A campaign is being waged against climate change science to undermine public acceptance of man-made global warming, environment experts claim.

The attack against scientists supportive of the idea of man-made climate change has grown since the leak of documents from the University of East Anglia (UEA) before the Copenhagen climate summit.

Free-market, anti-climate change think-tanks such as the Atlas Economic Research Foundation in the US and the International Policy Network in the UK have received grants totalling hundreds of thousands of pounds from the multinational energy company ExxonMobil.

Both organisations have funded international seminars pulling together climate change deniers from across the globe.

Many of these critics have broadcast material from the leaked UEA emails to undermine climate change predictions and to highlight errors in claims that the Himalayan glaciers could disappear by 2035.

Last week climate sceptic bloggers broadcast stories casting doubts on scientific data predicting dramatic loss of the Amazon rainforest.

Professor Bob Watson, chief scientific adviser to the Department for Environment, Food and Rural Affairs (Defra) in Britain and former chairman of the IPCC, said: "It does appear that there's a concerted effort by a number of sceptics to undermine the credibility of the evidence behind human-induced climate change.

"I am sure there are some sceptics who may well be funded by the private sector to try to cast uncertainty."

The Atlas Foundation, created by the late Sir Anthony Fisher (founder of the Institute of Economic Affairs), received more than US$100,000 in 2008 from ExxonMobil, according to the oil company's reports.

ExxonMobil said in a statement: "We discontinued contributions to several public policy research groups whose position on climate change could divert attention from the important discussion about how the world will secure the energy required for economic growth in an environmentally responsible manner."