Clouds in the Climate Models

Do the tropics hold the secret to a cooler world?

Is there a natural heat vent in the clouds over the tropics that may substantially cool down projected man-made global warming? Possibly yes, according to a study published last spring in the Bulletin of the American Meteorological Society (BAMS) by Massachusetts Institute of Technology climatologist Richard Lindzen and his colleagues at NASA's Goddard Spaceflight Center.

Lindzen, after looking at cloud data in the tropical Pacific, is suggesting that warmer sea surface temperatures would increase the production of rainy cumulus clouds, which would, in turn, reduce the amount of moisture that remains in the cold upper atmosphere. This is important because cumulus clouds reflect more sunlight back into space before it can heat the earth and because the rain cumulus clouds release leaves less moisture to form high icy cirrus clouds that act as insulating blankets and block heat from escaping into space. Lindzen likens this process to the iris of an eye--a mechanism that adjusts to let in or keep out something, light in the case of the iris, and heat in the case of the atmosphere.

If the effect is as strong as Lindzen's research indicates it might be, it would substantially reduce the amount of future global warming, despite current projections by climate computer models that don't account for this effect. Many computer models project that in response to a doubling of carbon dioxide in the atmosphere (produced by burning fossil fuels), the world would warm by 1.5 to 4 degrees centigrade. The BAMS study suggests that Lindzen's effect, by counteracting the man-made greenhouse effect, would reduce the range of possible temperature increases to 0.64 to 1.6 degrees centigrade. Such a temperature increase over a century would certainly not be a climate catastrophe. Lindzen does caution that "the present results must still be regarded as tentative at best."

Lindzen's study caused considerable consternation among ideological environmentalists. When the activists' latest bete noire Bjorn Lomborg wrote about Lindzen's work in his new book, The Skeptical Environmentalist, the World Wildlife Federation (WWF) and the World Resources Institute (WRI) sent out a press release to environmental journalists suggesting that citing Lindzen's paper was "pseudo-science." WWF and WRI went so far as to claim that Lindzen's work had appeared in a minor journal and had not been peer-reviewed. (WWF and WRI have since removed that canard from the WRI Web site.)

Now two new studies have been published in the February 1 issue of Science showing that something is indeed going on in the tropics that is consistent with Lindzen's iris effect (though it does not confirm it). Researchers at two NASA institutes have found that the tropics have become less cloudy over the past 15 years. According to the paper by Junye Chen et al., "satellite observations suggest that the thermal radiation emitted by Earth to space increased by more than 5 watts per square meter, while reflected sunlight decreased by less than 2 watts per square meter, in the tropics over the period 1985-2000." In other words, on balance, more heat escaped into space than was added by the additional sunlight that fewer clouds let in. This process tends toward cooling down the atmosphere.

Why are these studies important? Because as the Lindzen study points out, "Whether the iris feedback ultimately proves as effective as our results suggest, the inability of existing models to replicate the relevant observations suggests the need for model improvement in an area potentially crucial to the determination of climate sensitivity." In other words, the current climate models may be missing important effects that would dramatically reduce their projections of future global warming.

A new Science study by Bruce Wielicki et al. also concludes that the changes it uncovered "are not well predicted by current climate models….Indeed, current assessments of global climate change have found clouds to be one of the weakest components in climate models. This leads to a three-fold uncertainty in the predictions of the possible warming over the next century."

It is evident from these studies and others that our best climate models are still sorely lacking. Nevertheless, using the excuse that the models say burning fossil fuels could lead to catastrophic global warming, environmental activists are stampeding the world's policy makers into adopting costly international agreements like the Kyoto Protocol that are aimed at dramatically cutting fossil fuel use. Those agreements are essentially an attempt to centrally plan humanity's energy future for the next century. Given the great uncertainties in the models and their failure to account for crucial atmospheric effects like those uncovered in these studies, is that really such a good idea?