A posting at TerraBlog on a recently-publicized controversy at NASA got me thinking about the way the word "theory" has morphed from a neutral scientific term into a dismissive criticism. How often do you hear references to climate change that end with something along the lines of, "But of course it's just a theory"? Well, it is exactly that, which makes it neither more nor less true. Now, words change their meanings all the time; this is part of the beauty of a dynamic language like English. But some changes are unhelpful and should be resisted, because rather than increasing our understanding and clarity of expression, they hinder it. I'd argue that "theory" is a prime example.
According to the definition I learned in endless science classes on the way to an engineering degree, a theory is a hypothesis that fits the observed evidence and can be tested by experiment. The Wikipedia entry on the subject is a bit longer but boils down to pretty much that. So it is factually correct to refer to climate change, the Big Bang, evolution, gravitation, quantum mechanics, and a host of other things as theories. However, that description shouldn't be construed as calling these concepts into question, without reference to some specific evidence that contradicts them.
I'm old enough to remember when there were two competing cosmological theories--in addition to Creation. It turned out that the Big Bang fit the evidence much better, nor has it been disproven by anything we've seen. The competing "Steady State" theory is now all but forgotten. Even when they are superseded by more advanced theories, though, some theories remain valid as limited cases. It took Einstein to plug the gaps in Newton's Theory of Gravitation, but the latter still adequately describes the behavior of essentially every physical object in our world, from dropping a ball to programming a missile. At the same time, we should recall that the history of science is littered with utterly failed theories, such as the ether theory of electromagnetic propagation and the phlogiston theory of burning.
No one today can state with certainty into which category the theory of climate change will eventually fall: unchallenged, valid but limited, or ultimately false. All we can say--and this is what I think the current "scientific consensus" means--is that it fits the observed behavior of the climate over the period in question better than any alternative yet proposed. It also means we haven't found anything that conclusively disproves it. And until refined or disproved, we have no better way of predicting the future behavior of the climate.
I'd love to see an education campaign on the proper meaning of this useful word, to reclaim it from those who misuse it out of ignorance or ideology. This is not a slap at people of faith, of which I am one. If someone doesn't believe in climate change, evolution, the Big Bang, or quantum mechanics, he is entirely within his rights. But at the same time, simply referring to any of them as theories should not undermine it in the eyes of an educated person.