I came across an interesting paper by Frances Moore and colleagues that considers [d]eterminants of emissions pathways in the coupled climate–social system. In the context of climate science, models that consider both the climate and society tend to not be coupled. For example, global climate models will use emission, or concentration, pathways as input, but these will be pre-defined and will not be influenced by the resulting climate change. Similarly, economic models might use a simple climate model to estimate damages, or to do some cost-benefit analysis, but the latter essentially determines the optimal pathway, but doesn’t really self-consistently couple the climate-social system.
This new paper seems to be the first, or one of the first, that couples a climate-social system. There are quite a large number of factors, but essentially the model estimates the response to various factors and how that might then infuence emissions, and – consequently – climate change. For example, as alternatives become cheaper, their uptake will increase. Similarly, as social norms change, this might influence people’s behaviour in ways that influence emissions. There could be the implementation of policies and laws that will also have an influence. Additionally, our perception of climate change might also directly influence people’s behaviour and the implemention of new policy/laws.
They then run a large suites of models, sampling the various parameters, to produce a suite of outputs that they then group into categories. The main results are shown in the figure below.
The basic result is that a large fraction of their model runs suggest emissions will peak in about 2030, and then fall sharply, leading to warming of about 2.3oC by 2100. There are also some where emissions fall more sharply and warming is closer to 2oC, and others where emission reductions are delayed and warming is closer to 3oC. Overall, most of their models suggest warming of between 2oC and 3oC, but the overall range is from 1.8oC and 3.6oC.
This, however, doesn’t include the full range of climate sensitivity and other possible climate feedbacks, so it can’t quite rule out warming above 3.6oC. However, this does seem to be another paper suggesting that the most likely trajectories suggest warming of between 2oC and 3oC, but that we can’t yet rule out that warming could be kept below 2oC, or that it might exceed 3oC. In some sense this is positive (we can still limit warming to below 2oC) but also somewhat concerning (we can still follow a trajectory that could lead to > 3oC of warming).
From a modelling perspective, this does seem very interesting. The model may rely on a large number of parameters that may not be easy to precisely define, but it is still good to see that some are trying to develop these coupled models that try to self-consistently determine the evolution of the climate-social system.
Determinants of emissions pathways in the coupled climate–social system, Moore et al. (2022), Nature.