FIGURE Syn.1 Recent studies show that cumulative carbon dioxide emission is a useful metric for linking emissions to impacts. Error bars reflect uncertainty in carbon cycle and climate responses to carbon dioxide emissions due to observational constraints and the range of model results. Cumulative carbon emissions are in teratonnes of carbon (trillion metric tonnes or 1,000 gigatonnes).

FIGURE Syn.1 Recent studies show that cumulative carbon dioxide emission is a useful metric for linking emissions to impacts. Error bars reflect uncertainty in carbon cycle and climate responses to carbon dioxide emissions due to observational constraints and the range of model results. Cumulative carbon emissions are in teratonnes of carbon (trillion metric tonnes or 1,000 gigatonnes).

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-

BOX SYN-1

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.



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