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Mysterious Clouds More Common Due to Climate Change?

Christine Dell'Amore in San Francisco, California
National Geographic News
December 11, 2007
 
Mysterious "night-shining clouds" that light up the polar skies have become more luminous and frequent in recent years—and climate change may be the culprit, scientists announced Monday.

So-called noctilucent clouds, which streak across the sky in vibrant colors during polar summers, are ten times brighter than previously believed, according to recent data from NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite.

The data, collected during two polar cloud seasons, also suggest the formations appear daily, are more widespread, and have started to form at lower latitudes than before.

Climate Change Canary

Night-shining clouds are made mostly of ice particles that form when water vapor condenses onto atmospheric dust.

The AIM mission is the first detailed exploration of the clouds, which form about 50 miles (80 kilometers) above Earth's surface—"literally on the edge of space," AIM principal investigator James Russell III said yesterday at a press briefing at the American Geophysical Union fall meeting in San Francisco, California.

The air there is a thousand times drier than the Sahara, and the temperature can drop to minus 235 degrees Fahrenheit (minus 148 degrees Celsius)—ideal conditions for creating clouds.

A likely explanation for the clouds' surge is that temperatures in the upper atmosphere have gotten even colder due to the build-up of carbon dioxide in the atmosphere, Russell said.

Yearly emissions of carbon dioxide levels have grown about 20 percent since 1990. Most scientists agree the buildup is causing climate change and heating up Earth's surface.

In the upper atmosphere, however, carbon dioxide does not act like a thick, heat-trapping blanket.

Instead it forms a thin layer, allowing heat to escape, temperatures to drop, and ice particles to form.

"[These] clouds are the mine's canary of global warming," Russell told National Geographic News.

No Other Plausible Reason

The evidence linking carbon dioxide to changes in night-shining clouds is still tentative, Russell said.

But "in all honesty, we don't know of any other plausible reasons why it wouldn't be global climate change," he said.

"If that's true, that says not only are we changing the atmosphere where we're living, we're changing a very remote, rarified part of our atmosphere."

Such far-reaching change means that "we need to be concerned," Russell said.

"If [the cloud changes] are indeed tied to carbon dioxide buildup, here's another confirming reason we should strive to do something about it."

"Exquisite Thermometer"

AIM also discovered "dramatic changes" in cloud behavior, said Scott Bailey, AIM's deputy principal investigator.

The data suggest the clouds are highly variable, rotating every five days according to minute shifts in temperature—even as little as 5 degrees Fahrenheit (2.7 degrees Celsius).

"These clouds are exquisite thermometers," he said.

"Now we're able to see the whole life cycle [of a cloud] for the first time," Bailey told National Geographic News.

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