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Around 250 million years ago life on earth nearly perished.In the great extinction at the end of the Permian era life was reduced to 5-10% of previous species diversity. Why should this ancient mass extinction be of any interest to us today? Because that great dying resulted from processes which saw, over 10 000 years, an increase in average world temperature of 5-7 degrees Celsius turning the planet into a "post-apocalyptic greenhouse". Our world is warming, and according to the 2007 IPCC report it is "at least a nine out of ten chance" that this warming is anthropogenic - that is to say, caused by human activities. And it is warming at a rate far beyond that reflected in the 10 000 year period that saw off most of life on earth. The IPCC report says we are looking at a 2-4.5 degree increase over the next hundred years.This is frightening enough, particularly as the report took a conservative approach to the positive feedback mechanisms which might kick in and drive the temperature increase beyond that that almost extinguished all life on earth. More recent work from NASA's Goddard Institute for Space Studies, that takes these feedback mechanisms into consideration, suggests that we may reach, in the next 100 years, a point - an "albedo flip" - at which time talk of average world temperature increasing 2-3 degrees C will be seen as wildly optimistic and wrong. |
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