I will certainly admit to being one of those unconvinced by the claims that we are undergoing catastrophic warming. It is the case, as Paul Shaw says (Letters, November 29), that some glaciers are melting. It is also the case that some are growing and some just sitting there. That there are currently glaciers in the Alps blocking places which, in Roman times, were used as passes, means that even the glacier evidence shows nothing outwith historical experience.

The major recent piece of evidence, which sadly has gone unreported by the British media, is that it has recently been proven that US records purporting to show current extreme warming were wrong. They were distorted by the fact that recording stations, which, a century ago were in open countryside, are now deep inside cities (in one case beside the outlet for a factory's air-conditioning system). The corrected US figures now show 1934 was the warmest year on record and four of the 10 warmest were in the 1930s. To be fair, this error has not been accepted by other countries but since the fullest records were kept by the US, and an even higher proportion of urban records, this is difficult seriously to deny.

Sir David King, a political appointee, is on record as having said that by the end of this century Antarctica will be "the only habitable continent", implying a temperature rise of more than 30 degrees and has subsequently, in what the BBC reported as his "strongest warning yet", said it would be three degrees. He may not be the ultimate authority.

I pointed out in my previous letter that there have been several periods in history when global temperature was significantly warmer than now (middle ages up to 1350, late Roman and pre-5000BC). These were uniformly periods of prosperity, looked back on as golden ages. Mr Shaw did not dispute this.

The late H L Mencken said: "The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary." I regard the current global warming scare and, indeed, the previous global ice-age scare of the 1970s and early 1980s, among many others, as being such hobgoblins pushed by a Luddite environmentalist movement trying to justify its existence and governments trying to justify higher taxes and more regulation.

Neil Craig, 200 Woodlands Road, Glasgow.

The letter from Helen McDade contained a lot of good sense about energy conservation and generation. It was a pity that the small paragraph telling of Greenpeace's latest attack on nuclear power - that it needs a subsidy - did not include a reply from someone who knows the facts. Information which is available from many leading industrial nations makes it clear that building new nuclear power stations, although capital intensive (just as wind farms are), is the most economic way to generate electricity. Any doubters should read some of the reports published by the OECD.

G I Crawford, 10 Gailes Park, Bothwell.

Paul Shaw (November 29) says that Sir David King's statement about the weight of evidence refutes Neil Craig's allegation on earlier examples of warming. Weight of evidence has often been wrong in the past. Had that been valid, the Earth would still be flat and the sun would be in orbit around the Earth. These were almost universally-held views at one time. The answers in physics have always been a critical experiment that is unequivocal in its result.

Weight of evidence implies that is the majority feeling, but it also implies that there are minority views, and historically these have been held by such as Galileo and Copernicus. An important question in weighing evidence is whether the majority or the minority is right.

Paul Shaw cites the increasing liberation of methane in Siberia. Ian Stewart's current TV series on geology points out that the increasing temperature is liberating Siberian methane, that is alleged to be many times more potent as a greenhouse gas than carbon dioxide. A short time ago in geological terms, about 7000 years, Siberia was warm enough to support mammoths and their nutritional vegetation. The methane there is much older, several million years, and we must assume some of that was liberated, but the Earth seemed to survive without catastrophe. Only 600 years ago, Greenland was warm enough for farming.

The medieval warm period and the little ice age are well attested and appear in the 1990 IPCC report. The medieval warm period was about 2C above today's temperature, and the little ice age about 2C colder. Even today, with our highly sophisticated measurement laboratories, the mean global temperature, which is what causes much argument, is very difficult to measure. It has to average day and night, tropical and polar, temperatures, and that is far from easy. To that end, Tiros (television infra-red observation satellite) was launched in 1960. That is supposed to measure mean temperature, but the results are somewhat inconclusive, yet it has been reported that there has been very little temperature change over the past few decades. I am not sure of the physics of Tiros so cannot comment on the validity of its measurements, although they did claim to detect the 1998 el nino peak.

Chris Parton, 40 Bellshill Road, Uddingston.