Hansen is an elder of the climate change debate. An atmospheric physicist who spent the bulk of his career at NASA, his 1988 testimony to Congress was a milestone in raising public awareness of global warming, not least his call to “stop waffling”. He’s happy to take his science to politics; as well as formal advice, he’s been arrested over the Keystone pipeline extension, gave pivotal evidence at the Kingsnorth trial and has called for the CEOs of fossil fuel companies to be tried for crimes against humanity. He is also a strong advocate for nuclear power.

Perhaps most interesting is Hansen’s use of his identity as a pensioner in his climate activism. He often uses his grandchildren in making the case for action on climate change, but there is also the freedom of sorts which can come to professionals in old age. When he left NASA in spring 2013, he told the New York Timesthat as a government employee, he couldn’t testify against the government but, in retirement, could take a more active role in lawsuits challenging the federal and state governments over their failure to limit emissions. He also added “At my age, I am not worried about having an arrest record.” It’s going to be interesting to see what Hansen does with his retirement, and if others follow.