Few things have more bedevilled the debate about global warming than the question of scientific consensus. About what the scientific consensus on the subject is and about what degree of deference should be paid to scientific consensus as such. Both debates have been seriously aggravated by two other factors. Global warming seems to have colossal economic implications, which has activated the concerns of many interested parties; and the ecological nature of global warming has stirred up heated ideological passions that go well beyond the science. It’s all very well to feel either passionate or sceptical about these matters, but how are we to think clearly about them?
David Weintraub’s How Old is the Universe? offers five useful clues. The author has nothing to say about climate science and all parties to the climate debate can, therefore, chill out and think dispassionately here. His concern is about how we can know the age of the universe. He asks:
How have 400 years of science brought us to this point at which astronomers, cosmologists and physicists can claim that the universe came into existence at a specific moment 13.7 billion years ago? And how much confidence should you have in this statement?
These are similar in kind to the big questions that need to be asked (and answered) regarding the anthropogenic global warming hypothesis. But just one of Weintraub’s chapters provides the five useful clues to which I referred.
That chapter is about the discovery that the Milky Way is not the whole universe, but actually a very tiny part of it. The early breakthroughs in modern cosmology had been the shift from a geocentric to a heliocentric view of the solar system and then to a realization, as telescopes became more sophisticated and the understanding of the light spectrum more refined, that there were vastly more stars than anyone had imagined and that they were much further away than ever previously guessed.
Among them there were strange phenomena called spiral nebulae, wispy cloud-like formations that called for explanation. In 1755, the great philosopher Immanuel Kant, in his Universal Natural History and Theory of the Heavens, speculated that spiral nebulae might be what he called “island universes” outside the Milky Way. A debate about this went on for many decades, but there was no scientific consensus one way or the other.
However, in the first decades of the twentieth century, a strong scientific consensus developed that the Milky Way was, in fact, the entire universe. A range of detailed studies in the 1910s, by leading astronomers Vesto Slipher, Harlow Shapley and Adrian van Maanen, seemed to confirm this. Shapley’s work was especially brilliant. He upended the consensus that had reigned since Copernicus that the Sun was the centre of the universe; showing that we should see it as being 40,000 light years away in the heart of the Milky Way. The debate now appeared to be over: Kant had been wrong. But it turns out he wasn’t. In Weintraub’s words:
The steady accumulation of evidence from a decade of work by Slipher, Shapley and van Maanen appeared to have driven the astronomical community toward broad consensus. Spiral nebulae are part of the Milky Way. They are not island universes. The Milky Way encompasses the entire universe. A few years later, new observations proved this consensus completely wrong.
In 1923-24, the brilliant young astronomer Edwin Hubble, having collected a great deal of data using the newly commissioned 100 inch telescope at Mount Wilson Observatory, wrote to Shapley to say that it looked as though Andromeda and M33 were well outside the Milky Way. “The straws are all pointing in one direction,” he commented, “and it will do no harm to consider the various possibilities involved.” Shapley responded with disarming humility, “I do not know whether I am sorry or glad…perhaps both.” Quite suddenly, it had been shown that the universe was vastly larger than the scientific consensus had allowed.
Weintraub asks, “How had the astronomy community, including Slipher, van Maanen and Shapley, been led so far astray?” Slipher, he points out, had made some good measurements but had misinterpreted them and also made statements that were “rash and not supported by sufficient evidence”. Van Maanen’s measurements had been simply incorrect. “Eager to discover what he believed must be true, he misled himself, finding the answers he thought should be in his data rather than the answers truly revealed by his photographs.” Shapley had actually made “excellent measurements, but he did not make enough of them.” Incredibly, he concludes, despite all these errors in trying to bring closure to the island universe debate, the research of Slipher and Shapley was to actually help provide the basis for the next momentous step in Hubble’s research – the discovery that the universe was not only enormously larger than the Milky Way, but was expanding.
How does all this help in regard to the climate science debate? Here are the five ways:
First, it shows that we are justified in being wary of foreclosing major debates based on scientific consensus, since it can be in error.
Second, it shows that the way to challenge and correct scientific consensus is not through polemic or denial, but through specifying crucial variables and deductions and testing them scrupulously, in the manner of Hubble.
Third, it shows that there is, nonetheless, such a thing as scientific consensus and that when handled in the manner just described it tends to prove self-correcting.
Fourth, it shows that ideally such correction will occur, as it did between Hubble and Shapley, on the basis of lucid examination of “the various possibilities”.
Fifth, it shows that overwhelmingly human beings have always lived oblivious to the truth about the natural world and that only exacting and brilliant science has been able to discover what that truth is.
In the climate science debate, we would all benefit from taking note of these five lessons as we seek to develop a rational consensus on the subject.