The "father of climate change" has a stark message for those proposing to mine fossil fuels in New Zealand: "Leave the coal in the ground."
James Hansen, the first scientist to bring global warming to the world's attention in testimony to the United States Congress, is in the country for a series of public talks.
After deciding that an individual scientist could not compete with the influence of fossil fuel companies, Dr Hansen has turned to activism. Much of his criticism focuses on the hypocrisy of governments - which talk green but have few green policies - and the dangers of coal-burning.
Dr Hansen said these problems were relevant to New Zealand.
"This is a beautiful country, but there are some inconsistencies. Pretending to be green, having this pure image, while looking to mine lignite ... is as bad as it gets."
Dr Hansen has just co-written a paper which says emissions reductions of 6 to 7 per cent are needed each year to avoid harmful imbalances in the atmosphere.
If companies continued to dig for every last bit of coal, oil, and gas, this goal was impossible, he said.
"As long as fossil fuels are the cheapest energy, we will continue to burn them. That is as certain as the law of gravity.
"The reason that they are the cheapest is because they are not made to pay for their cost to society - around one million deaths a year from air and water pollution, mostly from fossil fuels."
He proposes a "simple, honest, across-the-board" carbon tax, in which the revenue returns to the public as a dividend.
He said cap-and-trade schemes overseas had been engineered to favour big business.
Here, a Consumer NZ study has found that taxpayers, not big polluters, will bear the brunt of the Emissions Trading Scheme.
"The money collected should be distributed on a per capita basis, because then the person who does better than average in limiting their fossil fuels will actually make money."
Dr Hansen said that if the tax was increased sharply, dependence on fossil fuels would become unsustainable, and cleaner energies would push into the market.
"The prescription is simple. It is what we need to do if we are to solve the climate problem."
During his visit the Nasa director will attend a symposium on coal in Wellington, and also visit the site of proposed lignite developments in Southland.
While he has been criticised as an alarmist, Dr Hansen says the matter of cutting emissions is one of great urgency. If no progress is made in the next decade, he believes that governments will have to introduce highly expensive geo-engineering.
DR JAMES HANSEN
* Age: 70.
* Director of Nasa's Goddard Institute for Space Studies.
* Adjunct Professor at Columbia University's Earth Institute.
* First scientist to publicly draw attention to global warming.
* Developed pioneering models of Earth's climate in 1980s.
* Arrested twice for anti-mining protests.
* Strongly against coal but pro-nuclear for India and China.
"Coal is the single greatest threat to civilisation and all life on our planet."
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