By Richard Black
Environment correspondent, BBC News website
The Nobel-prizewinning IPCC is among the bodies that lodged complaints
A controversial Channel 4 film on global warming broke Ofcom rules, the media regulator says.
The Great Global Warming Swindle attracted various complaints, including claims that it misled contributors.
In a long-awaited judgement, Ofcom says Channel 4 did not fulfil obligations to be impartial and to reflect a range of views on controversial issues.
However, it judges that the film did not mislead audiences "so as to cause harm or offence".
Channel 4 said it aired the documentary to demonstrate that "the debate" on climate change was not over.
The Intergovernmental Panel on Climate Change (IPCC) and the former UK government chief scientific adviser Sir David King were among those whose complaints were upheld.
The film's key contention was that the increase in atmospheric temperatures observed since the 1970s was not primarily caused by emissions of greenhouse gases from burning fossil fuels.
First aired by Channel 4 in March 2007, the documentary has since reportedly been sold to 21 countries and distributed on DVD.
Among discussion groups of "climate sceptics", it is sometimes cited as a counter to Al Gore's documentary An Inconvenient Truth and has been credited with infuencing public opinion on the causes of modern-day climate change.
The regulator backed Sir David's complaint of unfair treatment, judging that his views were misrepresented and that he was not given the right to reply.
Ofcom also found in favour of Carl Wunsch, an oceanographer interviewed for the programme, who said he had been misled as to its intent.
Dr Wunsch, from the Massachussetts Institute of Technology, said he believed he was being asked to take part in a programme that would "discuss in a balanced way the complicated elements of understanding of climate change", but "what we now have is an out-and-out propaganda piece, in which there is not even a gesture toward balance".
The Broadcasting Code requires Channel 4 to show "due impartiality" on "matters of major political and industrial controversy and major matters relating to current public policy".
The last segment of the programme, dealing with the politics of climate change, broke this obligation, Ofcom judged, and did not reflect a range of views, as required under the code.
However, the regulator said it did not believe, given the nature of the programme, that this led to the audience being "materially misled so as to cause harm or offence" - the standard that Ofcom says complaints have to reach.
Ofcom's logic is that "the link between human activity and global warming... became settled before March 2007".
This being so, it says, disputing the scientific link between human activity and climate change does not meet the Broadcasting Code's definition of "controversial".
While some of the 265 complaints received by Ofcom were short and straightforward, one group assembled a 176-page document alleging 137 breaches of the Broadcasting Code.
Channel 4 will have to broadcast a summary of the Ofcom findings.