One of the fathers of climate science is calling for a wave of lawsuits against governments and fossil fuel companies that are delaying action on what he describes as the growing, mortal threat of global warming.

Former Nasa scientist James Hansen says the litigate-to-mitigate campaign is needed alongside political mobilisation because judges are less likely than politicians to be in the pocket of oil, coal and gas companies.



“The judiciary is the branch of government in the US and other countries that is relatively free of bribery. And bribery is exactly what is going on,” he told the Guardian on the sidelines of the UN climate talks in Bonn.



Without Hansen and his fellow Nasa researchers who raised the alarm about the effect of carbon emissions on global temperatures in the 1980s, it is possible that none of the thousands of delegates from almost 200 countries would be here.



But after three decades, he has been largely pushed to the fringes. Organisers have declined his request to speak directly to the delegates about what he sees as a threat that is still massively underestimated.



Instead he spreads his message through press conferences and interviews, where he cuts a distinctive figure as an old testament-style prophet in an Indiana Jones hat.

He does not mince his words. The international process of the Paris accord, he says, is “eyewash” because it fails to put a higher price on carbon. National legislation, he feels, is almost certainly doomed to fail because governments are too beholden to powerful lobbyists. Even supposedly pioneering states like California, which have a carbon cap-and-trade system, are making things worse, he said, because “half-arsed, half-baked plans only delay a solution.”



For Hansen, the key is to make the 100 big “carbon majors” – corporations like ExxonMobil, BP and Shell that are, by one account, responsible for more than 70% of emissions – pay for the transition to cleaner energy and greater forests. Until governments make them do so by introducing carbon fees or taxes, he says, the best way to hold them to account and generate funds is to sue them for the damage they are doing to the climate, those affected and future generations.



Hansen is putting his words into action. He is involved in a 2015 lawsuit against the US federal government, brought by his granddaughter and 20 others under the age of 21. They argue the government’s failure to curb CO2 emissions has violated the youngest generation’s constitutional rights to life, liberty, and property.



A district court is due to hear the case in February in Oregon, though the federal government has tried to delay the case.

Hansen believes Donald Trump’s actions to reverse environmental protections and withdraw from the Paris accord may be a blessing in disguise because the government will now find it harder to persuade judges that it is acting in the public interest.

“Trump’s policy may backfire on him,” he said. “In the greater scheme of things, it might just make it easier to win our lawsuit.”



He feels a growing sense of urgency. Current government commitments are so inadequate that temperature rises are currently on course to exceed 3C by the end of the century. Hansen says that would mean existing problems – rising sea levels, displacement by flooding, droughts disrupting food production, wildfires consuming forests, worsening storms and hurricanes – would get three times worse.



“Three degrees would be disastrous. You can imagine the planet becoming ungovernable because we would lose the coastal cities where most people live … You’ll see migrants from those parts of the world and also so much disruption to the centres of wealth. So we can’t go down that path.”



Hansen is a believer in direct action. “I’ve been arrested five times. The idea was to draw attention to injustice,” he says. He has also testified on behalf of others who have lost their liberty during climate campaigns. On January, he will speak in defence of an activist who turned off the tar sands pipeline in North Dakota.



But he says litigation and political mobilisation are more effective than protests.



“Those are defence. We should be on the offensive. The lawsuits versus Trump and the fossil fuel industry are offence. People should use the democratic process,” he says. “That’s our best chance. It’s better than getting arrested.”



He draws comparisons with two other great, slow-moving, but ultimately successful legal and public opinion battles: against segregation, where the innate conservatism of judges was overcome by the civil rights movement, and tobacco, where the courts accepted the science despite a misinformation campaign by the industry.



“Climate change is a human rights issue,” Hansen says. “We are seeing injustice against the young. The present generation has a responsibility to future generations.”

Worldwide, the number of legislative activities related to climate change has increased from 99 to 164 in the past two years, according to a report earlier this year by the Grantham Research Institute and the Columbia Law School. Their study found that two-thirds of the litigation resulted in stronger regulations.



The vast majority of cases have been heard in the US, most notably the 2007 supreme court ruling that greenhouse gases are a public health threat. To support future actions, some legal experts are volunteering their services, such as the Earth Justice group in San Francisco, whose motto is: “The Earth needs a lawyer”.



There have been sporadic successes elsewhere, including a lawsuit by a group of Dutch citizens who overturned their government’s move to weaken its greenhouse gas reduction target.



“Over the past 10 years courts are becoming more flexible,” said Cosmin Corendea, legal expert the at United Nations University Institute for Environment. “These isolated cases have started to flash up. It shows the willingness of courts to serve people.”



Corendea echoed Hansen’s call for more climate litigation in the countries that have highest emissions. “Go out there if you have the resources to do that and see if you can help other countries that can’t get to the courts so easily,” he said. “Any good litigation may help. It can raise awareness and create legal practice.”



According to Hansen, the action cannot come too soon. In a press conference at the climate conference, which is the first under the presidency of a small island state – Fiji – he noted that the risks are rising and so should the push for justice.



“We are entering a period of consequences and are in danger of being too late,” he warned. “I have come to note that greenhouse gas climate forcings are accelerating, not decelerating, and sea-level rise and ocean acidification are accelerating. We confront a mortal threat, now endangering the very existence of island and low-lying nations in the Pacific and around the planet. Accordingly, ambition must be increased and enforced.”