Sir - I am not myself a scientist, but I know well that science is based entirely on probabilities.

The force of gravity, the speed of light and so on are assumed to be facts only until proven otherwise. Even a dogmatist like Richard Dawkins bases his theory that there is no God on his belief that he can prove it beyond reasonable doubt; but because he is a responsible scientist he accepts that that doubt must exist.

When the great majority of informed scientists say that global warming is very likely to be caused by human activities, they are saying that the probability of that theory being correct is over 90 per cent certain.

Of course people like Mr Tyce (Letters, November 30) can happily go ahead and gamble on a less than one in ten chance; but most of us prefer shorter odds.

Where I have some sympathy with him is in querying whether it can ever be an adequate solution for even enormous numbers of well-meaning European and North American middle-class people to switch to long-life light bulbs and avoid flying and insulate their homes and all the rest of it, very well worthwhile as all those actions are.

What our leaders ought to be doing, surely, is making clear to the extractive industries that it is as unacceptable for them to chuck their toxic waste into the atmosphere as it is for the nuclear industry to do so. The technology exists for the oil and gas industries to extract and sequester carbon at source, and for coal-fired power stations to remove it before emitting waste. It may not be cheap, but I would have thought it a lot less costly than rendering this planet uninhabitable by the human race.

Hubert Allen, Old Marston