Mitt Romney, arguably the leading Republican candidate for president of the United States in the 2012 election, recently significantly diminished his prospects for obtaining the support he needs from the right wing of his party. How did he do this? He simply declared that he believes the Earth is warming, and that human activities are responsible. To most scientists, such a statement would be considered fairly innocuous, and an accurate assessment of current understanding. But to a large fraction of the US Republican party, this is a completely unacceptable position - ranking alongside gay marriage, gun control and abortion rights. Anthropogenic climate change has become a litmus test for Republicans in the United States.

If you want to appeal to the hard core of the party - those whom you need in order to obtain the party's nomination - you simply can not acknowledge what almost every national science academy and scientific organisation has accepted for many years. In fact, many other prominent Republicans, sensing the winds of retribution, have already back-tracked on whatever previous statements they might have made, if they contained even a whiff of climate reality. Given the importance of getting the United States on board to obtain a comprehensive international agreement on controlling greenhouse gases, this dismissal of scientific evidence about global warming is both sad and alarming.

Climate scientists on the frontlines of this battle have suffered badly from the poisonous political atmosphere. Rightwing blogs and talk radio demagogues have promoted the idea that climate science is a worthless charade, where data are simply manipulated to obtain a politically motivated result. Scientists have been abused on blogs and via emails and some have even been physically threatened. Government officials have misused their positions to intimidate and harass prominent scientists, following a strategy of attacking the messenger when they don't like hearing the message. A leading Republican senator asked the Justice Department to investigate 17 climate scientists (myself included) for committing fraud and other crimes. How have we arrived at this sorry state?

In order to understand the current state of play, one has to recognise that the issue of global warming is being completely manipulated by a group of individuals, businesses and organisations that have entrenched financial interests in making sure that the United States does not enact any legislation to control greenhouse gas emissions. At the extreme, these groups believe in complete market fundamentalism - that free markets, stripped of all constraints, will take care of any and all problems that we may face. To bolster this fundamentalist strategy, they provide major financial support to organisations that promote nonsensical ideas, such as global warming is a hoax and the IPCC reports are full of errors.

They also flood the electoral system with money, to ensure that like-minded rightwing politicians are elected to Congress. These politicians then dutifully hold hearings, inviting hand-picked scientists (often with minimal qualifications in climate science) to provide testimony which sows the seeds of doubt about the reality of global warming. The political objectives of these hearings are rarely discussed by the media. The general public just hears that more scientists disagree about an issue they find hard to deal with (which it is) and so they conclude that if scientists can't agree, why should they support legislation to control emissions? In this way, the cynical but very effective strategy of the rightwing runs its course, and the US sits on its hands while atmospheric carbon dioxide concentrations approach levels not seen on Earth for more than 2.5 million years.

If climate scientists were indeed all working together to manipulate data and create a fictitious scenario of the future, that would require a truly remarkable feat of coordination, and a sense of common purpose. What could the motivation of this cohort be? The answer was given to me by Congressman James Sensenbrenner (remarkably, now vice-chairman of the US House committee on science, space and technology). This high-ranking Republican carefully explained that the Kyoto protocol was a conspiracy by developing nations to cripple the US economy. Since these developing countries (apparently) could not compete on a level playing field with the US, they had devised the Kyoto treaty to tilt things in their direction, and climate scientists were complicit in this strategy. To those who subscribe to Sensenbrenner's bizarre idea, it is only a small step further to frame the argument in patriotic terms. If you support Kyoto (or its goals) you must be anti-American, or at the very least a socialist. Which brings me back to Mitt Romney.

The Republican party in the United States is now in thrall to the extreme right wing, which is in turn financed and coached by those with the financial muscle to promote their narrow ideological agendas. To obtain the backing of these groups, you have to toe the line, and speak the words their dogma requires: global warming is not happening, perhaps even a hoax; whatever warming has occurred is just a natural oscillation; even if humans had something to do with it, it's not a big deal and we can adapt to it. And besides, we can't afford to control greenhouse gases, as such action will result in massive job losses. For a politician seeking the party's nomination for president, it is a dangerous strategy to cross the line on this topic.

To the idealogues who have invested millions to support their political factotums in the US Congress, their money has been well spent, as meaningful legislation to control greenhouse gases has virtually disappeared from the congressional agenda. But not content with that success, they have now drawn a line in the sand for those seeking political office; global warming is off limits entirely. It is not something they want to be discussed at all.

Meanwhile, the rest of the world has recognised the reality of global warming and acknowledged the real dangers that it poses for the future. Although taking steps to address the matter is difficult, many countries have embraced the opportunity to reduce energy consumption, implement conservation strategies and promote new technologies that involve energy production from non-carbon based fuels. Politicians who embrace these strategies represent the future. Those who don't will simply become footnotes in history. Romney made the right decision - on this topic, at least.

• Raymond S Bradley is author of Global Warming and Political Intimidation, and director of the Climate System Research Center at the University of Massachusetts Amherst