Professor James Hansen's last formal engagement was delivering a keynote paper to the American Geophysical Union Autumn meeting. After that, he spent the holidays not enjoying wintry walks or taking advantage of the sales, but doing something altogether more industrious. "I'm writing a paper to provide the scientific basis for [law] suits against the government - just to make them do their job," he says.
Hansen, director of the Nasa Goddard Institute for Space Studies and one of the world's leading climate scientists, has not always been as politically engaged as he is now. He had hoped that politicians would respond to the scientific community by taking action to minimise the risks from climate change. But over the course of 30 years advising US administrations from Jimmy Carter to George W Bush, he has seen how the influence of the energy companies has corrupted the political process. Now with just a small window of opportunity left in which to stabilise our climate before it slips out of our control, he has been busying himself with writing to key heads of state around the globe, advocating civil resistance against the coal industry and getting himself arrested while campaigning against mountain-top removal coal mining.
After his famous testimony before a Congressional committee in 1988 that human-induced global warming had begun, Hansen spent the next 15 years turning down most requests for talks and interviews, preferring to focus on research. He overcame his reticence in 2004, when he became angered by the Bush administration's political interference in climate science. He was seized by the need to ensure the public had the facts about the risks posed by climate change, but he also became outspoken on policy issues, crossing a line that many scientists steer clear of.
"I realised that if we [scientists] don't help to connect the dots from what the science says to what the implications are for policy, then those dots get connected by people who have special interests," says Hansen, explaining his decision. "I think scientists are able to be objective. Governments just don't face the facts clearly. And it's scary because as scientists we can see what the implications are for our own children and grandchildren."
At a time when many scientists are on the back foot after the pre-Copenhagen attack on the climate science initiated by the release of internal emails by researchers based at University of East Anglia, it's a brave position to take. It's also one that was recognised in 2006 when the American Association for the Advancement of Science honoured him with its Scientific Freedom and Responsibility Award for "his courageous and steadfast advocacy in support of scientists' responsibilities to communicate their scientific opinions and findings openly and honestly on matters of public importance".
In 2008 he published a landmark paper along with some ten co-authors, "Target Atmospheric CO2: Where Should Humanity Aim?" which redefined our understanding of what constitutes dangerous climate change. Its conclusion that we need to reduce the levels of carbon dioxide in the atmosphere from 390 parts per million (ppm) to below 350, set the stage for a global campaign to put the number 350 at the heart of international climate policy. By the time of the UN climate talks in Copenhagen in December 2009, a majority of more than 100 countries had signed up to the target. But the weak agreement that emerged from the UN talks in Cancun does not endorse the 350 figure and instead refers to the outdated threshold for average global temperature rise of 2C.
"Two degrees Celsius is guaranteed disaster," says Hansen scornfully. "It is equivalent to the early Pliocene epoch [between 5.5 and 2.5 million years ago] when the sea level was 25m higher. What we don't know is how long it takes ice sheets to disintegrate, but we know we'd be starting a process which then is going to be out of control. Because the way it works - the planet is out of energy balance, most of the additional energy is going into the ocean, which melts the ice shelves, which then allows the ice sheets to discharge ice more rapidly - if you want to stop that and you've pushed it up to two degrees, then you've got to cool off the ocean. Well that's going to take hundreds of years. So you would have a situation which can't be fixed except with some geo-engineering, which is a pretty awful inheritance to leave for our children."
For Hansen, the recent UN talks were doomed to failure since they did not address what he calls "the fundamentals". The starting point should be recognising the physical boundary constraints of the Earth's climate system and working out how to live within them.
"We've reached a point where it's clear we can't burn all the coal or unconventional fossil fuels [such as oil from tar sands, deepwater drilling and sources revealed by melting ice]. We've got to phase them out. The large pools of oil and gas that are readily available to Russia, Saudi Arabia and the Middle Eastern countries is enough to get us well over 450ppm."
At the UN talks, the rich countries still had high expectations that markets in carbon dioxide would play a central role in the final deal agreed in Durban, South Africa at the end of 2011. Carbon markets, or what's often called "cap and trade", provide access to "offsets" for rich countries which allow them to buy in carbon reductions from developing countries instead of reducing emissions within their national borders. However a 2008 Stanford University study found these supposed carbon cuts to be largely illusory.
For some time Hansen has been on record slamming this approach. He says that in talks with officials in the UK, the US, Norway, Sweden, Australia, Japan and Netherlands, government representatives all say they will bring down emissions by using carbon markets. "You can prove that this is horseshit because they're building more coal plants. The fossil-fuel industry wants to continue with something close to business as usual and that is what they get with cap and trade and with offsets. But governments are supposed to be operating for the benefit of citizens not for the benefit of powerful industries that have money."
Hansen's solution is a framework built around the introduction of a carbon tax in both the US and China, and he has recently turned his attention to focusing on the benefits to China from adopting this approach.
"It's as certain that as long as fossil fuels are the cheapest energy, we will just keep burning them. So we have to put a tax on carbon which rises over time. China has said flat out that they will not accept a cap. However, China has every reason to tax carbon because they have invested a lot in carbon-free energy. They're now number one in production of solar, wind and nuclear. But clean energy is not going to take over from dirty energy if fossil fuels remain the cheapest. So they need to put a price on carbon within their country and they're now actually thinking about that. They can see that economically they will be better off if the world starts to move towards clean energy, as they will be in a great position to sell these technologies to the rest of us.
They want to solve their air pollution and water pollution problems; they don't want to have the fossil-fuel addiction that has the United States sending soldiers all around the world; they don't want to suffer the climate damages because they are much more vulnerable than most countries."
Hansen's idea is that 100 per cent of the revenue collected from a carbon tax is returned in equal amounts to citizens, which means that those with lower carbon footprints are likely to be better off. In his latest book, Storms of My Grandchildren, Hansen says that Congress liked cap and trade because "it thinks the public will not figure out that it is a tax" and a tax in which energy companies and financial speculators reap the dividends.
Daphne Wysham, a fellow at the Institute for Policy Studies think tank, is part of a growing coalition that supports the idea of a carbon tax. With cap and trade legislation a dead duck in the new Republican-dominated House of Representatives, Wysham figures that campaigners in the US have two years to start educating the public about the benefits of "tax and rebate" before the political complexion of Congress shifts again. In the meantime she's bullish about the potential for US action. "We may exceed the targets that the US has put on the table through a switch to natural gas from coal and a ramping up of wind energy; in addition, there's a major pushback from the grassroots against existing and proposed coal-fired electricity plants based on their mercury and other emissions." But however the political climate changes, and despite the shifting sands of globalisation, Hansen will be using his expertise to try and avert a toxic timebomb for our descendants and their planet.