.* \[[2011](#grl53099-bib-0012){ref-type="ref"}\]), although at least one implemented diagnostic calculations in a single‐column version of the full model. We focus on the treatment of gases by considering four clear‐sky cases, with precipitable water vapor ranging from 0.32 to 4.85 cm, originally chosen for good agreement between spectral measurements at the surface and reference model calculations using estimates of the overlying atmospheric state. We further simplify the problem by specifying no aerosols and spectrally uniform surface albedo and emissivity. We perform two sets of experiments, one under the initially observed atmospheric conditions (essentially repeating the shortwave "case b" calculations of *Oreopoulos et al.* \[[2012](#grl53099-bib-0025){ref-type="ref"}\]) and a second in which the observed concentrations of CO~2~ have been quadrupled. Fluxes are reported at the top of atmosphere and the surface. Atmospheric absorption or emission (radiative divergence) is computed as the difference between net downward radiation at these two levels. Forcing is the difference between 4 × CO~2~ and present‐day conditions.

We solicited contributions from modeling centers that participate in CMIP exercises. Many provided results from the current version of their radiation parameterization; some also provided results from the version used in CMIP5 \[*Taylor et al.*, [2012](#grl53099-bib-0034){ref-type="ref"}\]. Calculations made with version 12.2 of the Line‐By‐Line Radiative Transfer Model (LBLRTM) model \[*Clough et al.*, [2005](#grl53099-bib-0006){ref-type="ref"}\] provide the benchmark, as they did for CIRC (though CIRC used a slightly older version). Participating radiation models and results from LBLRTM are detailed in the [supporting information](#grl53099-supinf-0001){ref-type="supplementary-material"}. Although our assessment does not include every parameterization used by models participating in CMIP, several parameterizations are used in more than one model, so that the radiation component