Removal of chlorofluorocarbons by increased mass exchange between the stratosphere and troposphere in a changing climate

Chlorofluorocarbons (CFCs), along with bromine compounds, have been unequiv ocally identified as being responsible for most of the anthropogenic destru ction of stratospheric ozone(1). With curbs on emissions of these substance s, the recovery of the ozone layer will depend on their removal from the at mosphere. As CFCs have no significant tropospheric removal process, but are rapidly photolysed above the lower stratosphere, the timescale for their r emoval is set mainly by the rate at which air is transported from the tropo sphere into the stratosphere(2). Using a global climate model we predict th at, in response to the projected changes in greenhouse-gas concentrations d uring the first half of the twenty-first century, this rate of mass exchang e will increase by 3% per decade. This increase is due to more vigorous ext ra-tropical planetary waves emanating from the troposphere. We estimate tha t this increase in mass exchange will accelerate the removal of CFCs to an extent that recovery to levels currently predicted for 2050 and 2080 will o ccur 5 and 10 years earlier, respectively.