Go to the woods. Look around. Something's missing. There's no crimson in the palette. The warm weather has made this a faded autumn, a jaundiced autumn, the autumn of our discontent. Nature, unlike the government, is refusing to operate in the red.

The trees haven't been cold enough. "If the plants are not under stress during the time that they are actively photosynthesizing, the secondary pigments don't develop in the leaf," explains Bill Anderson, regional chief scientist for the National Park Service.

In other words, if it isn't cold, the leaves don't become red, orange and gold.

What happens next? Will the leaves explode in color at the last second?

"They'll turn brown and the leaves will fall off," Anderson says.

"The colors are definitely off this year from what they normally would be," agrees Lester Brown, director of the Worldwatch Institute, an environmental research organization. "South of New York there's not much color. In downtown Washington we're going to lose our leaves before they turn."

Brown and his colleagues put out an annual report called "State of the World," and he's sensitive to these marginal changes, the unseasonal weather that jibes uncomfortably with what the computer models predict will happen in a world running a slight temperature. He fears that the much-debated "greenhouse effect" -- global warming aggravated by such things as the burning of fossil fuels -- may be fouling our fall.

"They're coming more frequently now, years in which there's not much color. That's my sense, having lived in Washington since the late '50s," he said.

You could say it doesn't matter much. The losses are on the margin of an unmeasurable aesthetic. It is the kind of deficit that cannot be plugged into the economists' equations, the loss of a few epiphanies, a couple of dozen smiles, and maybe somewhere a young couple decide not to detour through the woods, where, in a moment of passion inspired by nature's glories, they would have conceived the child who, had he existed, would have eventually assassinated the 21st-century psychopathic dictator who pressed the button that released the anthrax bombs that destroyed civilization as we know it. And you say it doesn't matter.

The non-hysterical person would have to admit there are some fabulous bursts of gold in the sugar maples, some yellow action in the cottonwoods, an occasional red oak that lives up to the billing, but for the most part the leaves seem confused, stuck between green and brown, laden with chlorophyll when they should be showing off their anthocyanin and carotene and xanthophyll. You could plot the great trees on a map with a single box of red pins: a fine maple on Macomb two blocks off Connecticut, a good bank of oaks near Pierce Mill in the Rock Creek Park, and so on.

The view from Skyline Drive in the Shenandoah Valley has been unspectacular. It was also a mediocre season in Vermont, the foliage capital of the United States. Hubert Vogelmann, chairman of the botany department at the University of Vermont in Burlington, says, "Somehow the colors are not as bright anymore. I just think overall they're not as intense."

You have to respect a tree on so many counts. A tree has a kind of individuality, so that one might be bright gold while a neighbor of precisely the same species is still mired in off-green. A tree has patience; it is still there at your childhood home, years after your family moved away. A tree even knows parlor tricks, like getting water from the roots to the leaves without use of moving parts, pulleys or conveyor belts.

And that trick they do with the leaves, it's something we take for granted.

Leaves are finely tuned instruments. To become colorful they need bright sunlight and cold nights. The tree's metabolism slows down, chlorophyll disintegrates as it is hammered by light, and as the green disappears, the relatively sparse red and yellow pigments beneath are unmasked. If the weather is too warm it ruins the entire recipe. The green never clears out before the leaf turns brown.

"That chemical system, degradation of chlorophyll, is cued by temperature," says Dave Schimel, an ecologist at Colorado State University. As a scientist he's not going to say anything alarming, but he acknowledges that fears of a diminished autumn due to global warming are not completely nutty. "In principle, it could happen."

From Oct. 6 to 15, when a cold snap should have shocked at least some color into the leaves, the average high temperature in metropolitan Washington was 82.4 degrees. Now it is early November and shirt sleeves are still in order. At Baltimore-Washington International Airport it is the warmest year on record, and it is the second warmest at National Airport. Before the year is out, National Weather Service meteorologist David Miskus said yesterday, 1990 may go down as the warmest year in the Washington area since the Grant administration.

There is a larger buzz among climatologists, that 1990 will set a global record as well. Philip Jones, a climatologist at the University of East Anglia in England, testified before a Senate panel in early October that 1990 would set the new mark. The five warmest years previously were in the 1980s. Scientists are not convinced that global warming has begun. This could be a blip on the chart, a normal aberration, if such a term can be used.

Scientists must be precise. They have their margins of errors, their windows of doubt. This week, many of the world's top climatologists are meeting in Geneva at the World Climate Conference. Years ago there was probably no such thing as a World Climate Conference. The weather took care of itself. And the fact that they're meeting in Geneva, that place where they discuss nerve gas treaties and so forth -- it's a bad omen.

For a real injection of gloom one might talk to Bill McKibben, author of "The End of Nature." It is a book of immense gravity, even the blurbs on the jacket are scary ("It's a matter of life and death to read this book," says one from Harold Brodkey). McKibben said this week that he's enjoyed a great fall up in the Adirondacks, but still feels the weight of global warming. That's because nature used to be something apart from man, something immutable, greater, untouchable, but now is just another human artifact. "It's finally dawning on us that we do have the power to alter the world in fundamental ways," McKibben says. "Before, the leaves changing color was something that just happened, and now we're beginning to understand that we may have a large role."

He adds portentously, "The loss of foliage is going to be the least of our problems."

It's gotten to where you can't see the forest for the Themes: degradation, regression, death. You wanted a little fresh air and exercise and suddenly you've got global warming on the brain, and that ozone thing, and the corals that are dying down there in the Caribbean, and those fish that have tumors, on and on.

Nature just doesn't seem natural anymore.