Abstract
Here I review the developments in the representation of radiation budgets in global climate models (GCMs) from a surface perspective, considering early models up to the latest model generation used in the IPCC fourth assessment report (AR4). As in previous model generations, considerable differences in the simulated global mean radiation budgets are also present in the IPCC-AR4 models, particularly in the atmosphere and at the surface. I use a comprehensive set of surface observations to constrain these uncertainties, and focus on the downward short-and long-wave radiation, which can directly be validated against the surface observations. The majority of the IPCC-AR4 models still shows a tendency to overestimate the short-wave and underestimate the long-wave downward radiation at the surface, each by 6 Wm−2 on average, a long standing problem in many GCMs. A subset of models, however, is now capable of simulating at least one of the short-or long-wave downward components adequately. Model biases in all-and clear-sky fluxes are often similar, suggesting that deficiencies in clear-sky radiative transfer calculations are major contributors to the excessive surface insolation in many of the models. No indication is found that the simulated excessive surface insolation is due to missing cloud absorption.
Highlights
The most powerful tools available to quantify and predict the consequences of human interference with climate are threedimensional general circulation models (GCMs)
Here I review the developments in the representation of radiation budgets in global climate models (GCMs) from a surface perspective, considering early models up to the latest model generation used in the IPCC fourth assessment report (AR4)
By definition, in the surface and top of atmosphere (TOA) cloud radiative forcing, have R values of 1.09, 1.10 and 1.10. This implies that the presence of clouds in the state of the art IPCC-AR4 GCMs does not substantially increase the overall absorption of solar radiation in the atmospheric column compared with the cloud-free column
Summary
The most powerful tools available to quantify and predict the consequences of human interference with climate are threedimensional general circulation models (GCMs). Anthropogenic climate change is, from a physical point of view, first of all a perturbation of the Earth radiation balance through human emission of greenhouse gases and aerosol. If these perturbations ought to be realistically simulated, it is an essential pre-requisite that the components of the Earth radiation balance are adequately reproduced in these models. Much less emphasis has been placed on the radiation balance at the surface, where no similar observational constraints have been available for comparison. The aim of the present paper is, to review and document the developments in radiation budget modelling in GCMs from a surface perspective over the last few decades, up to the latest generation of GCMs used in the 4th assessment report of the Intergovernmental Panel on Climate Change (IPCC-AR4, IPCC, 2007). The focus is on the radiative fluxes in both the short-wave ( known as solar, 0.2–4 μm) and longwave ( known as thermal or terrestrial, 4–100 μm) part of the electromagnetic spectrum
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