Arctic sea ice melted to its second-lowest level since measurements began in 1979, the Colorado- based National Snow and Ice Data Center said Thursday. 

The ice coverage of 4.67 million square kilometres had only recovered slightly from the 2007 record low of 4.28 million square kilometres, the centre said. 

The most recent satellite measurement, taken on September 14, the annual lowest point in the cycle of melt and growth, reinforced the 30-year downward trend in Arctic ice cover, the center said. 

When compared to the long-term average from 1979 to 2000, the 2008 figure was 34 per cent lower than that average. 

"Both within and beyond the Arctic, the implications of the decline are enormous," said NSIDC senior scientist Mark Serreze. "When you look at the sharp decline that weve seen over the past thirty years, a 'recovery' from lowest to second lowest is no recovery at all." 

In June, Serreze warned that there was a 50-50 chance that the North Pole would melt entirely this summer. 

Arctic ice historically reaches its thinnest point in September after the long, bright summer. The ice is thickest in March. 

After last year's record melt, the so-called Northwest Passage was briefly ice-free by September 2007. New ice built up during the cold winter, but one-year ice is more susceptible to melting than century- old ice masses, Serreze noted. 

The data strengthens growing concern about the rapid pace of global warming blamed on carbon emissions from burning fossil fuels. 

The center said that summer ice losses allowed solar energy to warm up the oceans mroe than ever. Since the waer stores heat longer than air, the melt continues long after the sun begins to wane in Arctic latitudes.