It’s an uncertain world

Earlier this year I commented on an opinion piece in Eos, the house journal of the American Geophysical Union. Communications consultant Susan Joy Hassol argued that climate scientists should avoid using words such as “anthropogenic” and “theory” in their press releases and public outreach material, and in effect expunge doubt and uncertainty from public debate surrounding their work. In my view this is not the way to deal with public misunderstanding of climate change. People will instinctively mistrust those who feed them science-lite.

In a recent issue of New Scientist magazine is an interview with physicist and statistician Lenny Smith of the London School of Economics and University of Oxford, whose research focuses on the improvement of numerical models. Smith accepts that anthropogenic climate change is real, but he has much to say about the models used to predict future climate, and modellers who he believes are overselling their results. The problem, he says, is that some scientists go too far in interpreting model results, and downplay the uncertainties involved.

“The temptation to interpret model noise as forecast information invades our living rooms every night. TV weather-forecast maps look so realistic it is hard not to over-interpret tiny details – to imagine that the band of rain passing over Oxfordshire at noon next Saturday requires postponing a barbecue. Rain may indeed be likely somewhere in the area sometime on Saturday, but the details we see on TV forecasts are noise from the models. I think we are having exactly the same problem with climate projections.”

Smith stresses that the models are not useless, and are correct when it comes to the physics of climate change and global warming. But the models cannot give us reliable forecasts on a regional level, and they tend to be very sensitive to initial conditions that from real-world data may not be known to a high degree of accuracy. As someone who in a previous incarnation as a research physicist created models of the Earth’s upper atmosphere, I share Smith’s caution.

You can tweak the initial conditions imposed on atmospheric models, and the computer will churn out sometimes widely differing results. Running the models again and again with different boundary conditions (a method known as ensemble forecasting) can reinforce a particular interpretation, but the results will always contain some uncertainty. And that is fundamental to science, not just the virtual world of mathematical and numerical models.

Climate models have their limits, but we now understand a great deal about the Earth’s climate. Smith believes that the reports produced by the Intergovernmental Panel on Climate Change are credible, but we must read the qualifiers very carefully:

“In the most recent report, for instance, there is an explicit acknowledgement that the range of simulations in today’s models is too narrow. That is, future warming could be greater or less than what is suggested by the diversity between models in the report. It’s good that the qualifier is in there, but it is a hell of a qualifier to find on page 797.”

Failure to discuss the limits of our climate models is potentially dangerous, in that it could hinder society’s ability to respond to climate change, and cost the world valuable time. It also damages the credibility of science and scientists.