A top environment lawyer says it is time to stop watching opinion polls and get on with doing something about climate change.

Dr Klaus Bosselmann, director of the New Zealand Centre for Environmental Law at Auckland University, said opinion polls were fickle and not linked to scientific evidence, whereas Government decisions should be based on fact.

He was responding to a Nielsen poll of 2296 people reported in the Green Pages last week which found about one in five thought global warming was a giant con and a further 28 per cent that it had not been proven.

Dr Bosselmann, who has been involved in climate change politics for 20 years and was a German government delegate at 1992 climate talks, said the poll was consistent with a worldwide trend of declining belief in global warming in 2008 and 2009.

He believed that if the same poll had been taken 20 years ago it would have shown higher levels of belief - although the science supporting man-made global warming was stronger today.

The apparent decline in public certainty about climate change has prompted soul-searching among scientists, some of whom blamed media reports for giving undue emphasis to climate-change doubters.

Peter Griffin of the Science Media Centre, a Government-funded communication hub between scientists and journalists, said drama and controversy was always going to be more compelling to people than the "fairly dry" facts. But he said public views could not be ignored.

"It is unacceptable to say that buy-in from the public isn't needed.

"If the overwhelming majority of the public isn't satisfied that the science indicates a need to act ... the political will dissipates too."

Dr Bosselmann said the science had firmed up an unbelievable amount in the past two decades.

But "public opinion in New Zealand changes fairly quickly", he said. "One big news [item] affects pretty much everybody."

Terry Dunleavy, secretary of a group questioning man-made global warming, the New Zealand Climate Science Coalition, said people had grown more sceptical when faced with having to pay money to curb greenhouse gases.

Also: "What has turned the majority of people in the Western world into climate sceptics has been their own observation that climate is not doing what the IPCC, etc predicted," he said.

Mr Dunleavy said temperatures had not increased this century despite increasing greenhouse gases.

Despite the doubters, climate scientists say temperatures are tracking in line with IPCC predictions for a background trend of warming, peppered with dips and troughs caused by other factors.

Niwa records for New Zealand show the 2000s were the hottest decade on record, although only fractionally hotter than 1980s.

Mr Griffin said the Climategate emails taken from the University of East Anglia and the recent IPCC gaffe over the Himalayan glaciers had done "a huge amount of damage to the reputation of climate science".

The emails, published online shortly before the Copenhagen climate talks, showed top climate experts trying to avoid releasing data to their critics.

Then the IPCC was forced to express regret last week after exaggerated claims about the melt-rate of Himalayan glaciers appeared in a report, despite not having been published in a peer-reviewed journal.

The Prime Minister's science adviser told the Herald last week that, while there would always be maverick results, they were few compared with the weight of evidence for man-made global warming.

Mr Griffin said that neither the East Anglia nor Himalayan scandals changed the overwhelming evidence suggesting that humans were contributing in a significant way to climate change.

But he said climate science was as complex as it got, which made it a hard sell.