I’ve been struggling, more than usual, to find things to write about. Everything seems to just be a bit of a mess. The pandemic itself, how it’s been handled in some cases, and the protests in the USA, especially how the protestors are being treated by the police. I just don’t feel that I really have the words to describe what’s currently happening in a way that would do it justice.
However, given that it’s been rather quiet here, I thought I would just highlight one paper that I found interesting, and useful. The lead author is Flavio Lehner, and the paper is called Partitioning climate projection uncertainty with multiple large ensembles and CMIP5/6. The paper seems to be open access, so I don’t need to say too much. Essentially, it ues ensembles of models to estimate the sources of uncertainty and their magnitudes.
One of the key figures is below. It shows 3 different model ensembles, their global surface temperature projections for different scenarios, and – finally – how the fractional contribution to total uncertainty. The key results are that for long-timescales (many decades) internal variability contributes little to the total uncertainty (essentially, it averages out). The largest source of uncertainty is scenarion uncertainty (i.e., how much are we going to emit). A similar result is obtained if you consider changes in global mean precipitation.
Although the model uncertainty (defined as uncertainty in the forced response and structural differences between models) is not negligible, it’s clear that a dominant source of uncertainty essentially relates to what we do (i.e., how much do we emit). I realise that using “we” is a bit simplistic, since a small fraction of the world’s population dominate the emissions budget, but it’s still clear that future climate change, and what we will have to deal with, depends mostly on future emissions. This is something that we can influence, even if determining how we do so is not a trivial. I also realise that some might argue that the scenario uncertainty is somewhat smaller than indicated in this paper, since some of the scenarios are much less lilely than others. Although true, I don’t think it really changes the basic message.
I have noticed some discussion about how we tend to ignore adaptation over emission reductions. There’s some truth to this, and we will certainly have to develop some adaptation strategies to deal with the changes that are now unavoidable. However, until we get net emissions to ~zero, the climate will continue to change, as will our adaptation strategies. I still think that John Holdren’s comment that [w]e basically have three choices: mitigation, adaptation and suffering. We’re going to do some of each. The question is what the mix is going to be. The more mitigation we do, the less adaptation will be required and the less suffering there will be, is worth bearing in mind.
Partitioning climate projection uncertainty with multiple large ensembles and CMIP5/6, paper by Flavio Lehner et al.
Mitigation, adaptation and suffering – short post by the late Andy Skuce, where I found the John Holdren quote.