SIR – David Summerfield in his letter, (April 6) supports Keith Thomson in stating that he is correct to assume that CO2 caused by human activities is causing global warming.

Unfortunately this is not so. He and many others may be convinced, but being convinced and having it proved are miles apart.

Also I am not a climate change denier as charged, but question that the change is man-made. I have yet to see unequivocal proof.

His letter follows, in general, the path of the doom-mongers, inasmuch as he threatens floods, rising sea levels, droughts and more frequent extreme weather patterns.

We have had these all before, so why make a special mention of them now? This was the direction of Al Gore, and he was completely discredited.

There is a large body of opinion which believes what David Summerfield says, but belief, conviction, extrapolated graphs, projection into the future and the like are not proof and never will be.

A G Goldsbrough, Leeds Road, Ilkley