"Moscow weather,'' I call the cool, sunny, breezy weather we've been having most of this month. At its best, summer in the Russian capital is like this. But what this really is is ''Pinatubo weather.''
Last year's volcanic eruption in the Philippines threw so much dust and ash into the atmosphere, filtering the sunlight, that the world's climate will cool by a degree or two for a year or two. That's a much more sudden and drastic change than the ''global warming'' scenario we are asked to worry about.
Pinatubo's cloud throws perspective on another environmental anxiety, the yawning ozone hole. Last February the National Aeronautics and Space Administration announced that it had detected high levels of chlorine monoxide over the Northern Hemisphere for the first time. This chemical is an ozone-eater, implicated in the thinning of the protective ozone layer over the South Pole.
Within days, Sen. Albert Gore, D-Tenn., introduced a bill to speed the phasing-out of chlorofluorocarbons, and within a week President Bush had imposed the speeded-up timetable by regulatory fiat.
But the chlorine monoxide didn't come from chlorofluorocarbons; came from Mount Pinatubo. Every year volcanoes and other natural sources release several thousands of times as much chlorine into the atmosphere as man-made spray cans and chemical processes.
Big-picture environmentalism is addicted to catastrophe. ''Global warming'' posits that a build-up of atmospheric carbon -- from our smokestacks and our automobiles -- will trap heat as a greenhouse does, raising temperatures over the whole planet, expanding the deserts and shifting climate zones.
In fact the earth has been in a warming trend for several thousand years, since the end of the last Ice Age. How much may be added to nature's own warming by human industrial activity is uncertain; but according to Dixy Lee Ray, former chairman of the Atomic Energy Commission, four fifths of the carbon entering the atmosphere each year comes from natural processes.
During the Cold War, ''nuclear winter'' became a favorite tribulation. A nuclear war, it was hypothesized, would act like a super-Pinatubo, throwing up dust and ash and blotting out the sun, plunging the planet into perpetual winter. The number crunchers soon worked out that there was not enough fuel -- enough buildings and bodies and trees -- to burn and generate that much smoke. But ''nuclear winter'' survived as a fantasy to express our dread of apocalyptic war.
The Soviet Union a few years ago had a scheme on the drawing boards to reverse the flow of the Siberian rivers that run north to the Arctic Ocean. Turned south, they could irrigate arid Central Asia. American environmentalists lobbied against the Soviet scheme on two incompatible grounds:
* Without the moderating effect of the fresh-water rivers, the Arctic Ocean's salinity would increase, lowering its freezing point. Less ice would form, causing less sunlight to bounce off the polar regions. The process would accelerate, melting the ice cap, raising sea level and drowning coastal cities everywhere.
* Without the moderating effect of the warmer river flow, the Arctic Ocean temperature would drop, raising its freezing point. More ice would form, causing more sunlight to bounce off the polar regions. The process would accelerate, triggering a new ice age.
Either of these scenarios is plausible, though they can't both be true simultaneously. But the environmentalists pitched both as scientifically inevitable. Needless to say, the Russians weren't too impressed with the rigor of American environmentalists. (They finally gave up the project as too costly.)
What accounts for the John the Baptist mentality of big-picture environmentalists? (''You brood of vipers!'' howled John, calling sinners to repentance in the face of ''the wrath to come.'')
Environmentalists sometimes say they have to raise their voices to get their message taken seriously. In other words, a Big Lie is all right if it's in a good cause.
But surely a greater danger is that environmentalist hyperbole deepens hopelessness and cynicism and discourages activism that could be directed at real problems such as clean air, pure water and open spaces. In fact, there is a lot of good news. American cities are less smoggy; fish have returned to Lake Erie; more trees and more songbirds grow in America than when the first European settlers arrived.
Instead of crying doom, the environmentalists should be taking credit and assuring us that we can do a lot if we set our minds to it.
Hal Piper is editor of the Opinion * Commentary page.