By Lesley Curwen
One Planet, BBC World Service
In Fort Worth, Texas, protesters gather at a big petrol station at the intersection of two busy highways operated by oil giant Exxon Mobil.
Mobil's garages are frequently the targets of protestors
They accuse the company of spreading doubt and "junk science" about climate change to protect its own commercial interests.
But concern about the approach of Exxon Mobil has come not just from environmental pressure groups, but from bands of scientists, including the 350-year-old Royal Society in Britain, which last September sent a letter of protest to Exxon Mobil.
"We had obtained information that they were funding groups which were distributing and publicising scientific information about climate change which we regard as misleading," says its vice president, Professor Sir David Wallace.
"It was misleading about our understanding of science, and the misleading of science is something Royal Society has an obligation to speak out for."
Keeping debate alive
The science at issue is whether it is the human race which is responsible for warming the atmosphere.
The influential UN body, the Intergovernmental Panel on Climate Change (IPCC), says this is 90% certain, and next week it will recommend policies to address that warming.
But other scientific opinion backs the argument that much of the warming happens because of natural cycles, not greenhouse gases.
And Exxon Mobil has been accused of backing groups that support the minority opinion, against what is seen as the main consensus. It confirms it backs the Heartland Institute, for example, which describes global warming science as a "fraud."
In 2005 Exxon Mobil's chairman and chief executive, Rex Tillerson defended funding such groups.
"We're going to continue to support groups that we think have good scientists involved," he said.
"The fact that they take a contrary view I don't view to be bad."
This attitude has strong backing from Richard Lindzen, Professor of Meteorology at the Massachusetts Institute of Technology, who describes Exxon Mobil as "the only principled oil and gas company I know in the US."
"They have a CEO who is not going to be bamboozled by nonsense," he adds.
Professor Lindzen wants the debate on global warming kept alive. He also describes the Royal Society letter as a "disgrace," adding "they don't know what they're talking about."
Further allegations against Exxon Mobil focused on Washington DC, where critics claim the company exercised undue influence on White House policy.
Rick Pilz, who worked for the US Climate Change Science Program, and whose job it was to oversee the writing of reports for policymakers, claimed that he saw the science watered down and censored by a White House aide.
More acres of corn have been planted than any year since 1944
"It had seemed that they were proceeding from their political position and intervening in the communication of the science itself," he says.
"This was not just an honest disagreement about policy. It was an abuse of science... the Bush administration were very closely tied to a political clientele within the major energy interests."
Eventually, in 2005, Rick Pilz decided to resign and took evidence of the alleged tampering to the New York Times.
TV ads in the US, which describe Exxon Mobil's efforts to reduce carbon emissions, suggest the company's attitude has been softening; its corporate website has climate change as an issue on the home page.
"The increase in temperatures is a risk - and a risk that needs to be addressed," says Ken Cohen, the company's vice-president, public affairs.
"As the IPCC's scenarios indicate, if this rise in temperature continues without mitigation, there will be serious impacts. Are there actions that we can take, technologies that can be applied that will somehow reduce that risk?"
Biofuel processing has strong backing from the White House
"Certainly, man's use of fossil fuels, land use changes, all contribute to the increase in CO2 emissions. Action should be based on how we lower the greenhouse gas emissions from man's activities."
He also points out that in 2005, Exxon Mobil decided to stop funding a "handful" of groups that were "focused not on the science, but on the policies."
He disassociated the company from The Heartland Institute's "fraud" claim, saying "we disagree with that statement."
Corporate money does, of course, play a huge role in America's political sphere.
Another playing the game is the bio-fuels industry. Thanks to increasing pressure to reduce carbon emissions and cut the use of foreign oil, biofuels - renewable, home-grown and marketed as less damaging than fossil fuels - have used corporate and political clout to win billions in subsidies from the US taxpayer.
Farmers in corn-growing states like Iowa and Kansas have benefited from the boom, seeing a doubling of the corn price in less than a year.
But all of this is despite serious scientific concerns about biofuels, especially corn ethanol - whose production requires lots of land, and consumes lots of energy - some say more than the fuel itself produces.
Professor Tad Patzek of the University of Berkeley in California - who says biofuel will "never produce volumes sufficient to satisfy our thirst for fuels", and adds they "severely" damage the environment, argues scientists are being used as a tool to justify government backing.
Biofuels are now powering the US Indycar series
"In doing so, they damage the reputation, and the good standing in society, of science," he says.
He also says that being a minority voice has affected his funding - and that this happens to other scientists too.
"You can clearly see a distinction between scientists who are going along with what agribusiness thinks is correct and appropriate, and those who don't," he adds.
"The scientists who toe the line receive funding, go to attractive conferences, and are treated very well - but if anyone speaks out, just once, the consequences are very severe... they don't lose their job, but they lose their funding, and it's somewhat more difficult to publish your papers."
The same charge is made by scientists who are in the minority in the climate change debate - such as Professor Richard Lindzen of MIT.
"I think there's every attempt to shut down debate," he says.
"There are plenty of people staking their economic futures on this. If the issue goes away, they're in trouble."