When I began these columns there were certain subjects that I swore to avoid. I would not write about topics of interest to few people but me, or about topics so embroiled in controversy that rational discussion seemed impossible.

Global warming is a perfect example of the second category. It has been the subject of hundreds or thousands of scientific papers, and is the basis for national regulations and proposed global treaties. It arouses fiery public arguments between those who believe this to be a huge and rising peril to the whole world and those who discount its importance or deny its existence.

So why am I writing about it? I am not a meteorologist, or a policy maker, or an expert in radiation physics or atmospheric chemistry, and I assume that you, too, are not one of these specialists. However, we are all capable of following simple logic. And some key elements of common sense and basic science - I emphasize the word basic - are being ignored amid all the sound and fury.

Let's start with something that no one will deny: for the past few hundred years, humans have been burning larger quantities of fossil fuels than at any time in history.

Agreed? Then here is a second fact: burning fossil fuels produces carbon dioxide, which is released into the atmosphere.

And a third fact: carbon dioxide is a "greenhouse gas," whose presence in the atmosphere makes it more difficult for solar radiation to be re-radiated into space. This is less self- evident than the first two points; but no one, on either side of all the arguments, is suggesting that carbon dioxide is not a greenhouse gas.

Putting these three facts together, we have a conclusion: burning fossil fuels probably tends to increase temperatures on earth. I qualify the last statement with "probably" only because carbon dioxide released into the air may not stay there. Increased carbon dioxide leads to increased growth of vegetation, which in turn serves to reduce the level of carbon dioxide. In the long run, this could cancel out any temporary increase. However, let's go ahead with the "probable" scenario, and accept that global temperatures will tend to rise because of the increased burning of fossil fuels. Again I am hedging when I say "tend to," because there are other variables at work, such as the amount of heat provided to Earth by the Sun. The effects of solar variation might dwarf any fossil fuel burning, but let's accept the idea that such burning will be the cause of increased temperatures around the planet.

Now for consequences. When temperatures rise, other greenhouse gases such as methane tend to be released into the air. More important, some of the Earth's water stored in the form of ice will turn to liquid. As snow and ice melt and polar caps shrink, the amount of free water increases and sea levels rise. Therefore, the total area of water surface will increase as temperatures go up. Few people, if any, dispute the conclusion: global warming means higher sea levels.

However, if global temperatures rise and if the water surface area increases, then the total amount of water evaporated into the atmosphere must increase. What goes up may stay up for a while, in the form of clouds, but in the long run it must come down. The planet may have increased cloud cover, but also the total amount of water returned to the Earth as rain or snow must increase. Increased cloud cover tends to lower temperatures on the ground, because more solar radiation is reflected back into space. But if fossil fuel burning does lead to a warmer planet, it must also lead to a wetter planet.

Many discussions of global warming assert that the deserts of the Earth will increase in extent. The simple discussion provided here shows that such a conclusion runs contrary to the most elementary analysis. Although it is surely the case that with global warming some non-desert areas will become desert, on a world that is warmer and wetter this must be more than balanced by the greening of desert areas.

Now let us introduce another inarguable fact: on the land areas of our planet, there are three main reasons why some regions support little or no vegetation. Plants can not thrive where it is too dry, too high, or too cold. There is nowhere on Earth where, given adequate water supplies, it is too hot for plants to flourish, and the tropics are the places where plant life is at its most lush and abundant (and also, I have to add, where disease tends to be most virulent).

If global warming leads to a planet that is warmer, and therefore wetter, the regions where it is too cold, too high, or too dry for plants to thrive will all shrink in total area. Vegetation will flourish at higher latitudes, at higher altitudes, and in places that are currently too arid. Plant life will also grow more abundantly everywhere if the carbon dioxide level of the atmosphere increases. Thus with global warming the Earth will have a greater and more productive total area available for agriculture. It is hard to see why this should be regarded as anything but a good thing.

The groups most concerned by the prospect of global warming point to one other possibly disastrous consequence. Suppose that there is not just a "greenhouse effect," with temperatures increasing around the world, but a "runaway greenhouse effect" in which the planet becomes hotter and hotter to the point where it cannot support life of any kind. Long before such a point can be reached, two things will happen. First, increased cloud cover all around the world will lower the total amount of solar energy absorbed; second, more widespread and vigorous plant growth will reduce atmospheric carbon dioxide. The warming trend will reverse, as stored carbon released in burning fossil fuels becomes locked up again in organic life.

Conclusion: even if we accept that global warming is happening at the highest rates suggested by the most worried groups, doomsday predictions ignore logic and elementary science. In fact, global warming should lead to a world more able to sustain its increasing population.

Does this mean, then, that the world in general and the United States in particular should go on burning fossil fuels, laid down over many millions of years, as though the supply is infinite or as if future generations will have no need for such a resource?

No. Undue concern over global warming may be misguided, but the way we are burning our irreplaceable fossil fuels is worse than misguided. It's crazy.

Coming soon to this column: global cooling.

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