There’s been an interesting debate about IAMs. IAMs are Integrated Assessment Models that are used to develop mitigation pathways. In this article, Kevin Anderson argues that IAMs are simply the wrong tools for the job, while Jessica Jewel clarifies the role of IAMs and suggests that IAMs play a central part in the climate debate. Given that things have been somewhat quiet here, I thought it would be interesting to see if we could get a discussion going about this issue.
I wanted to just highlight two comments that caught my eye. Kevin Anderson says
The algorithms embedded in these models assume marginal changes near economic equilibrium, and are heavily reliant on small variations in demand that result from marginal changes in prices.
As I understand it, models of socio-economic systems are largely empirical; the system is too complicated to describe via fundamental equations, and so the models are based on what has happened in the past. I think it’s possible to run these models under scenarios that differ greatly from what we’ve experienced before, but I suspect they’re mostly valid when considering how we, and our economies, would respond to small perturbations. Given that what would be required to achieve some of our goals, it’s not really clear that such models really are all that useful.
Jessica Jewel, however, argues that IAMs to answer what if questions about the future consequences of decisions or developments. I think this is a perfectly valid argument. All models are essentially wrong, but can still be very useful for understanding how a system might evolve.
However, Jessica Jewel also says
The challenge of evaluating feasibility is that the pathways are constrained not only by economic costs and technical complexity, but also by socio-political acceptability.
This is something I’ve always struggled with. Of course, we do need to be aware of socio-political reality, but physical reality doesn’t really care about what we regard as socio-politically acceptable. To achieve some of our climate targets would require doing things that are essentially unprecedented (for example, changing our entire energy infrastructure in a matter of decades). How do we do so if we limit ourselves to doing things that we’re comfortable doing? Of course, I’m not suggesting that we consider doing things that would be regarded as morally unacceptable, but it seems likely that we may have to consider pathways that will change our lifestyles in ways that we may not be entirely happy about.
Of course, maybe socio-politically acceptable includes pathways that we would regard as socio-politically uncomfortable, but this never seems clear to me. It’s also quite possible that I simply don’t really understand IAMs and that they are a perfectly suitable tool for helping us determine mitigation pathways. However, there just seems to be a disconnect between economists suggesting optimal pathways that would lead to around 3.5oC of warming, and scientists who are suggesting that it’s imperative that we limit warming to 1.5oC.
As usual, I’ve written too much; the idea was to try and provoke a discussion. I’ve also tried to be slightly provocative, so feel free to challenge this. It would certainly be interesting to hear from some who thinks IAMs really are useful tools for developing mitigation pathways.
I should probably have made clearer that there are essentially two types of IAMs (which I have found rather confusing, and may still not fully understand). The ones being discussed in the debate between Kevin Anderson and Jessica Jewel are – I think – ones that try to actually model the evolution of the energy system and other GHG-emitting systems and are (I think) coupled to a simple climate model. The other type has simplified relationships between the various factors (economic growth, costs of mitigation, damages due to climate change, etc) and are used for cost-benefit analyses. The one that suggested an optimal pathway that would lead to warming of 3.5oC was one of the latter, and was the DICE model developed by William Nordhaus. Thanks to Steve Forden for pointing this out.
Debating the bedrock of climate-change mitigation scenarios – Nature article with the debate between Kevin Anderson and Jessica Jewel.
The human imperative of stabilizing global climate change at 1.5°C – article by some of the authors of the IPCC SR1.5 report.
How Two Wrongs Make a Half-Right – 2013 post by Michael Tobis highlighting some potential issues with IAMs.
A Review of Criticisms of Integrated Assessment Models and Proposed Approaches to Address These, through the Lens of BECCS – a paper reviewing the criticisms of IAMs.