Thread by @RogerPielkeJr

🚨New Preprint posted🚨

Most plausible 2005-2040 emissions scenarios project less than 2.5°C of warming by 2100
osf.io/preprints/soca…
w/ @matthewgburgess @jritch

What do plausible IPCC scenarios project to 2100?
We answer this question
And the news is good

🧵 follows...

We have done a lot of work to identify implausible scenarios of the future
➡️iopscience.iop.org/article/10.108…
➡️sciencedirect.com/science/articl…

In this new paper we turn that around and seek to identify plausible scenarios and analyze them as a subset of all scenarios

Plausibility as a criteria to evaluate scenarios comes from IPCC

We define plausibility as an acceptable growth rate error in CO2 emissions 2005-2020 & 2005-2040

We use 2 error filters with 1311 AR5 & SSP scenarios identifying the 5-10% & 20-40% most plausible scenarios ⬇️

Here you can see the envelope of plausible scenarios overlaid on all 1311 scenarios

The plausibility filter does not make much difference at the top end - both top out at <50 Gt CO2 to 2100

The low end is a bit lower for the less stringent filter

You will want to look at this figure for a little bit, I think it is amazing

It shows how ridiculous current baseline scenarios are & also shows most plausible scenarios center on SSP3.4 outcomes (and that's good news!)

The subset of plausible scenarios project continued climate policy implementation -- so there is a lot of work to do

But they collectively indicate that the world in 2021 is much better positioned to take on this challenge (and it is a challenge) than conventionally assumed

The plausibility of negative CO2 technologies has been questioned
Neg CO2 is central to most of our plausible scenarios
So we stripped out the negative emissions and our conclusions still hold
The plausible scenarios illustrate the importance of neg CO2 to policy success

For fellow nerds we also decompose the plausibility analysis by Kaya factors & all looks solid (except pc GDP, which we documented in Burgess et al 2020: iopscience.iop.org/article/10.108…)

Here are our conclusions

One big question is metaphysical: Does this analysis say something meaningful about our collective future, just about how we think about that future or both?

Taking IPCC scenarios seriously, this analysis is welcome good news, but much work remains

Please see my colleague @matthewgburgess excellent thread on the paper here:

https://twitter.com/matthewgburgess/status/1374737849094922241?s=20

We welcome your feedback and comments before we submit

I for one think this is an important analysis, given how central IPCC scenarios are to research and policy
/END