During the Energy and Climate Change Committee hearing last week, Peter Lilley asked the men from the Climate Change Committee what evidence would cause them to change their minds about global warming, a question that was fairly studiously avoided. Interestingly, Simon Buckle of the Grantham Institute has written to the FT (not online) to suggest what the reply should have been:
As a physicist, I would modify my view that we are conducting a dangerous experiment with the Earth’s climate if one or both of the following hypotheses were strongly supported by evidence.
First, the identification of a major new process in the climate system that significantly and robustly, over time, moderated the effects of greenhouse gas emissions. At one point, cloud responses to climate change were thought to be a contender for such a “negative feedback” mechanism. Sadly, observations do not support this.
Second, if the timescale of change was much longer than we currently think. We could then perhaps take a century or two to make a transition to a low-carbon economy, instead of perhaps half a century. However, the unprecedented pace of change does not suggest we live in such a world.
While Buckle presents two different scenarios, it seems to me that in fact the two are identical. The only thing that could make the timescale of change much longer is a moderating mechanism of some kind, one that hadn't previously been included in the models. But Buckle is completely wrong to suggest that this mechanism needs to be identified. The models, and the hypothesis of rapid warming, can be falsified quite happily without knowing what factor is responsible. This is the scientific method after all.
Once that uncomfortable fact is taken on board it becomes clear that Buckle should already be questioning his position on global warming. But, not unexpectedly, he concludes that "Extremely well-established physics principles suggest that surface warming will resume and then proceed at a rapid rate". In other words "But the greenhouse effect".
Put in those terms, it becomes clear just how thin his argument is.