Weather: Taking a cool look at the threat of global warming

As the nations of the world posture before next week's Kyoto conference on climate change, the task of reaching agreement on reducing greenhouse gas emissions looks impossible. But it may not matter much - the scientific case for global warming is by no means as clearly established as some politicians think.

China - which is suspected of causing more greenhouse gas emissions than any country other than the United States - wants no binding targets on reducing fossil fuel consumption. Japan proposes that emissions be reduced, by the year 2012, by 5 per cent from 1990 levels. The European Union wants a 15 per cent reduction by 2010 - but measured over Europe as a whole, not country-by-country - and the United States want to stabilise at 1990 levels by the year 2012. Brazil has rejected suggestions that the poorer nations should also agree to limit gas emissions, and France has announced plans to cut domestic energy consumption by 7 per cent.

As the final round of posturing comes to a frenzied end before next week's world climate talks begin in Kyoto, it looks as though the delegates will be faced with a fortnight of fudge if they are to produce any agreement at the end of it. But in the fug of carbon dioxide surrounding all this politicking, we are in danger of losing sight of the basic question: Is the world really in danger?

The facts are not easy to establish. The average temperature on earth is about 0.6 degrees higher than it was a century ago - true. We are belching far more carbon dioxide and other greenhouse gases into the atmosphere than ever before - true. Such gases prevent radiated warmth escaping into space, thus causing the earth to get hotter - true ... up to a point.

Now let's go back a few years. In 1971, the journal Science reported that: "An increase by only a factor of four in global aerosol background concentration may be sufficient to reduce the surface temperature by as much as 3.5 degrees kelvin ... sufficient to trigger an ice age." In 1976, Lowell Ponte, in his book The Cooling, predicted that unless measures were taken to deal with the lowering that was taking place in the earth's temperature: "the cooling will cause world famine, world chaos, and probably world war, and this could all come by the year 2000." As recently as 1992, a survey of meteorologists and geologists showed that only 60 per cent believed that temperatures had risen over the last hundred years, and only 19 per cent thought that man-made causes were responsible.

Since then the balance of the scientific argument seems to have shifted slightly in favour of the global warming hypothesis with several studies showing a correlation between temperature change and man-made greenhouse gas emissions, but the connection is not established beyond doubt. In any case, if, as has been estimated, human action has been responsible for about a quarter of a degree rise in the earth's temperature this century, does this really make much difference when a major volcanic eruption can change the temperature by 0.2 on its own?

The argument, sadly has become one between the oil lobby and the politicians. The former want to maintain demand for their product, the latter deperately want to be seen to be behaving responsibly - as long as saving the earth is what the voters want.