A record quantity of northern polar ice was lost this year, according to scientists who presented their findings at a conference of the American Geophysical Union held this weekend in San Francisco. Surface melt in Greenland, for example, was the highest in recorded history, and extended to previously unaffected altitudes. In total, there were about 265,000 square miles of melt on the Greenland ice sheet this year, more than double that of 10 years ago. Although the scientists acknowledged that natural variations could account for some of the accelerated melting, they noted that glacial and sea ice melt, disappearing permafrost, the northward creep of vegetation, and increased fresh-water runoff together make “a compelling case that something is going on,” according to Larry Hinzman of the University of Alaska at Fairbanks. That “something” would be human influences on the atmosphere, including ozone depletion and global warming from greenhouse gas emissions. Changes in sea-ice levels have potentially dramatic implications for the global climate, because, while sea ice reflects 80 percent of solar radiation, melted sea ice — water — reflects just 20 percent, creating a positive feedback loop for further warming.