I thought I would post this video of a talk given by Tim Palmer. The basic message is that climate change is neither a hoax, going to be catastrophic, or going to be benign (Lukewarm). What climate science can (and does) provide is a quantifiable risk of various outcomes, from relatively benign to catastrophic. In my view, a key point is that this depends both on how sensitive our climate is to external perturbations, and on our future emission pathways.
What I found particularly interesting in the video (which is where it’s set to start) is a demonstration of that even though the system is chaotic, we can still estimate the response to an external forcing. If a system is chaotic, then it is very sensitive to initial conditions. This makes it difficult to precisely determine a future state. If, however, we know the range of possible states, then we can also determine how some external influence might bias the system so that it preferentially ends up in certain states, rather than others. Therefore, even though our climate is chaotic does not mean that we can’t estimate how it will respond to external perturbations (in this case, typically referred to as external forcings).
At around 30 minutes there is also a discussion of energy balance models and why we shouldn’t necessarily trust their lower climate sensitivity estimates. The basic argument is that we haven’t yet doubled atmospheric CO2 and so these estimates will likely miss some of the non-linearity in the response. I would argue that this is on top of them not even ruling out – with high confidence – higher climate sensitivity values. Anyway, I’ll stop there. The video is below.