Wide-scale tree planting is a popular climate change mitigation strategy but will drive increases in the emissions of biogenic volatile organic compounds (BVOCs).
BVOCs influence atmospheric oxidising capacity and thus the greenhouse gases O3 and CH4, as well as producing aerosols which scatter radiation and influence cloud properties. However, the description of BVOC chemistry in climate models lags well behind the latest understanding. BVOC emissions are also highly dependent on climate, driving a feedback loop. The opposing effects of these composition changes and uncertainty in the chemistry lead to uncertainty in the sign and magnitude of the BVOC-feedback and so the efficacy of re/afforestation.
We assess the feedback and how it is affected by BVOC chemistry by comparing standard and state-of-the-art chemical mechanisms. After doubling BVOC emissions, positive forcings from increases in O3 and CH4 and reduced cloud reflectivity outweigh the negative forcing from the enhanced aerosol scattering. However, when state-of-the-art chemistry is used, the smaller depletion in oxidants yields a 40% smaller feedback, highlighting the important role oxidants and chemistry have on the understanding of a key climate process.