It has become standard practice for many of the more alarmist climate modelers to include what are called positive feedback mechanisms in their climate models. One important such mechanism is the hypothesized role of certain kinds of clouds. Steve Milloy from Junk Science.com summarizes the effect:

Existing climate models, for example, assume that a warmer atmosphere will cause an increase in high-altitude cirrus clouds — a positive feedback into the climate system since cirrus clouds trap outgoing radiation emitted by the Earth.

When you feed the above-mentioned warming scenario — the doubling of atmospheric carbon dioxide levels causing 1.2 degrees Centigrade of warming — into a climate model that has been turbo-charged with positive feedback, the resulting estimated warming increases by 250 percent to 3 degrees Centigrade.

But new research published in the Geophysical Research Letter by at team of researchers from the University of Alabama at Huntsville calls this effect into question. It builds on earlier work by MIT’s Richard Lindzen. Here’s Milloy’s summary of the new research.

Massachusetts Institute of Technology atmospheric physicist Richard Lindzen, for example, proposed in 2001 an explanation called the “iris effect” for why amplified warming has never materialized.

Based on a limited set of data, Lindzen hypothesized that cirrus clouds and associated moisture actually work in opposition to surface temperature changes. When the Earth’s surface warms, Lindzen supposed, the clouds open up to allow heat to escape. A cooling surface, in turn, causes clouds to close and trap heat.

This elegant atmospheric self-regulatory mechanism was soon attacked for being based on limited data and the inability of other researchers to be able to identify the iris effect in other cloud and temperature data sets.

But the new research from the University of Alabama-Huntsville supports the validity of the iris effect.

Analyzing six years of data from four instruments aboard three NASA and NOAA satellites, the UAH researchers tracked precipitation amounts, air and sea surface temperatures, high- and low-altitude cloud cover, reflected sunlight and infrared energy escaping out to space.

Rather than the hypothesized positive feedback of the climate models, the UAH data actually shows a strong negative feedback. As the tropical atmosphere warms, cirrus clouds decrease, allowing infrared heat to escape from the atmosphere to outer space.

“To give an idea of how strong this enhanced cooling mechanism is, if it was operating on global warming, it would reduce [climate model-based] estimates of future warming by 75 percent,” said UAH researcher Roy Spencer in a media release.

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