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Downward atmospheric longwave radiation in CMIP5 models

05 Jul 2023 | Science Notes

From the CO2Science Archive: Background: The authors write that “atmospheric downward longwave radiation at the surface (Ld) quantifies the atmospheric greenhouse effect,” which makes its evaluation one of the primary objectives of those who seek to divine its future impact on the planet. What was done: According to Ma et al., the modeled Ld of 44 general circulation models (GCMs) that participated in the CMIP5 program were compared with land-based observations acquired at 47 sites of the Baseline Surface Radiation Network (BSRN), 51 sites of the Coordinated Energy and water cycle Observations Project (CEOP), 34 sites from the AmeriFlux network over the United States, 18 sites from the AsiaFlux network in Asia, and 12 sites where buoy-based measurements were made over tropical oceans over the period 1992-2005.

Paper reviewed: Ma, Q., Wang, K. and Wild, M. 2014. Evaluations of atmospheric downward longwave radiation from 44 coupled general circulation models of CMIP5. Journal of Geophysical Research: Atmospheres 119: 4486-4497.

What was learned
The three researchers determined, among a number of other things, that (1) “GCMs in CMIP5 could not accurately simulate the diurnal variation of surface temperature and water vapor,” and that (2) “CMIP5 GCMs are still poor in producing monthly anomalies of Ld,” which is likely due to (3) “the GCM’s poor performance in simulating seasonal variation of clouds and monthly anomalies of air temperature and water vapor.”

What it means
In light of these several shortcomings, we have to ask ourselves the proverbial question about the integrity of the world’s most up-to-date climate models: are we there yet? Apparently not; for however close the models may seem to be getting to replicating reality, they still fall significantly short of the mark.

One comment on “Downward atmospheric longwave radiation in CMIP5 models”

  1. If you really follow the science, CO2 is a highly efficient absorber of IR radiation, so efficient that it sucks up the vast majority of IR in the first few hundred feet of atmosphere. When the CO2 absorbs the IR, it gets warmer. That heat can do 3 things: 1) It can re-radiate up to be absorbed by higher layers; 2) It can re-radiate down and be absorbed the ground to be re-radiated up again; or, 3) transfer it’s heat to oxygen and nitrogen by conduction which transport the heat upward by convection while simultaneously carrying water vaporized from the surface. This causes a phenomenon called WEATHER.
    For all intents and purposes, neither upward nor downward radiation is of any importance. The convection of heat and the transport of water vapor are the only important mechanisms—and these are independent of modern CO2 concentrations.

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