Land-Use Change and Ozone Deposition Effects on BVOC Emissions 1850-2000

Feedbacks from human land-use change via altered biogenic volatile organic compound (BVOC) emissions from vegetation and atmospheric deposition have so far been neglected in historical assessments of the short-lived climate forcers. BVOC emissions profoundly alter atmospheric chemical composition and play an important role in the carbon cycle. The near balancing of the counteracting BVOC emission drivers, CO2 inhibition versus the effects of temperature and CO2-fertilization, implies that land-use change plays the critical role in determining changes to BVOC emissions. Ozone deposition on vegetation suppresses CO2 uptake by the land carbon sink and therefore affects BVOC production. A photosynthesis-dependent BVOC emission model that includes isoprene and monoterpene and a semi-mechanistic ozone uptake model has been implemented into the land biophysics module of NASA GISS ModelE. A set-up based on 8 PFTs and modern day climate projects a global source strength of 300 TgC/yr for isoprene and 29TgC/yr for monoterpene. The isoprene model performs reasonably well against above canopy emission flux measurements across a range of ecosystems but does not capture the seasonality of fluxes from the tropical rainforest ecosystem effectively and the model fluxes are too low in Canadian summer boreal. We apply a new harmonized land-use dataset for the period 1850-2000 in coupled transient simulations to quantify the relative importance of the global change drivers on past BVOC emissions through industrialization and to assess the impacts on the short-lived climate forcers.