Can We Actually Even Tell if Humans Are Affecting the Climate?
We know, with great certainty, that the overall average temperature of the Earth has warmed by several degreees in the last 400 years, since the end of the Little Ice Age. Before that was a period called the Medieval Warm Period; before that was another cold period; and back at the time of the Romans there was a long period that was significantly warmer -- Southern Britain was a wine-growing region. What we're a lot less certain about is "why?"
Of course, the "why?" here has been, shall we say, pretty controversial. It's worth wondering about the controversy and about the social mechanisms through which science is done -- I wrote about them during the Climategate controversy as the "social contract of science" -- but that's not what I want to talk about today. Instead, let's talk about how a scientist thinks about these sorts of questions and arrives at new answers. Back in grad school we called that "doing science," and it was something everyone liked doing and wished they could be doing instead of whatever they actually were doing, like faculty meetings and refereeing papers.
The process of "doing science" is something you usually learn more or less by osmosis, but there are some good hints around. One of the best is a paper from the 16 October 1964 issue of Science, "Strong Inference" by John R Platt. Let's say we have some phenomenon of interest, like global warming, or high blood sugar, or that damned yellow patch in my lawn. We want to know why it happens. Platt's strong inference describes the process we should use when "doing science" as:
- We generate a number of alternate explanations, hypotheses, that might explain the phenomenon.
- For each hypothesis, we come up with an experiment which will prove the hypothesis wrong. That is, not one that "proves the hypothesis," but one which, if successful, would disprove or falsify the hypothesis. (Sir Karl Popper argued in his book The Logic of Scientific Discovery that this falsification was the core of scientific knowledge.)
- We do the experiments. If an experiment falsifies a hypothesis, we discard it ruthlessly. Then we go back to (1) and try again.
A lot of times, the rub -- and the really creative thinking -- comes in from finding the right experiment. Richard Feynmann was known for an ability to see right through a problem to a simple and elegant experiment that would disprove a hypothesis. He demonstrated this during the review following the Challenger disaster. You may remember that the launch happened on a very cold morning in January; less than two minutes after launch the Space Shuttle Challenger blew up, killing all seven astronauts.
The question, as always, was "why?"