In the weeks before and after the Copenhagen climate change conference last December, the science of climate change came under harsh attack by critics who contend that climate scientists have deliberately suppressed evidence — and that the science itself is severely flawed. The Intergovernmental Panel on Climate Change (IPCC), the global group of experts charged with assessing the state of climate science, has been accused of bias.

The global public is disconcerted by these attacks. If experts cannot agree that there is a climate crisis, why should governments spend billions of dollars to address it?

The fact is that the critics — who are few in number but aggressive in their attacks — are deploying tactics that they have honed for more than 25 years. During their long campaign, they have greatly exaggerated scientific disagreements in order to stop action on climate change, with special interests like Exxon Mobil footing the bill.

Many books have recently documented the games played by the climate-change deniers. Merchants of Doubt, a new book by Naomi Oreskes and Erik Conway set for release in mid-2010, will be an authoritative account of their misbehaviour. The authors show that the same group of mischief-makers, given a platform by the free-market ideologues of The Wall Street Journal's editorial page, has consistently tried to confuse the public and discredit the scientists whose insights are helping to save the world from unintended environmental harm.

Today's campaigners against action on climate change are in many cases backed by the same lobbies, individuals, and organisations that sided with the tobacco industry to discredit the science linking smoking and lung cancer. Later, they fought the scientific evidence that sulphur oxides from coal-fired power plants were causing "acid rain." Then, when it was discovered that certain chemicals called chlorofluorocarbons (CFCs) were causing the depletion of ozone in the atmosphere, the same groups launched a nasty campaign to discredit that science, too.

Later still, the group defended the tobacco giants against charges that second-hand smoke causes cancer and other diseases. And then, starting mainly in the 1980s, this same group took on the battle against climate change.

What is amazing is that, although these attacks on science have been wrong for 30 years, they still sow doubts about established facts. The truth is that there is big money backing the climate-change deniers, whether it is companies that don't want to pay the extra costs of regulation, or free-market ideologues opposed to any government controls.

The latest round of attacks involves two episodes. The first was the hacking of a climate-change research centre in England. The emails that were stolen suggested a lack of forthrightness in the presentation of some climate data. Whatever the details of this specific case, the studies in question represent a tiny fraction of the overwhelming scientific evidence that points to the reality and urgency of man-made climate change.

The second issue was a blatant error concerning glaciers that appeared in a major IPCC report. Here it should be understood that the IPCC issues thousands of pages of text. There are, no doubt, errors in those pages. But errors in the midst of a vast and complex report by the IPCC point to the inevitability of human shortcomings, not to any fundamental flaws in climate science.

When the emails and the IPCC error were brought to light, editorial writers at The Wall Street Journal launched a vicious campaign describing climate science as a hoax and a conspiracy. They claimed that scientists were fabricating evidence in order to obtain government research grants — a ludicrous accusation, I thought at the time, given that the scientists under attack have devoted their lives to finding the truth, and have certainly not become rich relative to their peers in finance and business.

But then I recalled that this line of attack — charging a scientific conspiracy to drum up "business" for science — was almost identical to that used by The Wall Street Journal and others in the past, when they fought controls on tobacco, acid rain, ozone depletion, second-hand smoke, and other dangerous pollutants. In other words, their arguments were systematic and contrived, not at all original to the circumstances.

We are witnessing a predictable process by ideologues and right-wing think tanks and publications to discredit the scientific process. Their arguments have been repeatedly disproved for 30 years — time after time — but their aggressive methods of public propaganda succeed in causing delay and confusion.

Climate change science is a wondrous intellectual activity. Great scientific minds have learned over the course of many decades to "read" the Earth's history, in order to understand how the climate system works. They have deployed brilliant physics, biology, and instrumentation (such as satellites reading detailed features of the Earth's systems) in order to advance our understanding.

And the message is clear: large-scale use of oil, coal, and gas is threatening the biology and chemistry of the planet. We are fuelling dangerous changes in Earth's climate and ocean chemistry, giving rise to extreme storms, droughts, and other hazards that will damage the food supply and the quality of life of the planet.

The IPCC and the climate scientists are telling us a crucial message. We need urgently to transform our energy, transport, food, industrial, and construction systems to reduce the dangerous human impact on the climate. It is our responsibility to listen, to understand the message, and then to act.

Copyright: Project Syndicate, 2010