Climate change sceptics who claim the dangers of global warming are small and far-off are "unscientific" and "irrational", and should not dissuade governments from tackling rapidly rising greenhouse gas emissions, the author of the world's landmark review of economics and climate change said.
Lord Nicolas Stern told the Guardian: "It is astonishing, irrational and unscientific to suggest the risks are small. How can they say they know the risks are small? The clear conclusion from 200 years of climate science and observations show a strong association between carbon dioxide rises and global surface temperature.
He added: "The science is unequivocal and shows there is serious danger. What is coming from [sceptics] is just noise, and should be treated as noise."
He said some sceptics were in the pay of hostile industries, with a vested interest in contradicting the science, and were being "deliberately naive" in claiming the world could wait decades to deal with rising emissions.
"It (the sceptic response) looks very well-organised," he said. "They are deliberately distorting the way we understand risk."
Stern, former chief economist at the World Bank, wrote the 2006 examination of the economics of climate change, which found that the costs of acting now on cutting emissions would be much cheaper than cutting in the future or adapting to the future effects of global warming. He has become a leading authority on climate and economics.
The world's leading climate scientists are gathered in Stockholm this week to hammer out the final details of the most comprehensive assessment to date of our knowledge of climate change. They are expected to say that it is "virtually certain" that climate change is occurring, and is mainly owing to human actions in burning fossil fuels.
They will predict that temperatures will rise by at least 2C, which is likely to cause major disruptions to the world's weather systems, including an increase in droughts, heatwaves, floods and other extreme weather in the coming decades, and sea level rises of up to a metre by 2100, which would overwhelm storm-surge defences in scores of coastal cities.
But the meeting of the Intergovernmental Panel on Climate Change has been seized on by climate sceptics, who argue that the effects of greenhouse gases will be small and felt long into the future. An estimate that 97% of the effects of carbon dioxide so far have been absorbed by the oceans has led some sceptics to claim that further warming could be similarly absorbed.
Scientists strongly contest this view, saying that research shows that the extra warming from man-made CO2 will alter the world's climate systems, and the absorption of heat by the oceans has serious effects, including sea level rises. The effects of the warming on ocean currents, and thus global weather systems that depend on them, could also cause rapid changes to weather. Fluctuations in ocean systems, such as the El Nino weather system in the Pacific, are already known to drive major weather effects such as surface warming and cooling around the globe.
Stern said: "There is the danger of an abrupt change in the whole [climate] mechanism. We need to approach the issue as one of risk management."
He said many economists had misread the impacts of future warming because their risk models were not good at taking this into account. He added that the effects of any delay in reducing greenhouse gases were of key concern, because delay means greater emissions and these will continue to wreak effects on the climate system long after the gases were first poured into the atmosphere.
"If delay did not matter, then we might have time to wait (before tackling emissions) but delay is dangerous, because of the effect on higher emissions," he said. Infrastructure, such as new fossil fuel power plants, buildings and transport networks would continue to require large volumes of fossil fuels, and building such fossil-fuel dependent new infrastructure now commits the world to higher emissions for decades to come.
Stern pointed to China, which he said was "taking seriously" the threat from emissions. "China has changed," he said, adding that other governments should take note of the efforts of the world's biggest emitter of greenhouse gases.
The results of the IPCC meeting will be published on Friday. Stern said the effects on politicians around the world were likely to be "positive" as the scientific consensus that warming posed a serious problem would become clearer and governments would face pressure from their citizens to respond. He said the current IPCC, producing the first assessment of climate science since 2007, was under "less political pressure" than previous reports.
This week, world governments meeting in New York under the auspices of the United Nations will be invited by secretary-general Ban Ki-moon to a summit of heads of state and government next year, that will pave the way for crunch negotiations in Paris in 2015, intended to forge a new global agreement on cutting emissions.
Myron Ebell, of the US Competitive Enterprise Institute, told the Guardian: "Global warming, although it may become a problem some decades in the future, is not a crisis and is highly unlikely to become a crisis.
"We should be worried that the alarmist establishment continues using junk science to promote disastrous policies that will make the world much poorer and will consign poor people in poor countries to perpetual poverty."
[A tree before and after climate change on Shutterstock]