Monday, July 30, 2012

Surface Ice Melt in Greenland

It has been an extraordinary month of ice melt on the ice sheet in Greenland, with 97 percent of the ice surface area melting on July 12, and melting continuing over a wide area until July 22. Sitting two miles above sea level, the ice surface at the top of Greenland remains frozen almost all the time, with the last large-scale melt occurring in 1889.

The standard climate models assume this state of things will continue, and until recently it was assumed that it would take at least until 3400 for the ice sheet to melt away from below. If weather becomes more variable so that spring-like surface melt events occur in summer, surface melt could become a significant part of the disappearance of the Greenland ice sheet.

Melting on the Greenland ice sheet creates less than 1 millimeter of sea-level rise per year. This month’s surface melt could have added an extra 0.1 millimeter to sea levels. This is not alarming in itself, but could become a problem if it repeats — every millimeter of sea level rise translates to more areas subject to street flooding in coastal towns. The top of Greenland is not cooling off quickly, though. The conditions there currently are barely below freezing (–3°C) and foggy, indicating more melting is occurring (though surely not at a significant pace).

Jeff Masters comments on the weather data:

More context and the month in infrared (surface temperature) satellite images at