CMIP7 historical greenhouse gas forcing and steps towards sustained releases

Climate forcings are the input drivers to coupled climate models (AGOCMs) and earth system models (ESMs). They are routinely used as part of the coupled model intercomparison project (CMIP). Here we present the historical greenhouse gas forcing used in the seventh phase of CMIP (CMIP7) and compare it to its predecessors from CMIP6 and CMIP5. We show that revised methods and input data have had little effect on historical estimates of greenhouse gas forcing, but that greenhouse gas forcing has continued to increase since 2015 (the end of the CMIP6 historical experiment), even if forcing from some specific gases has decreased. Beyond the greenhouse gas forcings, there are a number of other forcings involved in CMIP. Following on from our involvement in the CMIP Forcings Task Team, we present an outline for moving towards sustained, roughly annual, releases of these forcings and discuss the challenges for realising this possibility.