COULD REDUCING FOSSIL-FUEL EMISSIONS CAUSE GLOBAL WARMING

WHEN fossil fuel is burned, both carbon dioxide and sulphur dioxide are added to the atmosphere. The former should cause warming of the lower atmosphere by enhancing the greenhouse effect, whereas the latter, by producing sulphate aerosols, may cause a cooling effect. The possibility that these two processes could offset each other was suggested many years ago (see, for example, ref. 1), but during most of the intervening period, attention has focused on the greenhouse effect. Interest in tropospheric aerosols has, however, recently been rekindled by the realization that they may influence climate, not only through clear-sky radiative effects 2-5, but also by modifying cloud albedo 6-8. Here I examine the sensitivity of the climate system to simultaneous changes in SO2 and CO2 emissions, as might occur if controls were imposed on fossil-fuel use. Over the next 10-30 years, it is conceivable that the increased radiative forcing due to SO2 concentration changes could more than offset reductions in radiative forcing due to reduced CO2 emissions.