Greenland's massive ice sheet is melting rapidly, losing the equivalent of Lake Houston every six hours. That's the conclusion of a study by University of Texas at Austin scientists that appears to confirm earlier, controversial research that suggests the melting of Greenland's ice has nearly tripled since the late 1990s. Greenland's ice sheet contains about 10 percent of the world's fresh water. The findings concern climate scientists, who say that since the Industrial Revolution, and especially since the mid-1900s, carbon dioxide levels have risen by more than 40 percent. They attribute much of the increase to fossil fuel burning and...