Global climate forcing driven by altered BVOC fluxes from 1990 to 2010 land cover change in maritime Southeast Asia

Over the period of 1990–2010, maritime Southeast Asia experienced large-scale land cover changes, including expansion of high-isoprene-emitting oil palm plantations and contraction of low-isoprene-emitting natural forests. The ModelE2-Yale Interactive terrestrial Biosphere global chemistry–climate model is used to quantify the atmospheric composition changes, and for the first time, the associated radiative forcing induced by the land-cover-change-driven biogenic volatile organic compound (BVOC) emission changes (inline-formula+6.5 TgC yinline-formula⁻¹ isoprene, inline-formula−0.5 TgC yinline-formula⁻¹ monoterpenes). Regionally, surface-level ozone concentrations largely decreased (inline-formula−3.8 to inline-formula+0.8 ppbv). The tropical land cover changes occurred in a region of strong convective transport, providing a mechanism for the BVOC perturbations to affect the composition of the upper troposphere. Enhanced concentrations of isoprene and its degradation products are simulated in the upper troposphere, and, on a global-mean basis, land cover change had a stronger impact on ozone in the upper troposphere (inline-formula+0.5 ppbv) than in the lower troposphere (inline-formula<0.1 ppbv increase). The positive climate forcing from ozone changes (inline-formula+9.2 mW minline-formula⁻²) was partially offset by a negative forcing (inline-formula−0.8 mW minline-formula⁻²) associated with an enhancement in secondary organic aerosol (SOA). The sign of the net forcing is sensitive to uncertainty in the SOA yield from BVOCs. The global-mean ozone forcing per unit of regional oil palm expansion is inline-formula+1 mW minline-formula⁻² Mhainline-formula⁻¹. In light of expected continued expansion of oil palm plantations, regional land cover changes may play an increasingly important role in driving future global ozone radiative forcing.