LONDON -- Huge gales have been sweeping Britain, while temperatures have soared, leaving spring plants sprouting long before they should and wildlife bewildered. Its all part of global warming -- or so many people assert. Whether they are right will be impossible to judge for many years to come. Maybe we are indeed seeing the first uncomfortable results of generations of pouring greenhouse gases into the atmosphere. Maybe it is all part of a temporary blip, or a cycle, in weather patterns of the kind that has existed many times before in history. It is hard to tell.

All that can be said with certainty is that people the world over are now getting worried. Trend or no trend, the violent weather patterns of recent times give the world a taste of what might happen if global warming really gets a grip and the carbon content in the atmosphere reaches the fatal 550 parts per million -- at which point it is believed the weather will turn impossibly ferocious, the seas will rise, and floods and droughts will destroy our civilization.

These fears are understandable and it is right that, at the very least, humankind should take out prudent insurance in case the forecasts should turn out to be right. If we can pay a small premium now in changing lifestyles and limiting carbon emissions, that seems a reasonable line to take.

But as with all concerns about the future, this one is also taking on a less reasonable -- some would even say truly mad -- tinge. The latest fad is for everyone to go round trying to offset their carbon-emitting activities by paying for some activity or action that will somehow compensate for their environmental sins. Their "guilt" in traveling by air will somehow be expunged by paying for carbon-saving actions elsewhere.

Thus air travelers are being encouraged to pay out cash to certain bodies that promise to buy and plant a few trees to drink up -- when they have grown -- the carbon generated by the air flight. Alternatively, the promise is to spend the money on low-carbon technology projects for developing countries.

A moment's reflection will show how such ideas have shaky foundations. First, carbon emissions from aviation are only a tiny fraction of total global emissions, well less than 3 percent. Emissions from agriculture round the world are far greater and no one is proposing to tax or compensate for those. This small percentage has to be compared with a 10 percent contribution from ground transport to global warming, 24 percent from electricity generation and 18 percent from deforestation (at least half of it from destruction of the rain forests in Brazil and Indonesia).

This assumes that account can be taken of all carbon emissions from all flights worldwide. But, of course, thousands of flights take place daily with no check on their carbon "footprint," so the offsetting activity could probably only apply to flights in the advanced world or long-haul flights between world capitals and major airport hubs.

Second, since people will carry on flying anyway, in increasing numbers, the reduction in total flights will be minimal, as will the reduction in carbon emitted by them.

Third, even if less flights were booked and fewer aircraft flew, a reduction in aviation emissions would have scarcely any significant global impact -- and China's weekly emissions from coal burning probably exceed a year of carbon emissions from flying.

Fourth, the belief that planting a few trees would make good for greenhouse gas output from aircraft engines is a fantasy. To soak up one passenger's carbon emissions from, say, a London-Tokyo flight, would require a fully grown forest. A whole plane load of passengers would need to see thousands of hectares of forest planted and growing to match the carbon pumped out by their flight.

Fifth, the organizations that receive cash from "guilty flyers" and seek to put it to use in carbon-saving activities cannot guarantee that this is what will happen. They may be quite sincere in their efforts, but the results may lie decades ahead, as with tree planting. Just who will be around to check them?

Sixth, the businesses being entrusted with people's "guilt" money may be quite sincere, or they may be corner-cutters and over-persuasive sales folk, trading on people's consciences. No real accountability exists, although the British government has issued some standards that it optimistically hopes will be observed by companies offering to "offset."

All in all, the faith that air travelers are putting in such practices seems almost certain to be betrayed. There are faint similarities with the "indulgences" once so widely offered by the medieval Christian Church, which, when purchased, could save the buyer's soul -- so he or she was told to believe -- and lift the burden of wrong-doing.

The only realistic path to reduced greenhouse gas emissions and checking climate change is via far greater technical efficiency in fuel burning, and far cleaner and lighter engines in aircraft made of much lighter materials.

So the best policy would be neither to tax air travel nor to encourage moral pressure on travelers to make what are theoretically offsetting but in practice useless payments. It would be to use every device of finance, tax and government research support (some of it through military procurement of advanced flight technology) to bring on much faster the new generation of super-fuel-efficient aircraft that are already being built and to scrap the older machines that fly in large numbers, polluting as they go.

That would make a real, although small, impact. Urging nervous passengers to pay out extra cash in order to feel good about global warming will have no impact at all.