It was Henry James who said that detective stories should be considered "not so much works of art as works of science". His remark has gained new pertinence with the appointment of a Sherlock Holmes fan, Professor Chris Rapley CBE, as director of the Science Museum. Holmes' well known methods of deduction and logic, of using first-hand evidence and reasoning from what you see, of keeping a blank mind and approaching facts in a "cold and unemotional manner", may soon be helping visitors to the South Kensington museum sort out for themselves what to think about overpopulation, stem-cell research, genetic modification and climate change.

This hasn't, traditionally, been the role of the Science Museum. Founded in 1857, the museum has developed through a series of bequests and acquisitions into a vast, unwieldy collection of 300,000 objects, only 7% of which are on display. A month into his job, Professor Rapley is sitting in his South Kensington office, telling me that broadly the museum's collection celebrates "the advances in technology since the Industrial Revolution, right up to, but not quite including, today".

He wants to turn that on its head. "Its image is that it looks backwards through its collection. It's a museum, it's historical, and it's for children. Where we want to go with it, the tag line is, ‘the museum of the future'." He would like the museum to be sufficiently up-to-date that someone seeing, say, a climate-change sceptic on TV, might think, "I'm confused about climate change. I'd better go to the Science Museum and see what they're presenting in order to help me make up my mind."

Rapley says that he first learnt the pleasures of working things out using the evidence in front of him from Sherlock Holmes and that this ultimately led him to his new job. He was introduced to the stories by his English teacher at St. Edmund's, Bath, when he was ten or 11, in about 1957. "Once I got into it, I just burned my way through the lot of them." Rapley's father and his grandfather had been engineers. "And engineers tend to take things to bits and often not be able to put them together again. They are always curious about how things work."

It's easy to see why Conan Doyle's stories appealed to the son and grandson of engineers. "You're offered all the pieces of the jigsaw, but it's Sherlock Holmes who puts it all together. What I found thrilling was that ‘wow' moment when it all came clear and, looking back, all the evidence was there." Rapley did a degree in physics and a PhD in X-ray astronomy. "The more I got into physics and chemistry, particularly physics and mathematics, those 'wow' moments emerged, because you suddenly realise you've calculated something."

The idea that "here are the pieces, now work it out for yourself" underlies his approach to the Science Museum. Rapley, like Holmes, thinks most things are elementary. "I do not believe that there is a single piece of science that anyone does that could not be explained to Granny in very simple terms, because the principles are always pretty straightforward actually." The problem at the moment is that scientists are not very practised at "stripping away the arcane stuff and just explaining what it's all about". For Rapley, "it's all to do with telling stories".

For the first half of his career, Rapley had been a space astronomer, working as principal investigator on both NASA and European Space Agency satellite missions. (Don't tell him something isn't rocket science, because he knows exactly what is and what isn't.) But halfway through his career, he changed and became an "earth observer". Astronomy felt a bit "indulgent", earth-observation looked as if it might be more directly useful. "At the time there were a few really insightful luminaries, who were saying, ‘You know, I reckon humans are going to change the way the planet works and that could be a bad thing'." (James Lovelock was a particular influence.) Rapley's work on earth systems led him to take over as head of the British Antarctic Survey. "So many roads lead to the polar regions, if you really want to understand how the planet works."

"There is nothing like first-hand evidence," wrote Conan Doyle in "A Study in Scarlet". It would be hard to view first-hand evidence in a cooler light than the Antarctic. "I am in a position," says Rapley, "to have seen the evidence that climate change is real, climate change is driven by humans, and it's serious enough that we need to do something about it."

The museum won't, however, be turning against it own fossil-fuel exhibits, or even some of its sponsors. "People sometimes expect me to be very anti-oil-company or anti-coal-company," Rapley says. "They couldn't be more wrong. I know I couldn't survive for more than a week without the constant flow of hydrocarbons upon which everything depends: my food supply; my energy supply; my transport supply. So I'm really glad they're out there. It's just a big shock and a pity for all of us that this wonderful energy supply, which has completely transformed the human condition, has a big downside, and we're just beginning to recognise that we had better do something about it."

One of the museum's 300,000 exhibits is a Formula One car. The other day someone suggested to Rapley that Formula One be banned. "It's daft. It's not what you should be doing. If the future of the world that you offer people in a decarbonised society is hairshirt, miserable, and you-can't-do-anything-fun, then nobody's going to buy into it." On the other hand, he doesn't believe in carte blanche for gas-guzzlers: he has described Jeremy Clarkson, the gung-ho Top Gear presenter, as "reckless".

He says he would never be able to point to one single piece of evidence that prooves climate change. "The point of climate change is that no individual result from a particular point on the surface of the planet really counts. It's the aggregate picture that's built up." He stresses that the Earth's systems are so complex that some of the evidence is counter-intuitive. "If you look at all the world's glaciers, 80% of them, nearly 90% of them, are retreating. But 10% of them are advancing. Well, that's overwhelming evidence that they're going in a particular direction."

When it comes to discussing what can be done, Rapley sees great uncertainty. "That's work in progress and the museum will offer as wide a range of information as possible and encourage visitors to draw their own conclusions." But the museum will take "a strong position" on the central issue itself.

"Sherlock Holmes used to have this adage that however unlikely and uncomfortable your conclusion may be, if all other possibilities had been ruled out, you were probably right. Nobody would be happier than me if tomorrow, or later today, it turned out that for some reason we had got it all completely wrong and actually we can carry on using fossil fuels and there's no problem and everything's great. It just isn't going to happen. Because all the evidence is that that is not true. And Sherlock Holmes would have concluded that quite quickly."

Photograph by Peter Searle