The Radiative Forcing Model Intercomparison Project is characterizing and assessing calculations of radiative forcing for the climate models participating in the current generation of intercomparisons (CMIP6). RFMIP complements the parallel Aerosol and Chemistry MIP, which focuses on the impacts of aerosols and atmospheric composition on air quality and climate, and the Precipitation Driver and Response MIP, which is focused on how perturbations to composition affect the net cooling of the atmosphere, and hence the global-mean precipitation.
RFMIP includes two efforts to assess the radiative parameterizations used in climate models. These build on a long history of such comparisons in the radiation community but extend the scope to the global scale using sampling strategies that accurately represent the global, annual mean using a number of profiles small enough to make benchmark calculations feasible. In this talk I will share results from the global assessment of radiative transfer parameterizations in radiative forcing in clear, aerosol-free conditions under conditions ranging from the present-day (to which parameterizations are tuned) through the pre-industrial to the Last Glacial Maximum, and into the future conditions of quadrupled and octupled carbon dioxide concentrations used to probe climate sensitivity. Line-by-line calculations agree with one another to within a percent or so. This largely reflects broad reliance on the same underlying spectroscopic data bu suggests that benchmark estimates are feasible.
At this writing few results from parameterizations are available but initial results suggest that the range of errors is diverse, especially in conditions far from present-day. I will interpret in light of results from PDRMIP and, to the extent available, AerChemMIP.
A second effort, to assess the treatment of aerosols, is described in a separate presentation.