A climate scientist who says he has been subjected to a vitriolic hate campaign has denounced the way that American billionaires have been able to secretly finance the climate-sceptic organisations that have attacked him.

Professor Michael Mann of Pennsylvania University, who has been targeted by climate-change sceptics for his work on global temperature records, said it was wrong for wealthy individuals such as the oil billionaire Charles Koch to surreptitiously finance the “counter-movement” that denounces the science of global warming.

Yesterday, The Independent revealed that a fund operated by the Koch family has given millions of dollars to climate-sceptic organisations though a financial intermediary “donor advised fund” called The Donors Trust. Charles Koch and his wife, Liz, are directors of the Knowledge and Progress Fund which gives money to theDonors Trust, which then passes on the funds to climate sceptic organisations.

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One such climate-change sceptic body, the Competitive Enterprise Institute, is being sued by Professor Mann for defamation relating to suggestions he committed scientific fraud and could be compared to a convicted child molester. Professor Mann said the allegations are untrue and are part of a smear campaign.

It was only when he was researching a book that he became aware Koch was assisting some of the organisations that he says have been attacking him and his colleagues for so many years, Professor Mann said. He said the sceptic organisations had “single-handedly sought to poison the public discourse over human-caused climate change. In the process they