THE ROLE OF REFRIGERANTS IN CLIMATE-CHANGE

The primary chemicals used as refrigerants, chlorofluorocarbons (CFCs), and the compounds being considered as their replacements (HCFCs and HFCs) have been intensely studied because of concerns about chlorine chemistry effects on stratospheric ozone. Increasing attention is being given to the potential contributions of these compounds to global warming. CFCs, HCFCs and HFCs absorb infra-red radiation and thus are greenhouse gases that can exert an additional radiative forcing that tends to warm the climate. The purpose of this paper is to describe the current understanding of the role of refrigerants in affecting climate. Increasing atmospheric concentrations of CFCs have accounted for about 24% of the direct increase in radiative forcing from greenhouse gases over the last decade. However, an observed decrease in stratospheric ozone, thought to be connected to increasing stratospheric chlorine from CFCs (and, to a lesser extent, from other man-made compounds containing chlorine and bromine), suggests a negative radiative forcing or cooling tendency over the last decade. This cooling tendency has strong latitudinal gradients, but is, when globally averaged, about comparable in magnitude and opposite in sign to the radiative forcing from CFCs over this period. On the other hand, the radiative influence on climate from the compounds being considered as replacements, because of their shorter atmospheric lifetimes, should generally be much smaller than the CFCs. However, the effects on ozone should also be much smaller from the replacement compounds and there should be less cancellation in the overall globally averaged influence on climate.