Oren Cass has an article in the Wall Street Journal called Doomsday climate scenarios are a joke. It’s based on a report that he has written for the Manhattan Institute. The Manhattan Institute publishes a magazine called the City Journal which did once have an article by Rupert Darwall, in which he defended Murry Salby, so that doesn’t bode well. However, I don’t think that Oren Cass’s article/report are completely without merit.
His article is actually about economic models, rather than physical climate models. His suggestion is that in some cases the assumptions don’t make sense (they ignore, for example, that we can adapt to some of the changes) while in others what the models imply don’t make sense (some very poor countries today will become – because of warming – much richer than countries that are very rich today). If what he say is correct, then it does seem odd. On the other hand, I’m aware that sometimes modellers make assumptions for reasons that may not be immediately obvious. For example, maybe ignoring adaptation presents a worse case scenario, but also provides some indication of what we would need to do to address this (which is not cost-free). On the other hand, my limited encounters with economists might suggest that sanity checking their model results is not one of their strengths.
In many respects, though, I think Oren Cass’s article/report misses the point. Our options are not simply to adapt, or mitigate. We will have to adapt to some of the changes, but should also be thinking about what to do to avoid some of the potential changes (which will largely require emitting less CO2 into the atmosphere than we otherwise could). Precisely how to do this is not necessarily obvious, but there are presumably two extremes that bound the options. Burning everything will almost certainly lead to changes that will prove very damaging. Similarly, immediately halting all emissions will also be pretty catastrophic. So, it presumably has to be somewhere in between these two extremes and there are indeed analyses that provide policy instruments (a carbon tax, for example) that could lead to some kind of optimal pathway.
There are also, in my view, other things to consider. The changes are probably – without technological intervention – irreversible on human timescales. If they turn out to be more difficult to deal with than Oren Cass appears to suggest, we don’t get to easily go back. Also, stabilising global temperatures will essentially require getting emissions to about zero. However, given that we can’t do this immediately, there will always – in reality – be some amount of committed warming. It would therefore seem sensible to think about reducing emissions before it becomes patently obvious to everyone that we should do so. As someone said on Twitter (Peter Jacobs, maybe) the best time to start emission reductions was 20 years ago. The second best time is now.
I’ll finish with my perspective, mostly due to being a physicist. Our climate is a complex, non-linear system. It has, however, been remarkably stable for quite some time, and we’ve almost certainly benefitted from this quasi-stability. However, we’re now pushing it out of balance. For small perturbations, we’re reasonably confident that the response will be linear and that we understand quite well what will probably happen. We do, however, have the potential to produce a large perturbation and, if we do so, the response becomes much more uncertain. This should really make us more concerned, not less.