SIR – David Somerville (Letters, April 6) states that the overwhelming majority of scientists who work in the field of climatology are convinced “that global warming is caused by CO2 and other greenhouse gases produced by human activities”.

When I went to school, conclusions on scientific matters were not subject to a majority vote. I remember something about beginning with a hypothesis, finding evidence, testing the evidence, and looking for events which might disprove the hypothesis. Scientists are always ready to revise their conclusions in the light of new evidence.

The unstated assumption in Mr Somerville’s letter is that there is such a thing as global warming, or rather, that any global warming that may be happening differs in kind from previous examples in the history of the earth. What proof is there of this? We’re talking about science here.

In any case, I am far from convinced that even the above statement by Mr Somerville is factually true: there have been some very underhand tactics going on in this field, such as would put even politicians to shame. Is there an electoral roll of climate scientists?

A Michael Murphy, Baildon Wood Court, Baildon