Ice-free Arctic: Have we reached the tipping point?

Good BBC News story by Richard Black.

Nothing to worry about for the next five years, as long as you don't depend on anything or anyone located less than 22 feet above sea level.

A few years ago, scientists were predicting ice-free Arctic summers by about 2080. Then computer models started projecting earlier dates, around 2030 to 2050.

Then came the 2007 summer that saw Arctic sea ice shrink to the smallest extent ever recorded, down to 4.2 million sq km from 7.8 million sq km in 1980.

By the end of last year, one research group was forecasting ice-free summers by 2013

"I think we're going to beat last year's record melt, though I'd love to be wrong," said Dr Stroeve.

"If we do, then I don't think 2013 is far off anymore. If what we think is going to happen does happen, then it'll be within a decade anyway." ...

"This is a positive feedback process," commented Dr Ian Willis, from the Scott Polar Research Institute in Cambridge.

"Sea ice has a higher albedo (reflectivity) than ocean water; so as the ice melts, the water absorbs more of the Sun's energy and warms up more, and that in turn warms the atmosphere more - including the atmosphere over the Greenland ice sheet."

Greenland is already losing ice to the oceans, contributing to the gradual rise in sea levels. The ice cap holds enough water to lift sea levels globally by about 7m (22ft) if it all melted.