Are climate models falsifiable?

Roger Pielke, Jr. has stirred up a “hornets’ nest” by raising a very straight-forward question at the global-warming advocacy headquarters Real Climate. Roger’s question was:

There are a vast number of behaviors of the climate system that are consistent with climate model predictions, along the lines of your conclusion: “A cold Antarctica and Southern Ocean do not contradict our models of global warming.”

I have asked many times and never received an answer here: What behavior of the climate system would contradict models of global warming? Specifically what behavior of what variables over what time scales? This should be a simple question to answer.


You may find the objections and the absence of useful responses rather surprising. In contrast, I found Roger’s commentary clear and accurate. I hope that his point about the models being “largely of exploratory or heuristic value” results in a full expansion. Excerpts:

…The good news is that there are a range of serious scholars working on the predictive skill of climate models. And there are some folks, myself included, who think that climate models are largely of exploratory or heuristic value, rather than predictive (or consolidative). (And perhaps a post on why this distinction is of crucial importantce may be a good idea here.) But you won’t hear about them at Real Climate.

Once you start playing the “consistent with” or “not inconsistent with” game, you have firmly placed yourself into a Popperian view of models as hypotheses to be falsified. And out of fear that legitimate efforts at falsifiability will be used as ammunition by skeptics (and make no mistake, they will) in the politics of climate change, issues of falsification are simply ignored or avoided. A defensive posture is adopted instead. And as Naomi Oreskes and colleagues have observed, this is a good way to mislead with models.

One of the risks of playing the politics game through science is that you risk turning your science – or at least impressions of it – into pseudo-science. If policy makers and the public begin to believe that climate models are truth machines — i.e., nothing that has been, will be, or could be observed could possibly contradict what they say — then a loss of credibility is sure to follow at some point when experience shows them not to be (and they are not). This doesn’t mean that humans don’t affect the climate or that we shouldn’t be taking aggressive action, only that accurate prediction of the future is really difficult. (For the new reader I am an advocate for strong action on both adaptation and mitigation, despite what you might read in the comments at RC.)

So beware the “consistent with” game being played with climate models by activist scientists, it is every bit as misleading as the worst arguments offered by climate skeptics and a distraction from the challenge of effective policy making on climate change…

Read the whole thing, which includes other important references. I particularly recommend this downloadable Chapter 7:

Pielke, Jr., R.A., 2003: The role of models in prediction for decision, Chapter 7, pp. 113-137 in C. Canham and W. Lauenroth (eds.), Understanding Ecosystems: The Role of Quantitative Models in Observations, Synthesis, and Prediction, Princeton University Press, Princeton, N.J. (PDF)