Published: January 22 2001 19:33GMT | Last Updated: January 22 2001 19:40GMT Nobody can be sure about a weather forecast that looks 100 years ahead, even if it comes from 123 experts assembled by the Intergovernmental Panel on Climate Change. In its latest warning, the IPCC suggests that global temperatures may rise by between 1.40 C and 5.80 C by 2010, a significantly bigger increase than it expected five years ago. But there are big uncertainties behind the computer programs that generate such scenarios - in both the science of climate change and the assumptions that must be made about economic and population growth. So the IPCC's experts should avoid decimal points that suggest a spurious precision. All they can really say is that the earth is getting warmer and that this is likely to continue at what seems to be an accelerating rate. Even this expectation must be set against big natural changes over the last millennium. In its 1995 report the IPCC said that in the 13th century the world had been very much warmer than it was at the time of the report and in the 16th century it had been very much colder. Compared with such variations, the temperature rise since the cold period in the middle of this century has been fairly modest. Yet despite these big uncertainties, the IPCC's warning must be taken seriously. Even allowing for special factors such as the El Nino Pacific current, the temperature was rising fast in the 1990s. In 1995, the experts said that human activity might be having some "discernible influence" on the global climate. Now they think that this is likely. If their worst fears were to be realised, the world would face a calamity of huge proportions. To avert the threat of flooding, tempests and droughts, a significant proportion of economic growth would have to be sacrificed over many decades to control greenhouse gas emissions. But even the relatively modest measures now being proposed are proving unpopular - as was shown by the collapse of the summit at The Hague in November. Industries do not want to sacrifice their competitiveness and consumers do not want higher fuel prices. The idea that a switch to nuclear power may be needed to control carbon emissions is disliked even more. Meanwhile some sceptics argue that it would be wrong to take expensive measures now that might turn out to be ineffective or even unnecessary. The world's political leaders must try to overcome these objections when they resume their discussions in Bonn in Germany in May. Progress may be slower than many European governments would like, particularly after the switch to a Republican administration in the US. Compromises will be needed but an international consensus must be rebuilt. The uncertainties are great - but so are the dangers. _______________________________________________ Crashlist website: http://website.lineone.net/~resource_base
