Leading climatologist explains why President Obama's administration is the last chance to avoid catastrophe.
Along one wall of Jim Hansen's wood-paneled office in upper Manhattan, the distinguished climatologist has pinned 10 A4-sized photographs of his three grandchildren: Sophie, Connor and Jake. They are the only personal items on display in an office otherwise dominated by stacks of manila folders, bundles of papers and cardboard boxes filled with reports on climate variations and atmospheric measurements.
The director of Nasa's Goddard Institute for Space Studies in New York is clearly a doting grandfather as well as an internationally revered climate scientist. Yet his pictures are more than mere expressions of familial love. They are reminders to the 67-year-old scientist of his duty to future generations, children whom he now believes are threatened by a global greenhouse catastrophe that is spiraling out of control because of soaring carbon dioxide emissions from industry and transport.
"I have been described as the grandfather of climate change. In fact, I am just a grandfather and I do not want my grandchildren to say that grandpa understood what was happening but didn't make it clear," Hansen said last week. Hence his warning to Barack Obama, who will be inaugurated as US president on Tuesday. His four-year administration offers the world a last chance to get things right, Hansen said. If it fails, global disaster - melted sea caps, flooded cities, species extinctions and spreading deserts - awaits mankind.
"We cannot now afford to put off change any longer. We have to get on a new path within this new administration. We have only four years left for Obama to set an example to the rest of the world. America must take the lead."
After eight years of opposing moves to combat climate change, thanks to the policies of President George Bush, the US had given itself no time for manoeuvre, he said. Only drastic, immediate change can save the day and those changes proposed by Hansen - who appeared in Al Gore's An Inconvenient Truth and is a winner of the World Wildlife Fund's top conservation award - are certainly far-reaching. In particular, the idea of continuing with "cap-and-trade" schemes, which allow countries to trade allowances and permits for emitting carbon dioxide, must now be scrapped, he insisted. Such schemes, encouraged by the Kyoto climate treaty, were simply "weak tea" and did not work. "The United States did not sign Kyoto, yet its emissions are not that different from the countries that did sign it."
Thus plans to include carbon trading schemes in talks about future climate agreements were a desperate error, he said. "It's just green wash. I would rather the forthcoming Copenhagen climate talks fail than we agree to a bad deal," Hansen said.
Only a carbon tax, agreed by the west and then imposed on the rest of the world through political pressure and trade tariffs, would succeed in the now-desperate task of stopping the rise of emissions, he argued. This tax would be imposed on oil corporations and gas companies and would specifically raise the prices of fuels across the globe, making their use less attractive. In addition, the mining of coal - by far the worst emitter of carbon dioxide - would be phased out entirely along with coal-burning power plants which he called factories of death.
"Coal is responsible for as much atmospheric carbon dioxide as other fossil fuels combined and it still has far greater reserves. We must stop using it." Instead, programs for building wind, solar and other renewable energy plants should be given major boosts, along with research programs for new generations of nuclear reactors.
Hansen's strident calls for action stem from his special view of our changing world. He and his staff monitor temperatures relayed to the institute - an anonymous brownstone near Columbia University - from thousands of sites around the world, including satellites and bases in Antarctica. These have revealed that our planet has gone through a 0.6C rise in temperature since 1970, with the 10 hottest years having occurred between 1997 and 2008: unambiguous evidence, he believes, that Earth is beginning to overheat dangerously.
Last week, however, Hansen revealed his findings for 2008 which show, surprisingly, that last year was the coolest this century, although still hot by standards of the 20th century. The finding will doubtless be seized on by climate change deniers, for whom Hansen is a particular hate figure, and used as "evidence" that global warming is a hoax.
However, deniers should show caution, Hansen insisted: most of the planet was exceptionally warm last year. Only a strong La Niña - a vast cooling of the Pacific that occurs every few years - brought down the average temperature. La Niña would not persist, he said. "Before the end of Obama's first term, we will be seeing new record temperatures. I can promise the president that."
Hansen's uncompromising views are, in some ways, unusual. Apart from his senior Nasa post, he holds a professorship in environmental sciences at Columbia and dresses like a tweedy academic: green jumper with elbow pads, cords and check cotton shirt. Yet behind his unassuming, self-effacing manner, the former planetary scientist has shown surprising steel throughout his career. In 1988, he electrified a congressional hearing, on a particular hot, sticky day in June, when he announced he was "99% certain" that global warming was to blame for the weather and that the planet was now in peril from rising carbon dioxide emissions. His remarks, which made headlines across the US, pushed global warming on to news agendas for the first time.
Over the years, Hansen persisted with his warnings. Then, in 2005, he gave a talk at the American Geophysical Union in which he argued that the year was the warmest on record and that industrial carbon emissions were to blame. A furious White House phoned Nasa and Hansen was banned from appearing in newspapers or on television or radio. It was a bungled attempt at censorship. Newspapers revealed that Hansen was being silenced and his story, along with his warnings about the climate, got global coverage.
Since then Hansen has continued his mission "to make clear" the dangers of climate change, sending a letter last December from himself and his wife Anniek about the urgency of the planet's climatic peril to Barack and Michelle Obama. "We decided to send it to both of them because we thought there may be a better chance she will think about this or have time for it. The difficulty of this problem [of global warming] is that its main impacts will be felt by our children and by our grandchildren. A mother tends to be concerned about such things."
Nor have his messages of imminent doom been restricted to US politicians. The heads of the governments of Britain, Germany, Japan and Australia have all received recent warnings from Hansen about their countries' behavior. In each case, these nations' continued support for the burning of coal to generate electricity has horrified the climatologist. In Britain, he has condemned the government's plans to build a new coal plant at Kingsnorth, in Kent, for example, and even appeared in court as a defence witness for protesters who occupied the proposed new plant's site in 2007.
"On a per capita basis, Britain is responsible for more of the carbon dioxide now in the atmosphere than any other nation on Earth because it has been burning it from the dawn of the Industrial Revolution. America comes second and Germany third. The crucial point is that Britain could make a real difference if it said no to Kingsnorth. That decision would set an example to the rest of the world." These points were made clear in Hansen's letter to the prime minister, Gordon Brown, though he is still awaiting a reply.
As to the specific warnings he makes about climate change, these concentrate heavily on global warming's impact on the ice caps in Greenland and Antarctica. These are now melting at an alarming rate and threaten to increase sea levels by one or two meters over the century, enough to inundate cities and fertile land around the globe.
The issue was simple, said Hansen: would each annual increase of carbon dioxide to the atmosphere produce a simple proportional increase in temperature or would its heating start to accelerate?
He firmly believes the latter. As the Arctic's sea-ice cover decreases, less and less sunlight will be reflected back into space. And as tundras heat up, more and more of their carbon dioxide and methane content will be released into the atmosphere. Thus each added tonne of carbon will trigger greater rises in temperature as the years progress. The result will be massive ice cap melting and sea-level rises of several meters: enough to devastate most of the world's major cities.
"I recently lunched with Martin Rees, president of the Royal Society, and proposed a joint program to investigate this issue as a matter of urgency, in partnership with the US National Academy of Sciences, but nothing has come of the idea, it would seem," he said.
Hansen is used to such treatment, of course, just as the world of science has got used to the fact that he is as persistent as he is respected in his work and will continue to press his cause: a coal-power moratorium and an investigation of ice-cap melting.
The world was now in "imminent peril", he insisted, and nothing would quench his resolve in spreading the message. It is the debt he owes his grandchildren, after all.