Runaway Warming

The extent of Arctic sea ice undulates like a yearly sine wave—rising in October, peaking in winter, and melting all spring and summer. This September we are likely to observe the lowest of lows; Greg Laden writes “There is less sea ice in the Arctic Circle than recorded in recent history.” More ice has also melted in Greenland this season, with 4 weeks still to go. Greg says, “glacial melting is both more important than one might think and also more complicated.” For example, the albedo of Greenland’s ice sheet (the proportion of sunlight reflected back into the atmosphere) varies depending on the snowpack. “The white fresh frozen snow that falls over the winter is highly reflective,” but “as it melts and gets slushy and mixes with water is has lower albedo.” This is an example of a feedback mechanism, as warmth and melting allows more sunlight into the ice. Additional feedback could occur as methane, a potent greenhouse gas, is freed from polar ice sheets.