The eruption of Mt. Pinatubo in June 1991 was the largest in the twentieth century. One of its effects was to produce cooler and drier conditions in the years following the eruption. We present the results of an integrated model study of the effect of these climatic changes on the emissions of isoprene from the biosphere. Our emissions model simulations showed that global isoprene emissions were reduced by 9% from 1990 to 1992. When incorporated into our model of global atmospheric chemistry this reduction of isoprene emissions led to an increase in the tropospheric OH burden of 2%. This caused an increase in the removal of methane via oxidation by OH of up to 5 Tg per year. This could have contributed to the observed changes in methane growth rate at this time.