A raging fire in the house where they both live, together with many other people and animals, sparks a lively debate between two scientists. The first – let us call her Professor Empiricus – says that the fire is a great opportunity for testing various theories, about the flammability of building materials, the relationship between heat and the rate of destruction of buildings, the effects of changes in wind direction on the intensity of conflagrations and so on. The second scientist, Dr Suasor, has somewhat different ideas: “We should be crying out, ‘The house is on fire’, and then either try to put it out or evacuate the building.” “But that is not the role of the scientist,” replies Prof Empiricus with the sweet smile of implacable reason.

My tale may be a bit of a caricature but it does capture something of an ongoing and quite fierce difference of opinion in the climate science community. To what extent should climate scientists speak out, or cry from the rooftops, in the debate on global warming? Certain climate scientists, such as James Hansen, long-time head of Nasa’s Goddard Institute of Space Studies in Manhattan, and Michael Mann, director of the Earth System Science Center at Pennsylvania State University, have for many years rejected the idea that scientists should maintain an impartial position and avoid value-laden language or political posturing.

Hansen retired from Nasa last year and now runs the programme on Climate Science, Awareness and Solutions at Columbia University. He has backed up his belief that science cannot and should not be divorced from what he sees as its responsibility in communicating the gravity of the climate crisis to citizens by engaging in acts of civil disobedience; he has been arrested following protests in front of the White House against the extension of the Keystone XL pipeline.

Michael Mann is another who believes, he wrote in The New York Times in January this year, that “it is no longer acceptable for scientists to remain on the sidelines”. In a sense his hand was forced, after a study he co-wrote in 1998, showing that the average warmth of the northern hemisphere had no precedent for at least 1,000 years, led to him being “hounded by elected officials” and “threatened with violence”. He makes a provocative parallel with the advice from the US Department of Homeland Security to citizens to report anything dangerous that they witness: “If you see something, say something.” Scientists, the overwhelming majority of them, can see a serious, ever-deepening threat: it is their responsibility to speak out.

One of the most intelligent repudiations of the idea that climate scientists are under a moral obligation to take up the role of advocates comes from Tamsin Edwards, an academic at the University of Bristol in the UK. As a climate scientist concerned about the environment, Edwards feels under pressure to be a political advocate. But she resists that pressure, believing “advocacy by climate scientists has damaged trust in the science”. Ultimately, she says, “I care more about restoring trust in science than about calling people to action.”

I respect Edwards for stating the position so clearly (she writes an excellent blog entitled All Models Are Wrong) but here I disagree with her, not on scientific grounds but on ethical ones. Her position taken to its logical extreme leads to the view that it is better that most life on earth should perish than that the purity of the scientific method should be compromised.

Several of the greatest scientists in history did not have qualms about proselytising or calling people to action, when they felt it was necessary. Galileo, canny operator that he was, was still not content to sit on the sidelines. Despite the extreme sensitivity of the subject – the challenge to the old biblical, Aristotelian view of the earth as centre of the universe by Copernican heliocentrism – he still wrote his Dialogue Concerning the Two Chief World Systems to give support to the Copernican view. He did not help himself by making Simplicius, the upholder of the old geocentric view, use words close to those of Pope Urban VII (and by giving him a name that sounds suspiciously like “simpleton”). Galileo was tried by the Inquisition, found “vehemently suspect of heresy” and held under house arrest for the rest of his life.

Albert Einstein was another great scientist who did not let a concern for the purity of the scientific method stop him from using value-laden language, or from taking up sometimes controversial political positions. He wrote to President Roosevelt on August 2 1939 warning that the imminent possibility of building atomic bombs using uranium called for “watchfulness and, if necessary, quick action on the part of the Administration”.

Later Einstein told Newsweek magazine, “had I known the Germans would not succeed in developing an atomic bomb, I never would have lifted a finger”. But I don’t believe that means he was wrong to write the letter.



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