ppmv, 450 ppmv, etc.). This report concludes that, for a variety of conceptual and practical reasons, it is more effective to assess climate stabilization goals by using global mean temperature change as the primary metric. Global temperature change can in turn be linked both to concentrations of atmospheric carbon dioxide (Table 1) and to accumulated carbon emissions.
An important reason for using warming as a reference is that scientific research suggests that many key impacts can be quantified for given tem-
SUSTAINED WARMING COULD LEAD TO SEVERE IMPACTS
Widespread coastal flooding would be expected if warming of several degrees is sustained for millennia. Model studies suggest that a cumulative carbon emission of about 1,000 to 3,000 gigatonnes (billion metric tonnes carbon) implies warming levels above about 2ºC sustained for millennia. This could lead to eventual sea level rise on the order of 1 to 4 m due to thermal expansion of the oceans and to glacier and small ice cap loss alone. Melting of the Greenland ice sheet could contribute an additional 4 to 7.5 m over many thousands of years.