Climate Science Has Looked at Clouds From Both Sides Now, But Really Don't Know Clouds At All

Like Joni Mitchell, climate science and scientists have looked at both sides of clouds and found them to be the most perplexing and uncertainty causing phenomenon that they, and climate modeling generally, face in their search for the Holy Grail of 'Equilibrium Clime Sensitivity'. The most widely used climate models - general-circulation models, energy-balance models and coupled climate models - do not simulate clouds with reasonable accuracy and some related hydrological processes (in particular those involving upper tropospheric humidity). Problems in the simulation of clouds and upper tropospheric humidity, remain worrisome because the associated processes account for most of the uncertainty in climate model simulations of anthropogenic climate change.

A less commonly used concept, the Earth system sensitivity (ESS) includes the effects of more short and long term feedbacks. Including these extra feedbacks [lots more on positive and negative feedbacks tomorrow-ed.] make the ESS sensitivity results larger than the other popular Global Climate Models — possibly twice as large — but also mean that it may or may not apply to current conditions.

The biggest uncertainty is that seen from below, clouds emit infrared radiation back to the surface, and so exert a warming effect; seen from above, clouds reflect sunlight and emit infrared radiation to space, and so exert a cooling effect. Whether the net effect is warming or cooling depends on details such as the type and altitude of the cloud. These details were poorly observed before the advent of satellite data and are difficult to represent in climate models. Plus the confounding fact that as time goes on global warming is expected to change the distribution and type of clouds.

In addition, the existence of, but not the atmosphere's sensitivity to, human-made greenhouse gases (GHGs) is known through experimentation, climate forcing caused by human-made aerosols is practically unmeasured. Aerosols are fine particles suspended in the air and often concentrated in clouds, such as dust, sulfates, and black soot. Aerosol climate forcing is complex, because aerosols both reflect solar radiation to space (a cooling effect) and absorb solar radiation (a warming effect). Plus atmospheric aerosols can alter cloud cover and cloud properties. Therefore, precise composition-specific measurements of aerosols and their effects on clouds are needed to assess the aerosol role in climate change.

Yikes...the remaining uncertainty caused by clouds is due to other interdependent feedbacks in the system like the water vapor content of individual cloud formations. Tomorrow The Mud Report will try to explain the most widely debated negative feedbacks [those often stressed by opponents of the 'consensus'] - the chemical weathering process, blackbody radiation, net primary productivity and Le Chatelier's principle.

That's enough for now, let's end this cloudy discussion with Hendrik Tennekes, retired Director of Research, Royal Netherlands Meteorological Institute, who says, "Science may be described as the art of systematic oversimplification, the art of discerning what we may with advantage omit. From this perspective, those that advocate the idea that the response of the real climate is adequately represented in climate models have an obligation to prove that they have not overlooked a single nonlinear, possibly chaotic feedback mechanism that Nature itself employs." Which of course is impossible because there are so many types of non-linear feedback that Mother Nature routinely employs it makes the exercise of climate modeling more like a trip to Vegas to study probabilities than anything else.