FOR my sins I am scientist, admittedly not a climate scientist but a geologist, and I despair when I see letters such as that from Ian McNeish (February 20). The basic thesis of his letter is that anthropogenic climate change is a fallacy, unfortunately one supported by 97 per cent of the world's scientists. As one of the 97 per cent I can agree with Mr McNeish, that the earth's climate has been constantly changing, the geological evidence is overwhelming, but after that we depart company.

I am hesitant to criticise a non-scientist with an interest in a science but the high numbers of factual errors in his short letter calls into question the depth of his scientific understanding. He both understates the age of the earth by 3,600 million years as well as the length of time that we have been keeping climate records by about 70 years. More significantly, he ignores the excellent ice core record for CO2 and temperature levels which go back 800,000 years, except to obliquely refer to the pseudo-fact that 325,000 years ago CO2 levels were higher than today. For the record, reliable and repeatable ice core data show that at 325,000 years CO2was far lower at about 265ppm whereas at present day it is around 399ppm.

Nonetheless, as a scientist, I am all too aware that evidence of correlation of CO2 levels with temperature is not in itself evidence of causation, but in the case of climate change the greenhouse mechanism by which increased CO2 may be linked to increased temperature is well understood. Given that CO2 levels are rising to levels unknown for geological millennia and at rates far higher than previously interpreted, then if nothing else, even if you were dubious about the mechanism, the reasonable person might take the precautionary view that reducing CO2 emissions is a good thing. To take a contrary view implies a wilful desire to do so and I can only wonder at the non-scientific reasons that climate change deniers have for doing this.

Bob Downie,

66 Mansewood Road, Glasgow.

IAN McNeish boldly asserts that "there is not one scintilla of scientific evidence that relates rises or falls in global temperatures to the activity of people'". If by this he means recent climate change is natural and within the realms of the Milankovitch cycles then he is wrong.

The greenhouse effect was discovered in 1824 by Fourier, the heat-trapping properties of CO2 and other gases were first measured by Tyndall in 1859, the climate sensitivity to CO2 was first computed in 1896 by Arrhenius, and by the 1950s the scientific foundations were pretty much understood. The following aspects of climate change are scientific fact: the concentration of carbon dioxide in the atmosphere is increasing more rapidly than in the last 3000 years, carbon dioxide is a greenhouse gas, carbon dioxide persists in the atmosphere for a very long time, recent climate change is not due to solar activity, climate change is not due to volcanic eruptions. Any scientist, or any individual of an inquisitive bent, with a passing acquaintance of thermodynamics, is therefore bound to ask – if the CO2 build-up on Earth is not associated with changes in the Sun's output, or the Earth's core, what is causing it? The first and second laws of thermodynamics have to be satisfied, and the only rational answer is that the source is "ancient sunlight" released by the burning of fossil fuels. While the direct heat released into the atmosphere from homes, power stations, factories and vehicles is negligible the added carbon from ancient forests is not. The thermal blanket which we are wrapping around the globe is resulting in planetary warming, which is cogently explained by quantum mechanics.

What is unknown, or difficult to predict, as the Fifth Working Report of the Intergovernmental Panel on Climate Change makes perfectly clear, is how warm it will get and how quickly.

Any discussion that remains revolves around the transition, which the human race must make, to achieve a fossil fuel free mode of existence, so that future generations of humans are bequeathed a habitable planet. The available evidence points to a wholesale adoption of renewable energy sources, backed by massive energy storage techniques, as probably the most effective route forward.

Alan J Sangster,

37 Craigmount Terrace,

Edinburgh.