sea ice in the Arctic shrank by one seventh between 2004 and 2005.
Loss of sea ice does not affect global sea levels. Ice that floats in the water displaces its own volume.
However ice that is on land, as an icesheet, glacier or permanent snowcap, adds to sea level when it melts and runs off.
Retreating ice cover also creates a vicious circle, adding to the warming caused by greenhouse gases — carbon emissions, mainly from fossil fuels, that trap the sun's heat.
Ice, being white, reflects the sun's rays. Less ice therefore means the sea warms, which in turn accelerates the shrinkage.
The shrinkage of the Arctic icecap is viewed with alarm by scientists, as it appears to perturb important ocean currents elsewhere, notably the Gulf Stream, which gives western Europe its balmy climate.
It also threatens animals such as polar bears and seals that depend on ice.
There are geopolitical implications, too, as Canada, Russia and the United States jockey to claim rights over transpolar passages that open up within their newly ice-free waters.
