Arctic Defrost?

This September, the NSIDC (the US National Snow and Ice Data Center) revealed that the extent of the September sea ice in the Arctic this year was at the lowest point since measurements started in 1979 (a link to the press release can be found here). 

An image of the extent of sea ice in September 2012. The pink line is the average extent around this time over the period of 1979-2000 (NSIDC)

The record is in line with observations over the last decades, showing that there has been a steady decline in summer sea ice extent. Scientists believe that this trend is largely due to higher temperatures as a result of global warming.

A graph comparing sea ice extent between 2012, 2007 (the previous record-low) and the 1979-2000 average (from 30 October 2012 - NSIDC website)

Another observation is the decrease in thickness of the ice. The ocean water absorbs more heat, and slowly releases it when the sun sets - making it more difficult for the ice to regrow. Most of the ice is now only 1 or 2 years old, and is more susceptible to melting. Moreover, the disappearance of the ice means that less sunlight can be reflected back, resulting in warmer conditions. The positive albedo effect is working here as well.

It was previously thought from models from the IPCC report from 2007 that the Arctic might become ice free in summers by 2100. However, these recent data seem to indicate that the decline in ice is progressing faster than previously thought. Scientists now believe that summer ice might disappear completely from the Arctic region in a few decades.

I want to conclude this short update on the state of the Arctic sea ice with an informative clip from Climate Watch Magazine, where the sea ice has been animated based on the observations from 1979 onwards. It also shows the age of the ice in different colours - note how the 1 year old ice starts to dominate towards the end. It can be found here (I'd insert it - but it's a bit too big!).

In a following post, I'll give more attention to albedo feedback and ice, and I'll also discuss the effect of soot on ice reflectivity, something that's become more important in recent years.