For the second year in a row, the fabled Northwest Passage has opened in the Arctic—thanks to a sea-ice melt that has already shrunk the polar cap to the second smallest extent ever recorded. And with a few more weeks to go in the summer thaw season, 2008 could surpass 2007 as the smallest amount of sea ice on record, according to the National Snow and Ice Data Center (NSIDC).

This year's record-breaking melt was, to some extent, set up by the 2007 season—also a record-breaker. More open ocean means more trapped heat in the water, which means that thinner ice forms during the long Arctic winter. Thinner ice melts more readily when temperatures rise. So, despite a relatively cool summer this year, the sea ice is just melting away.

This has led some scientists to predict that the summer Arctic could be ice-free within a decade. But be careful what you wish for: Although that may open some shipping lanes and fishing grounds, it's bad news for polar bears and other Arctic sea life. As it stands, the sea ice needs to shrink by just 166,000 square miles (430,000 square kilometers) to surpass last year's record, after having already shrunk 760,000 square miles (two million square kilometers) below average.

And, according to NSIDC, this year's melt is continuing at a "brisk pace," unlike previous record years, which slowed by the end of August. That means by late September a new low in global warming annals may be reached.