I don’t think this changes the fundamental conclusion, but there are a couple of choices here that seem to make this imbalance larger than it really is:
The Wagner and Weitzman probabilities are pre-Paris-Agreement era and newer estimates would probably put quite a bit lower probability on extreme warming levels (e.g. see here).
Because policy targets are focused on 1.5 and 2 degrees, a lot of sections of the IPCC report will study those scenarios more, whereas the real concern seems the understudy of climate impacts (the problem is not that we don’t have enough IAMs showing us how to get from 4 to 3.5 degrees but that we don’t understand well what 3.5 and 4 degree worlds look like, right?). If that is right, it seems a bit surprising you are looking at entire IPCC reports rather than only the relevant working groups.
We settled on Wagner and Weitzman because it is well known and also because they were kind enough to provide us with their data and code. It is indeed true that other probability curves might paint a more optimistic picture. However, the differences are so large that I would be surprised if it would change the conclusion of our paper.
We looked at the complete IPCC reports, because we wanted to understand the overall focus of policy relevant research. But it is indeed true that the research gap differs between the working groups and the research gap is larger when it comes to the impact focused reports.
Thanks for that paper Johannes, it was mildly reassuring to read.
Liu and Raftery (2021) show that countries must increase their decarbonization rates by 80% relative to Paris commitments to limit warming to 2°C by 2100. Similarly, if the pace of global decarbonization fails to keep up with IEA’s (2020) STEPS projections (decarbonization has exceeded IEA projections in recent years; see IEA 2019, 2020), we find that several scenarios having greater than 3°C warming by 2100 become plausible (Fig. S4B).
One thing I was struck by is this section in the discussion (bold emphasis mine) is that an 80% increase in decarbonisation rates relative to Paris commitments seems quite large and slightly ironically, not very plausible. Is there any evidence that countries are making or planning to make such a radical step up in their decarbonisation, as it seems like their policies don’t even reflect this?
Paris Agreement targets are till 2030, so I’d be less deterministic wrt what is possible till 2100, looking at Liu and Raftery it sounds as though they are just extrapolating current trends.
In worlds where we would keep temperature <2C by 2100, I would expect large structural breaks, not getting there by trend extrapolation/incremental steps (e.g. decarbonization getting really cheap and easy at some point, or negative emissions becoming very affordable and scaleable etc.).
Cool stuff!
I don’t think this changes the fundamental conclusion, but there are a couple of choices here that seem to make this imbalance larger than it really is:
The Wagner and Weitzman probabilities are pre-Paris-Agreement era and newer estimates would probably put quite a bit lower probability on extreme warming levels (e.g. see here).
Because policy targets are focused on 1.5 and 2 degrees, a lot of sections of the IPCC report will study those scenarios more, whereas the real concern seems the understudy of climate impacts (the problem is not that we don’t have enough IAMs showing us how to get from 4 to 3.5 degrees but that we don’t understand well what 3.5 and 4 degree worlds look like, right?). If that is right, it seems a bit surprising you are looking at entire IPCC reports rather than only the relevant working groups.
We settled on Wagner and Weitzman because it is well known and also because they were kind enough to provide us with their data and code. It is indeed true that other probability curves might paint a more optimistic picture. However, the differences are so large that I would be surprised if it would change the conclusion of our paper.
We looked at the complete IPCC reports, because we wanted to understand the overall focus of policy relevant research. But it is indeed true that the research gap differs between the working groups and the research gap is larger when it comes to the impact focused reports.
Thanks for that paper Johannes, it was mildly reassuring to read.
One thing I was struck by is this section in the discussion (bold emphasis mine) is that an 80% increase in decarbonisation rates relative to Paris commitments seems quite large and slightly ironically, not very plausible. Is there any evidence that countries are making or planning to make such a radical step up in their decarbonisation, as it seems like their policies don’t even reflect this?
Paris Agreement targets are till 2030, so I’d be less deterministic wrt what is possible till 2100, looking at Liu and Raftery it sounds as though they are just extrapolating current trends.
In worlds where we would keep temperature <2C by 2100, I would expect large structural breaks, not getting there by trend extrapolation/incremental steps (e.g. decarbonization getting really cheap and easy at some point, or negative emissions becoming very affordable and scaleable etc.).