Satellite imagery (European Space Agency's CryoSat 2) has confirmed the prediction of computer modeling that the total volume of Arctic sea ice is declining rapidly. The total volume is now one-fifth of the 1980 level. If the trend continues the Arctic will be ice free in summer within the decade which will result in more rapid global warming with characteristic extreme, prolonged weather events.
credit: Stroeve et al
The area of ice cover has been shrinking over the last decade too, reaching a record minimum in September 2012, but the volume decease is more troubling since it indicates sea ice is becoming progressively thiner more rapidly than previously thought. Warmer arctic temperatures also mean vast areas of permafrost will begin thawing thereby releasing even more carbon to the atmosphere. This amplification loop will intensify the effects of global warming including significantly raising sea levels. If the ice sheet on Greenland melts--and many climate scientists think it will--sea levels will rise twenty feet or enough to flood lower Manhattan, all of New Orleans, and other coastal population centers worldwide. Greenland is at a tipping point now with surface melting at the highest elevations and in record extent:
credit: J.E. Box et al
melt index = the number of days melting occurred x area melting occurred