The general trend of recent news and data around the melting of the polar ice caps is not a good one. In fact, the recent data shows that the thinning and melting of the western Arctic sea ice in particular is progressing more than 3 times faster than even the most pessimistic of climate models projected. According to William Chapman, et. al. at the University of Illinois, this melting is progressing so swiftly now, that:
Today [August 9, 2007], the Northern Hemisphere sea ice area broke the record for the lowest ice area in recorded history. The new record came a full month before the historic summer minimum typically occurs. There is still a month or more of melt likely this year. It is therefore almost certain that the previous 2005 record will be annihilated by the final 2007 annual minima closer to the end of this summer.
Hansen warns (read Hansen’s full article on Sea Level Rises at New Scientist) that the likely results of ice faster-than-expected melts are huge rises in Sea levels. Hansen notes:
“Sea level is already rising at a moderate rate. In the past decade, it increased by 3 centimetres, about double the average rate during the preceding century. The rate of sea level rise over the 20th century was itself probably greater than the rate in the prior millennium, and this is due at least in part to human activity.”
Worse yet, is the very real possibility of runaway collapse.
“..the primary issue is whether global warming will reach a level such that ice sheets begin to disintegrate in a rapid, non-linear fashion on West Antarctica, Greenland or both. Once well under way, such a collapse might be impossible to stop, because there are multiple positive feedbacks. In that event, a sea level rise of several metres at least would be expected.
As an example, let us say that ice sheet melting adds 1 centimetre to sea level for the decade 2005 to 2015, and that this doubles each decade until the West Antarctic ice sheet is largely depleted. This would yield a rise in sea level of more than 5 metres by 2095.”
Hansen seems convinced that the most recent data on historical temperatures is more accurate than earlier research, and places our current global temperature within 1 degree of its highest temperature in the past million years, making the horrific prospect of a 5 meter increase in sea levels seem much more ominous.
“The broader picture strongly indicates that ice sheets will respond in a non-linear fashion to global warming – and are already beginning to do so. There is enough information now, in my opinion, to make it a near certainty that business-as-usual scenarios will lead to disastrous multi-metre sea level rise on the century time scale.”