KEY POINTS:
The biggest "environmental" issue in Britain for the past year has been the plan to build a third runway at London's Heathrow airport.
The growth of air travel, the protesters claim, is a major cause of global warming, and John Sauven, director of Greenpeace UK, predicted that Heathrow would become "the battlefield of our generation." So the protesters contacted Jim Hansen, one of the world's leading climate scientists, to back them their campaign.
They assumed that Hansen, the director of Nasa's Goddard Institute for Space Studies in New York, would back their campaign, for last year he helped to defend six British protesters charged with criminal damage after occupying a coal-fired power station in Kent. To the obvious astonishment of the Heathrow protesters, he refused.
Hansen resisted several attempts by President Bush to silence him during the Great Darkness, and recently wrote an open letter to Barack Obama warning him that he must act decisively on climate change in his first term. Nor does he deny that planes flying through the stratosphere contribute to global warming.
He just insists on a sense of proportion - and he does not think that devoting the energies of the entire British environmental movement to preventing a third runway at Heathrow is a productive use of its time.
"Coal is 80 per cent of the planet's problems," he said in an interview with the Observer.
All fossil fuels are a problem, for they all release carbon dioxide that was buried underground long ago back into the atmosphere, but coal is by far the worst. A coal-fired generating plant emits twice as much carbon dioxide as a gas-fired plant that produces the same amount of electricity.
That is where the big cuts must be made soon if we are to escape grave consequences, and going after aviation emissions now is only a fashionable distraction. So why do people do it? For the same reason that they think that changing the kind of light-bulbs they use and driving more fuel-efficient cars will save us from really destructive climate change. Those are bite-sized chunks of the problem that seem relatively easy to tackle, whereas the real work of changing the way the human race generates its energy seems too big to contemplate. Especially since so-called "clean coal" is probably a mirage.
The technology for capturing and burying the carbon dioxide produced by burning coal does exist, but it has never been tested at one-hundredth of the scale needed to cope with the emissions of a typical 500-megawatt power station. Why? Maybe because the coal industry secretly suspects that the economics of the operation would be prohibitive, and would rather not know for sure.
But after we have stopped burning coal and gas to generate electricity, and after we have even replaced oil for most purposes, we will eventually have to deal with aviation's contribution to global warming, for by then it will constitute a significant part of the remaining problem.
Happily, there is a solution. The major problem with airliners is not the carbon dioxide they produce as they fly - and in any case, that can be solved just by substituting some bio-fuel with a high enough energy content. Several such fuels are being experimented with now, and will very likely be commercially available in 10 or 15 years.
The real issue - three or four times bigger than the CO2 problem, by most estimates - is the water vapour that high-flying airliners dump into the stratosphere, which turns into persistent high-altitude clouds that reflect heat back to the surface and contribute to global warming.
The solution to that, obviously, is to fly lower than 27,000 feet (8000m), down in the weather, where the water vapour turns harmlessly into rain. But that means smaller wings, because the air is denser down there, and smaller wings mean longer takeoff and landing runs. Flying in the troposphere also means constant turbulence and a lot of air-sickness bags. But there is a single technology that would solve all of these problems at once.
"If you go to something called circulation control," explains Dennis Bushnell, the chief scientist at Nasa's Langley Research Centre, "which is to bleed the engines and inject air backwards at the upper trailing edge of the wing, you can produce lift coefficients which are easily three or four times what we can get out of conventional wings."
That means very short takeoffs and landings, so short that existing runways could accommodate several aircraft at once. And the same circulation control system, used in flight, has "such tremendous control authority" that it can counter the bumps that are normally part of flying down in the weather and produce a smooth ride.
Problem solved - in 15 or 20 years, when that technology is incorporated into the civil airliner fleet and aviation-grade biofuels are available. Even Heathrow's third-runway problem would be solved at that point, since far more aircraft could use the existing two.
Climate change is a problem caused by technology, and most of the potential solutions are also technological. Aviation is a small part of the problem, and the solutions will be along in a while. Concentrate on closing down the coal-fired power stations, and we may get through this without too many casualties.
* Gwynne Dyer's new book, Climate Wars, is published in New Zealand by Scribe.
