| I once took a course on Scientific theory, using a book by Karl Popper as a text. I confess that I only got a B; it was genuinely a struggle for me. But one thing that I understood deeply was his theory of falsification. |
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It is ironic that climate change deniers have a tendency to demand "proof" that humans are behind climate change (or proof that there is any climate change whatsoever).
Proof is an interesting notion, especially to a mathematician. To a scientist, however, it is anathema. It simply does not exist. Carl Sagan said it well, but gently, in his testimony before Congress: "To require that scientists provide an absolutely ironclad, guaranteed value of how much the temperature will go up is probably asking too much. The calculations involve many factors, and you cannot be absolutely sure that you have included every one of them. What is striking is the unanimity of all of the calculations, so if a few degree increment in the global temperature is a bad thing then you ought to start worrying about what to do in that case. Also, you ought to start worrying about whether there is some way to avoid putting more carbon dioxide into the atmosphere." (See my piece on the "Big Picture").
If I may be so bold, I'd paraphrase Sagan as saying that the preponderence of evidence is on the side of those who hold that the temperature will rise a few degrees under current carbon emission scenarios. And he stated this 30 years ago, but it is still true -- indeed, even more so.
The crucial point, however, is that science does not deal in truths: it deals in theories, each subjected to testing. A theory is only interesting so long as it is falsifiable: can be tested and found lacking. There are no facts in science, only theories. That gravity is an inverse square law is really only a theory: it's been tested, and we're pretty sure that the exponent's no more than 2.000000001, say, and no less than 1.999999999; but the point is that I'm pretty sure that we can't (yet) say for a fact that it's not an inverse 1.99999999999999999999999999999 rule (and add a few more 9s if that's not working...). Scientists will keep chasing down those decimals, until they've run out of 9s, or until they can bound the true value away from 2 (at which point they'll declare the inverse square law false -- it will have been falsified.
But (just to be clear) you won't find a lot of folks running around denying that gravity's an inverse square law. But then you don't find scientists saying that it's been proven, either.
So it is with climate change: In August of 2013 Reuters obtained a leaked copy of the Intergovernmental Panel on Climate Change (IPCC)'s upcoming report on the status of climate change, and reported that "...the study by the U.N. panel of experts, due to be published next month, say[s] it is at least 95 percent likely that human activities - chiefly the burning of fossil fuels - are the main cause of warming since the 1950s." Scientists don't declare anthropogenic climate change certain, but they're claiming that it's more certain than ever. They've tested the theory, in attempts to falsify it, and -- so far -- they've failed.
Some deniers seize on the scientists' inability to assert with certainty that something is true (e.g. "it is 100 percent likely that human activities ... are the main cause of warming since the 1950s"), and so they believe that their theory that human activities are not the cause of warming -- if there is indeed warming -- is equally valid. In that they are incorrect, as the preponderence of evidence is on the side of the IPCC.
It is not true that all theories are equal. Therein lies the biggest mistake that the denialists hope to promulgate.
Now it is true that mathematicians are able to prove things; but they are only able to do so within a context. In other words, truth is contextual, and not absolute. Mathematicians have axioms, which they hold to be "self-evident" ("We hold these truths to be self-evident...." is the establishment of an axiomatic government). Then, proceeding from those axioms via logical rules, mathematicians arrive at "truths". But change the axioms, and the truths may go out the window.
So even in this purest of sciences (the "Queen" of the sciences), truth is only relative.
Do not, therefore, expect the IPCC to ever declare with certainty that climate change is ultimately due to humans -- it may be that giant space hamsters are responsible, as high school teacher and climate change video maker extraordinaire Greg Craven may try to convince you. Enjoy his stuff!