Problems of CMIP5 Climate Models with Tropical Low Clouds
Nam, C., Bony, S., Dufresne, J.-L. and Chepfer, H. 2012. The 'too few, too bright' tropical low-cloud problem in CMIP5 models. Geophysical Research Letters 39: 10.1029/2012GL053421.
In studying this unresolved dilemma, Nam et al. analyzed "outputs from multiple climate models participating in the Fifth phase of the Coupled Model Intercomparison Project (CMIP5) using the Cloud Feedback Model Intercomparison Project Observations Simulator Package (COSP), and compared them with different satellite data sets," including "CALIPSO lidar observations, PARASOL mono-directional reflectances, and CERES radiative fluxes at the top of the atmosphere." So what did their comparison reveal?
In the words of the four French researchers, "the current generation of climate models still experiences difficulties in predicting the low-cloud cover and its radiative effects." In particular, they report that the models: (1) "under-estimate low-cloud cover in the tropics," (2) "over-estimate optical thickness of low-clouds, particularly in shallow cumulus regimes," (3) "poorly represent the dependence of the low-cloud vertical structure on large-scale environmental conditions," and (4) "predict stratocumulus-type of clouds in regimes where shallow cumulus cloud-types should prevail." However, they say that "the impact of these biases on the Earth's radiation budget ... is reduced by compensating errors [italics added]," including "the tendency of models to under-estimate the low-cloud cover and to over-estimate the occurrence of mid- and high-clouds above low-clouds."
Given such findings, it seems more than odd that leaders of numerous nations are forging ahead with energy policy prescriptions for halting global warming - which has been non-existent for close to two decades now - based on climate change projections derived from mathematical models harboring acknowledged problems that are supposedly overcome by compensating errors.
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