Solution:Estimates of relative contributions to additional greenhouse forcing during particular periods do not fully take into account differences in atmospheric residence times among the important greenhouse gases. Here we extend recent work on halocarbons 5. 6 by proposing an index of global warming potential for methane, carbon monoxide, nitrous oxide and CFCs relative to that of carbon dioxide.We find, for example, that methane has, per mole, a global warming potential 3.7 times that of carbon dioxide. On this basis, carbon dioxide emissions account for 80% of the contribution to global warming of current greenhouse gas emissions, as compared with 57% of the increase in radiative forcing for the 1980s.