Radiative forcing by long‐lived greenhouse gases: Calculations with the AER radiative transfer models

TLDR

Radiative forcing from long‑lived greenhouse gases is a major driver of recent climate change, and accurate representation of water vapor, ozone, and LLGHG radiative processes is essential for general circulation models, with AER models also reproducing surface fluxes well. The study evaluates the capability of AER radiation models to compute long‑wave and short‑wave radiative forcing for clear‑sky scenarios, building on previous RTMIP intercomparison work. AER line‑by‑line and broadband models produce radiative forcing and heating profiles that agree closely with high‑resolution RTMIP results, with broadband calculations within ±0.2 W m⁻² of LBL values and heating perturbations within a few hundredths K d⁻¹, outperforming GCM radiation codes.

Abstract

A primary component of the observed recent climate change is the radiative forcing from increased concentrations of long‐lived greenhouse gases (LLGHGs). Effective simulation of anthropogenic climate change by general circulation models (GCMs) is strongly dependent on the accurate representation of radiative processes associated with water vapor, ozone, and LLGHGs. In the context of the increasing application of the Atmospheric and Environmental Research, Inc. (AER), radiation models within the GCM community, their capability to calculate longwave and shortwave radiative forcing for clear sky scenarios previously examined by the radiative transfer model intercomparison project (RTMIP) is presented. Forcing calculations with the AER line‐by‐line (LBL) models are very consistent with the RTMIP line‐by‐line results in the longwave and shortwave. The AER broadband models, in all but one case, calculate longwave forcings within a range of −0.20 to 0.23 W m −2 of LBL calculations and shortwave forcings within a range of −0.16 to 0.38 W m −2 of LBL results. These models also perform well at the surface, which RTMIP identified as a level at which GCM radiation models have particular difficulty reproducing LBL fluxes. Heating profile perturbations calculated by the broadband models generally reproduce high‐resolution calculations within a few hundredths K d −1 in the troposphere and within 0.15 K d −1 in the peak stratospheric heating near 1 hPa. In most cases, the AER broadband models provide radiative forcing results that are in closer agreement with high‐resolution calculations than the GCM radiation codes examined by RTMIP, which supports the application of the AER models to climate change research.