Fig. 5: Atmospheric composition response and BVOC feedback from an increase in CO₂ driving an increase in BVOC emissions (E_BVOC).

In (a) only aerosols are considered yielding a negative feedback (adapted from²³) whereas in (b) chemistry and oxidants are also allowed to respond, leading to a more complex response. Aerosol optical depth (AOD) is a measure of aerosol scattering while IRF_DRE and CRE correspond to the forcing from changes to the aerosol direct radiative effect and aerosol cloud interactions respectively. Dashed lines in (b) show important oxidant-driven responses including reduced OH driving (A) increased secondary organic aerosol (SOA) lifetime and climatic impact, (B) greater vertical transport of O₃ precursors and thus O₃ forcing (SARF_O3), (C) increased CH₄ lifetime (\({\tau }_{C{H}_{4}}\)) and climatic impact and (D, E) reduction in gas phase SO₂ oxidation with attendant decreases in H₂SO₄, new particle formation, cloud condensation nuclei (CCN), cloud droplet number concentration (CDNC) and cloud albedo. The strength of the feedback for each loop is shown by the feedback factor (see Methods) for the Strat-Trop mechanism (\({\alpha }_{{ST}}\)) and CRI-Strat 2 mechanism (\({\alpha }_{{CS}2}\)) in parentheses.