Pachauri has said of Lomborg's new book, "Smart Solutions to Climate Change", that it "provides not only a reservoir of information on the reality of human-induced climate change, but raises vital questions and examines viable options on what can be done".

Lomborg is not one of the sceptics who denies the existence of climate change, but has argued that it is not as severe as the IPCC has said.

Now, however, his new book calls for a huge fund to tackle the problem.  "Investing $100bn annually would mean that we could essentially resolve the climate change problem by the end of this century," it says.

Lomberg's change of mind comes, for him, by adopting a free market analysis. He says he has looked at all the possible ways in which such a fund could be spent in order to get "the most bang for your buck".

With a think tank, he analysed 15 possible policies to tackle climate change which were then ranked by five economists. Taxes came near the bottom of the list. At the top was more public investment in research and development.

He said R&D would be easier to monitor than promises by politicians to cut emissions.

He compares such a fund to the massive public investment in computers from the 1950s which precipitated the commercial IT revolution. A similar low carbon revolution with massive benefits would be a result of this investment, he says.

The investment would be financed through a tax on carbon emissions that would raise $50 billion to build better sea defences, and $100 billion for global healthcare and developing clean energy sources such as wind, wave, solar and nuclear power, and more work on climate engineering such as "cloud whitening" to reflect the sun's heat back into the outer atmosphere.