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Smoke Lowers Temperatures : N. California Fires Boost Nuclear Winter Theory

Times Staff Writer

The devastating Northern California forest fires in 1987 created a self-perpetuating inversion layer that trapped a pall of smoke over the Klamath River canyon and kept high temperatures an average of 27 degrees below normal for a week, a scientist reported today.

The dramatic temperature drops, described in a study published in the journal Science, appear to lend further credence to the nuclear winter theory, which holds that there would be catastrophic global cooling in the grim aftermath of a nuclear war.

In the small community of Happy Camp, Calif., nestled in the smoke-covered Klamath River canyon, the high temperature on Sept. 7 was 54 degrees Fahrenheit--36 degrees below normal--as thick smoke from the lightning-caused forest fires blocked out the sun’s rays.

Daily maximum temperatures during the week of Sept. 4-12 were an average of 27 degrees below normal. For the next two weeks, high temperatures hovered 9 degrees below normal in Happy Camp and nearby Orleans.

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While the findings by University of Maryland meteorologist Alan Robock do not in themselves prove the nuclear winter scenario, he said the dramatic impact of smoke on surface temperatures may be a harbinger of the cooling effect that would result if the entire planet were cast in a smoky shroud following a nuclear catastrophe.

“The cooling effect produced by smoke in the upper atmosphere . . . would be the same effect as if the whole world was at Happy Camp,” Robock said in a telephone interview.

Richard P. Turco, one of five scientists including astronomer Carl Sagan whose joint study in 1983 drew widespread attention to the nuclear winter scenario, on Thursday called the latest findings significant. He said never before had such dramatic drops in surface temperatures been predicted in the presence of low-lying smoke.

“From my point of view the most significant finding is the direct observation of strong surface cooling in the presence of layers of smoke in the atmosphere. This is the fundamental effect (of smoke in the upper atmosphere) that we first described many years ago. But, he’s found it in lower-level smoke where we wouldn’t have thought it was possible,” Turco said.

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“It’s a direct confirmation of the basic physics of the nuclear winter effect,” said Turco, a professor of atmospheric sciences at UCLA.

Inversion Layer

What made Robock’s observations particularly fascinating was his discovery that a natural inversion layer over the Klamath River canyon was actually strengthened by the forest fires, trapping more and more smoke and accelerating the dramatic declines in temperatures. An inversion layer occurs when air above is hotter than the air below, creating a lid effect that holds smoke and other pollutants nearer the ground.

“Each day, more smoke accumulated beneath the inversion, with the surface cooling produced by the blockage of sunlight strengthening the inversion and trapping more smoke . . . creating a positive feedback,” Robock reported in Science.

This closed-loop phenomena produced “much larger and longer lasting surface-temperature effects” than ever recorded before.

Robock’s findings were based on weather data collected by 246 weather stations operated by the National Weather Service and the U.S. Forest Service.

Drawing on this data, Robock was able to calculate deviations from normal temperatures in the region recorded at the time when the forest fires were well on their way toward scorching 1.1 million acres in Northern California and southern Oregon.

Much of his effort was eventually focused on the Klamath River canyon and the communities of Happy Camp, Orleans and Slater. He compared temperatures there with those at Medford, Ore., which was not as near the natural holocaust unleashed when lightning ignited 1,200 fires in the two-state region.

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“Although the small spatial scale of the cooling shown here does not by itself imply large-scale cooling in a nuclear winter scenario,” Robock wrote, “this example demonstrates that smoke can cause cooling and shows the existence of a feedback mechanism that can enhance and prolong the expected cooling.”

In an interview with The Times, Robock said, “This tells us that there are still undiscovered mechanisms in the atmosphere that could possibly make the consequences of things that humans do to the atmosphere worse than we previously thought.”

While Robock said the findings serve to lend additional credence to the nuclear winter theory, he noted that the phenomena he observed occurred in a valley that prevented the winds from blowing the smoke away. He also cautioned that in the event of a nuclear war, the cloud cover from millions of fires would be much higher in the atmosphere.

“But, it’s the same physics and the effect might be the same. It’s a lesson to us to look into the whole problem,” he said.

HOW SMOKE LOWERED TEMPERATURES--In September, 1987, smoke from major forest fires in northern California was trapped in Klamath River canyon and lowered daytime temperatures there. Chart shows temperatures in Happy Camp and Orleans, Calif., in comparison to average maximum temperatures. In Medford, Ore., which was not affected by the smoke, temperatures were closer to the seasonal average.


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