The public debate over the science of climate change is being framed in a way that undermines confidence in the science system, says a senior advisor to Prime Minister John Key.
"The public is confused about what we know and what we do not know about the science, and is unsure whether governments are justified in making hard decisions, despite the science not being certain," said the PM's science advisor Sir Peter Gluckman.
"There is a growing concern among those of us who have some role in marrying science and policy that the way the debate is being framed is undermining confidence in the science system," he told a Victoria University seminar series on key policy challenges facing New Zealand.
There was a high level of denial and scepticism in the broader community, driven by a variety of motives. Comparable situations had included the arguments over tobacco and cancer, evolution and creation, and the HIV-AIDs denial movement.
He said there was "no real debate" that there was a baseline increase in global temperatures, and that the world would continue to warm for a long time even if all greenhouse emissions stopped tomorrow.
"Even in New Zealand, whose temperature is buffered by the surrounding ocean, native beech trees are already producing more seed at higher altitudes and welcome swallows are breeding noticeably earlier," he said.
But there were uncertainties over the likelihood of catastrophic flips, where large-scale melting of ice sheets or release of frozen methane could cause large and rapid climate shifts.
Sir Peter said that much of the debate in climate change was really about economic interests.
The most powerful supporter of the "so-called climate change sceptic movement" had been the fossil fuel industry.
But other deniers had included economic libertarians who believed growth was paramount, and that technology would solve any problems, and in the United States there had been a crossover with creationists where were also denying science, perhaps reflecting the idea that the world had been created for humans to exploit.
"Denialists actively confuse or convince the public and the media that the consensus is not based on sound science," said Sir Peter.
In an electronically connected world the tactics of the climate-change deniers could undermine confidence in the entire science system on which the world was increasingly dependent. Some of the responsibility lay with the media.
While the science on climate change was incomplete, the planet was degrading and the impacts of human activity were clear.
"One of those impacts is rising greenhouse gas concentrations," he said. There was an association between rising levels of gases and temperature changes, and a significant risk of an unacceptable rise in planetary temperatures.
"There is no way to test this experimentally - we only have one planet," Sir Peter said.
The most likely paths involved unacceptable temperature changes sometime in the next few decades, and some scientists thought that the rise would be faster and higher.
"Some have been arguably alarmist in taking the worst possible cases to try and get action," he said. "This is regrettable."
It was "bad science" when the appropriate response was to give ranges of temperature rise and probabilities, but to be over-optimistic about the future and minimally responsive was even more irresponsible.
"If we underestimate, then in 2050 our species might find itself facing an inhospitable future on an irreversibly degraded planet," said Sir Peter. "If we overestimate, then in 2050 we might find that we have over-invested in climate change mitigation, but most of those mitigation strategies, such as sustainable energy generation, will help to meet our other challenges."