Judith Curry testified before the US House of Representatives. You can read her evidence and post. In a follow up post Judith suggests that there is some common ground that we can build on. I’m not really convinced that there is. I’ll try to explain why here.

For starters, Judith’s evidence starts with the claim that

…, there is considerable disagreement about the most consequential issues: whether the recent warming has been dominated by human causes versus natural variability

This is simply not true. A vast majority of relevant experts accept that human factors are the dominant cause of recent warming. As an aside, I would still like to better understand what those who dislike consensus messaging think we should do to address such claims.

The bit I wanted to highlight, though, was the following

[o]verreaction to a possible catastrophic threat may cause more harm than benefits and introduce new systemic risks, which are difficult to foresee for a wicked problem.

Firstly, I don’t agree that this is really a wicked problem. At least, not in the sense that we don’t know what needs to be done (get emissions to zero). It’s probably true that if we overreact, then we could do more harm than good. However, few who argue that we should be reducing emissions are suggesting that we should do so in a way that produces catastrophic economic damages.

Patrick Brown has a nice post that illustrates a key point. It’s already clear that there are economic (and other) benefits to emitting less than we otherwise could. Of course, this doesn’t tell us how much less we should emit, but it does tell us that some kind of optimal pathway involves some level of emission reductions.

However, if you want to see an actual estimate of an optimal pathway, you can consider a recent paper by the winner of the 2018 Nobel Memorial Prize in Economics. As I discussed in this post, I don’t really think that this is some kind of definitive optimal pathway; I think there are too many factors that can’t be properly incorporated into these models, and it doesn’t even rule out warming above 4K. However, apart from this still potentially leading to substantial warming by 2100, this is not all that relevant to what I’m trying to get at here.

Consider the emission pathway associated with Nordhaus’s optimal pathway (Figure on right). Bear in mind that this is an optimal pathway that is expected to lead to about 3.5K of warming by 2100, with an uncertainty of about 0.9K (i.e., it doesn’t rule out warming by more than 4.5K). Yet, even this optimal pathway still has emissions increasing slowly for a couple of decades, peaking around 2040, and then reducing towards zero.

So, even an optimal pathway that potentially leads to quite substantial warming would still require starting to decouple emission increases from economic growth very soon, peaking emissions in ~20 years, followed by substantial emission reductions. It’s hard to see how this could happen without some kind of explicit intervention (a combination of a carbon tax, investment in innovation, and incentivising some changes in behaviour). I don’t think that no regrets policies, that essentially everyone is happy with, is going to be sufficient.

It’s hard to see how there can be common ground if some don’t even seem to accept the basis for the discussion. We can certainly argue about how to reduce emissions, when to start reducing emissions, and how fast to reduce them. It’s hard to do so with those who argue that

[a]ttempting to use carbon dioxide as a control knob to regulate climate on decadal to century timescales is arguably futile.