The most expansive study yet is helping to clarify long-held uncertainties about polar ice. The melting of polar ice sheets has sped up since 1992, raising sea levels 0.43 inches—a fifth of their total rise since then. And while the melting ice sheets accounted for 10% of the sea level rise in the 1990s, the process now accounts for closer to 30%. Greenland has lost more permanent ice to melting than has Antarctica, the Wall Street Journal notes, thanks to warmer air and ocean currents.
"If you extrapolate these results, Greenland is going to be a serious contributor to global sea-level rise," says an expert. "Its contribution, relative to other sources, is becoming greater and greater." Ice loss there is now occurring nearly five times faster than it was in the mid-1990s. Scientists' difficult task is to measure "mass balance," the difference between a year's snowfall on the permanent ice sheets and the amount of ice that breaks or melts off. The latest study offers twice the accuracy of previous work. The role of man-made climate change in the melting remains unclear, but nature can't account for all of it, says a study author. He adds that while there's no "immediate threat" from rising sea levels, the study calls for further investigation. (Read more Arctic stories.)