The National Snow and Ice Data Center said on its website that the ice has melted beyond the 2005 minimum of 5.32 million square kilometers (2.05 million square miles). The figure arouses particular concern, as this summer has been comparatively cold, suggesting that the shrinking of the ice is gathering momentum.
The center said that "through the beginning of the melt season in May until early August, daily ice extent for 2008 closely tracked the values for 2005," but that the swift decline has continued through August, unlike in 2005.
Scientists say that the melting season ends in a few weeks, and then it will be possible to say for certain whether a new record low has been reached.
In 2007 the Arctic ice melted to about 4.3 million square kilometers (1.7 million square miles).
The melting icecap is a key piece in the global climate jigsaw. As the ice cover shrinks, the region's albedo - its ability to reflect sunlight back into the atmosphere - declines, and more heat is absorbed by the dark water surface, causing further warming, in what scientists call a positive feedback process.