I had an interesting exchange with Doug McNeall on Twitter yesterday. Doug is a statistician at the Met Office and an occasional commenter here at BH. We were discussing how scientists convey uncertainty and in particular I asked about a statement made by Julia Slingo in a briefing (warning 10Mb!) to central government in the wake of Climategate:
Globally, 17 of the warmest years on record have occurred in the last 20 years.
This statement was made without any caveats or qualifications.
If I recall correctly, I've posted on the briefing paper before, so for today I just want to concentrate on this one statement. I think Slingo's words represent very poor communication of science since they do not convey any uncertainties and imply to the reader that the statement actually means something. There is, of course, a possibility that it signifies nothing at all.
By this I mean that the occurrence of the 17 warmest years on record could have happened by chance. Doug and I agree that this is a possibility, although we differ on just how much of a possibility. Doug assesses the chances as being very slim based on comparison of the temperature record to climate models. I don't see a problem in this per se, but I think that by introducing models into the assessment, certain things have to be conveyed to the reader: the models' poor performance in out-of-sample verification, our lack of knowledge of clouds, aerosols and galactic cosmic rays, and the possibility of unknown unknowns being obvious ones. Doug reckons our knowledge of clouds and aerosols is adequate to determine that that the temperature history of recent decades is out of the ordinary. This is not obvious to me, however.
But more than that, is the very fact that we are having to introduce models into the equation needs to be conveyed to the reader. Were our knowledge of temperature history better, we would be able to show based on purely empirical measurements that the temperature was doing something different in recent decades. That we cannot do so needs to be conveyed to the reader, I would say.
My challenge to you, dear readers, is to convey in, say, four sentences, the state of the science in this area. (We will take it as given that it is reasonable for Slingo to convey the basic statement about recent temperatures that she has chosen to do. If you feel otherwise, feel free to make your case in the comments.)