They are either championed as brave voices willing to speak out against the scientific majority or dismissed as cranks who lack the evidence to support their arguments.

Now deniers of global warming have been dealt a stinging blow by psychologists who found skeptics of man-made climate change tend to believe in conspiracy theories.

They say the conspiracist outlook taken by many climate change skeptics is harming the public debate over global warming.

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Bloggers who deny human activities, such as the burning of fossil fuels above, are causing climate change will often use language that suggests they believe in conspiracy theories, a new scientific paper has claimed

The researchers studied the response to a previous study looking at the role conspiracy theories play in online blogs that deny the scientific consensus on climate change.

They found around a fifth of the comments about the research 'can be considered conspiracist'.

It builds on a previous survey that the researchers conducted, which found up to 40 per cent of those who are skeptical about global warming use imagery that invoked conspiracy theories.

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This includes the use of words like 'scam' and repeated references to faked data and collusion between scientists and governments to deliberately conceal evidence.

Professor Stephan Lewandowsky, an experimental psychologist at the University of Bristol who led the work, said: 'These results add to a growing body of research on the nature of internet discourse and the role of the blogosphere in climate denial.

'It also confirms that conspiratorial elements are readily identifiable in blogosphere discourse'

The paper, which is published in the Journal of Social and Political Psychology, provides a damning view of skeptical bloggers and those who comment on their websites.

The term 'conspiracy theory' is often used as a way of dismissing and ridiculing a person's beliefs.

Well known conspiracies include claims that the existence of alien life has been covered up and that the Moon landings were faked.

The majority of scientists deny there is a conspiracy to paint climate change as worse than it is and Prince Charles, who campaigns on environmental issues, recently insisted there was no such conspiracy.

He said the international bodies that now accept the threat of climate change could 'scarcely be accused of being part of some half-baked conspiracy dreamt up by extreme environmentalists intent on undermining capitalism'.

This graph shows how global temperatures have changed since 1880. The so called 'pause' in global warming seen on the right since the early 2000s has been seized upon by many skeptics as proof that manmade climate change is a myth or at least not happening at rates predicted by the models used by climate scientists

However, there are some high profile critics of climate science who insist there are attempts to silence critics of climate science.

Former Chancellor Lord Lawson, for example, has accused the BBC of banning him from debating the topic.

The new research confirms that there is a strong feeling among climate change skeptics that there is a conspiracy of some sort surrounding global warming science.

However, critics of the paper will point out that the authors themselves have received intense criticism from climate change deniers for their previous research that has painted skeptics as conspiracy theorists.

Their earlier study, published in 2012 and titled Recursive Fury, received multiple complaints and Professor Lewandowsky claims there were attempts to block its publication and have it retracted.

It was eventually retracted by the journal that published it for 'legal' reasons but it insisted there were not ethical or academic issues with the study.

Their latest paper, published in a different journal, is seen as a response to this criticism and examines the blog posts about the previous study.

The Apollo Moon landings by Neil Armstrong and Buzz Aldrin in 1969 is surrounded conspiracy theories that claim the major event in human history did not happen and was faked here on Earth

They also gave 'naive' students material from skeptics blogs and asked them to assess them for conspiracy theories and scholarship.

These were compared to scientifically compared critiques. The researchers say the blog posts tended to be high in conspiracism but low on scholarship.

Writing in the journal, the researchers said: 'On numerous blogs, it appeared to be taken for granted that the data was "faked" or "scammed".

'In one blog post that repeated the words "scam" or "scammed" 21 times, the author asserted that "almost certainly" some respondents of the survey were caricaturing climate "skeptics".

'Indeed, most of the hypotheses advanced about LOG12 (the Recursive Fury paper published in 2012) included an accusation of intentional wrong-doing by the authors, which goes beyond pointing to problems and errors as would be the norm in conventional scientific discourse.

'The ease with which those presumptions about misconduct and malfeasance were made and accepted provides a fertile environment in the blogosphere for the subsequent unfolding of conspiracist ideation.'

They also warn that some extreme climate change deniers have also resorted to 'harassing' scientists and the editors of journals.

Former Chancellor Lord Lawson, shown above, is a prominent skeptic of manmade climate change and has accused the BBC of banning him from debating the topic

They say the conspiracy theories put forward by many blogs written by skeptics is failing to encourage reasonable debate about climate science among the public.

They write: 'There are indications that seeking the retraction of inconvenient papers has become a routine practice among individuals who are denying (climate) science.

'To date, we have become aware of 7 instances in which editors were subject to what can reasonably be classified as harassment or intimidation in order to achieve the retraction of inconvenient papers.

'The potentially chilling effects of those activities on academic freedom must be analyzed further.

'Our results point to the need to educate the public about the difference between scientific and non-scientific forms of discourse.'

The new paper has already provoked an angry response from climate change skeptics.

Writing on the sceptical blogsite Watts Up With That, Anthony Watts dismissed the work as a 'smear'.