Extended Data Table 1 Design of CESM (CAM-Chem) benchmark model simulations

From: Natural short-lived halogens exert an indirect cooling effect on climate

  1. &The pre-industrial methane emission inventory used here39 results in a global mean surface CH4 mixing ratio of 722 ppbv for the pre-industrial NAT simulation. For present-day, cyclical methane emissions for year 2020 were used39. Long-lived gases lower boundary conditions (LBC) for pre-industrial times are from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)70,106, assuming that there was no emission change between 1750 and 1850. To obtain a realistic representation of the present-day stratospheric halogen burden, the long-lived LBCs were fixed to year 2020 for the SAOD-2010 scenario A176. The main anthropogenic pollutants sources for year 2020 follow the Chemistry Climate Model Initiative (CCMI) recommendation for present-day conditions51 which are cycled during the 15-years integrations.
  2. $Climate-induced changes in natural halocarbon fluxes follow the cli+bio sensitivity described in ref. 37, which includes both changes in physical (mainly due to sea-surface temperature (SST)) and biogeochemical (mostly related to marine primary production) factors. The short-lived halocarbon oceanic emissions during pre-industrial conditions are assumed to be identical to year 1850 (ref. 39). The sea-salt aerosol (SSA)-dehalogenation source for bromine and chlorine is based on ref. 55, with an updated scheme for HCl release due to the acidification of tropospheric aerosols56. Oceanic emissions of HOI/I2 are based on ref. 38, while sea-ice polar emissions follow ref. 57. All online inorganic halogen emissions are computed based on SST and sea-ice conditions representative of each period of time.
  3. £Anthropogenic sources and LBCs of short-lived chlorocarbons during present-day conditions are based on refs. 64,68,69. For pre-industrial sensitivities anthropogenic SLHs were forced to zero, while for future simulations SLHs emissions and LBCs were assumed to linearly decrease down to zero after reaching their maximum values in year 2030 (ref. 39). The continental sources of inorganic halogens are described in ‘Emissions inventory of global anthropogenic halogens’ in Methods.
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