By
Dr.James Hansen, (Head of NASA Goddard Institute for Space Studies)
With an Introduction by Prof. Ed Hill Director of NOCS
National Oceanography Centre, Southampton
February 6th 2008
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ABSTRACT
Paleoclimate data show that climate sensitivity is ~¾°C per W/m2 (3°C for doubled CO2) with only fast feedback processes included. Equilibrium sensitivity, including slower surface albedo feedbacks, is twice that large for the range of climate states between glacial conditions and ice-free Antarctica. Decreasing CO2 was the main cause of a cooling trend that began 50 million years ago, with large scale glaciation occurring when CO2 fell to ~400-500 ppm. Global warmings, spurred by amplifying feedbacks, tend to be rapid. If humanity wishes to preserve climate resembling that in which civilization developed, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to ~300-350 ppm. The largest uncertainty in the target arises from possible changes of non-CO2 forcings. An initial 350 ppm CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting agricultural and forestry practices that sequester carbon. Overshoot of the target CO2 must be brief to avoid seeding irreversible catastrophic effects.
Background on James Hansen from Wikipedia
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Video and web page created by Barry Marsh NOCS 14-02-2008