Nice LRs! Communicating climate change "causation" 
Friday, March 3, 2017 at 7:21AM
Dan Kahan

The use of likelihood ratios here --" climate change made maximum temperatures like those seen in January and February at least 10 times more likely than a century ago"-- makes this pretty good #scicomm, in my view.

Climate-science communicators typically get tied in knots when they address the issue of whether a particular event was “caused” by global warming.  The most conspicuous, & conspicuously unenlightening, instance of this occcurred in the aftermath of Hurricaine Sandy.

Likelihood ratios (LRs) are a productive alternative to the entanglement of linguistics—because the former invite and enable critical judgment while the latter attempt to evade it.

Obviously, LRs are only as good as the models that generated them.

But if those models reflect the best available evidence, then a practical person or group can make informed decisions based on how LRs quantify the risk involved (Lempert et al. 2013).  That’s what is effaced by linguistic tests that purport to treat causation as binary rather than probabilistic (Anders & Rasmussen 2012; Dolaghan 2004).

LRs also spare communicators from coming off as confabulators when an independent-minded person asks “what does it mean to say indirect/proximately/systematically caused?”

The statement “this event was 10x more consistent with the hypothesis that mean global temperatures have increased by this amount rather than having remained constant” in relation to a specified period conveys exactly what the communicator means and in terms that ordinarily intelligent people can understand (Hansen et al. 2012). 

Or in any case, that is my hypothesis.  While science communicators are doing the best they can to enlighten people in real time, science-of-science –communication researchers can help by empirically assessing the methods they are using.


Dollaghan, C.A., 2004. Evidence-based practice in communication disorders: what do we know, and when do we know it? Journal of Communication Disorders, 37(5), 391-400.

Hansen, J., M. Sato & R. Ruedy, 2012. Perception of climate change. Proceedings of the National Academy of Sciences, 109(37), E2415-E23.

Lempert, R.J., D.G. Groves & J.R. Fischbach, 2013. Is it Ethical to Use a Single Probability Density Function?, Santa Monica, CA: RAND Corporation.

Nordgaard, A. & B. Rasmusson, 2012. The likelihood ratio as value of evidence—more than a question of numbers. Law, Probability and Risk, 11(4), 303-15.


Article originally appeared on cultural cognition project (
See website for complete article licensing information.