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Bad News Beautifully Packaged

Pollution usually brings to mind ugly things: smoke and smog, foul waters, litter, junk, crud are the understood symbols of a stressed Earth. Yet here in the high latitudes, we have a good view of what turn out to be some lovely warnings of pollution.

They're called noctilucent clouds. The name means that they shine at night, and it's apt. Noctilucent clouds gleam in late-summer evenings as if they're lit from within, but it's sunlight that makes them shine. They look brilliant in the evening sky because they are so high that everything lower is in shadow while they're still in sunshine. Noctilucent clouds lie 82 kilometers (51 miles) above the earth's surface; for ordinary clouds, that's too high.

A good thunderhead, at about seven miles up, is bumping into the realm of what we usually think of as the highest of clouds, the wispy cirus. Seven times higher, beyond the stratosphere and up into the mesosphere, conventional wisdom holds that there just isn't enough water vapor, nor enough dust for any vapor to condense upon to make droplets, for clouds to form. At least there shouldn't be, but there the noctilucent clouds are. They've aggravated scientists for more than a century.

Which is another peculiar thing about noctilucent clouds: no one ever reported seeing one before 1885, when a German scientist wrote of them. Soon other observers documented their appearance over Great Britain, Europe, and Russia. They were considered rare over North America until researchers at the Geophysical Institute began studying them over Fairbanks in 1962. Graduate student Ben Fogle made them his special field of study, and helped establish that it had been only a lack of organized observations at high latitudes in the Western Hemisphere that had made them seem rare here.

During the following flurry of research here and elsewhere, a good bit of information was amassed about noctilucent clouds. Sometimes they covered huge areas; four of the 50-odd displays seen during 1963 covered more than a million square kilometers of sky. They could last for hours, though portions of them could fade away in a few minutes. Often they provided wonderful photographs, and were recorded not just near Fairbanks but from Homer, Gustavus, and virtually all over the north.

Interesting though all these things were, they amounted to mere curiosities. The noctilucent clouds seemed to be just clouds, great streaky patches of ordinary water vapor, frozen because of their chilly altitude.

Recently an international team of investigators suggested that noctilucent clouds are becoming brighter and more common because more water exists 82 kilometers above the earth. They think the clouds turned on, so to speak, in 1885 because two years earlier the great volcanic explosion of Krakatoa occurred: the blast that destroyed the island mountain sent tons of vapor and dust into the stratosphere. In another two years, physical processes would carry the eruption's products high enough to cause noctilucent clouds.

So far, so good; in fact, about ten years after he started studying the clouds, Fogle and others had published work relating them to volcanic activity. But that's not all there is to it. The new research predicts there will be bigger and better cloud displays because human activity is putting more methane into the atmosphere.

Methane moves up through the atmosphere. Above about 30 kilometers, it breaks down and recombines with other atoms and molecules; water is one of the products. The amount of methane is increasing. Air bubbles trapped in ancient polar ice show much lower concentrations of it before the industrial age. When the scientists ran calculations on the effect of increased methane, given what they knew about its behavior and the conditions high above the earth, back came the result: more and brighter noctilucent clouds.

All of which would mean little but another lovely phenomenon in our night skies, except that methane is a greenhouse gas. It's even more effective at trapping heat than is carbon dioxide, the most commonly named culprit in climate change. Unless a volcano has exploded, take those beautiful night-glowing clouds as warnings of trouble brewing.