Climate feedback from vegetation emissions strongly dependent on modelling of atmospheric chemistry.
- 1Centre for Atmospheric Science, Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
- 2Department of Biosciences, University of Sheffield, Sheffield, S10 2TN, UK
- 3National Centre for Atmospheric Science, Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
- 4National Centre for Atmospheric Sciences, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
- 5School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
Emissions of volatile organic compounds from vegetation (BVOCs) affect climate via changes to O3, CH4, aerosol and clouds. BVOC emissions themselves exhibit dependencies on climate (causing a feedback) and land use change including certain climate change mitigation strategies. Therefore, emissions are predicted to change under future climate pathways yet there remains considerable uncertainty between climate models in the sign and magnitude of the net climatic impact BVOCs (Thornhill et al., 2021).
One contributor is uncertainty in the description of BVOC chemistry, hitherto minimally assessed in a climate context despite recent scientific advances. In the climate model UKESM1 we evaluate the influence of chemistry by comparing the response to a doubling of BVOC emissions in a pre-industrial (PI) atmosphere using standard and state-of-the-art chemistry mechanisms, the latter featuring recent improvements in chemical understanding. The feedback is positive in both mechanisms with the negative feedback from enhanced aerosol scattering outweighed by positive feedbacks from O3 and CH4 increases and aerosol-cloud interactions (ACI). We suggest the ACI response, contrary to past studies, is probably driven by reductions in cloud droplet number concentration (CDNC) via suppression of gas phase SO2 oxidation.
The net feedback is 43% smaller with state-of-the-art chemistry due to lower oxidant depletion which yields smaller increases in CH4 and smaller decreases in CDNC. Thus, the PI climate in UKESM1 is only about half as sensitive to a change in BVOC emissions with state-of-the-art chemistry, highlighting the important influence of simulated chemistry.
The role of chemistry is also compared to the inter-model variation in BVOC forcing. We suggest the variation in chemistry between models is likely to play a large role in explaining the variation in the BVOC feedback from O3 and CH4 changes and a smaller role in the aerosol feedback, highlighting the need to improve the descriptions of BVOC chemistry and BVOC-aerosol coupling in tandem to improve assessments of the climatic impact of future BVOC emission changes.
How to cite: Weber, J., Archer-Nicholls, S., Abraham, N. L., Shin, Y. M., Griffiths, P., Grosvenor, D. P., Scott, C. E., and Archibald, A. T.: Climate feedback from vegetation emissions strongly dependent on modelling of atmospheric chemistry., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6446, https://doi.org/10.5194/egusphere-egu22-6446, 2022.