CLIMATE CHANGE AND ISOPRENE EMISSIONS FROM VEGETATION

A global model was developed for estimating spatial and temporal patterns in the emission of isoprene from vegetation under the current climate. Results were then used to evaluate potential emissions under doubled-CO2 climate scenarios. Current emissions were estimated on the basis of vegetation type, foliar biomass (derived from the satellite-generated Global Vegetation index), and global databases for air temperature and photoperiod. The model had a monthly time step and the spatial resolution was 0.5 degrees latitude and longitude. Emissions under patterns of precipitation and temperature projected for a doubling of atmospheric CO2 were estimated based on predicted changes in the areal extent of different vegetation types, each having a specific rate of annual isoprene emissions. The global total for current emissions was 285 Tg. The calculated isoprene emissions under a doubled-CO2 climate were about 25% higher than current emissions due mainly to the expansion of tropical humid forests which had the highest annual emission rates. An increase in isoprene emissions would be likely to increase atmospheric concentrations of ozone and methane, which are important greenhouse gases, and thus act as a positive feedback to global warming. Detailed treatment of this question, however, will require incorporation of these emission surfaces into global atmospheric chemistry models.