Thread by @Peters_Glen

1/ "the availability of BECCS proved critical to the cost-efficiency, & indeed the theoretical possibility, of these deep mitigation scenarios, leading to systemic inclusion of BECCS in RCP2.6 scenarios" says @katedooley0, Christoff, @KA_Nicholas

cambridge.org/core/journals/…

2/ "The incorporation of NETs in IPCC scenarios is one clear illustration of how, as @EstherTurnhout put it, “dominant political discourses compel scientists to create assessments that work within these discourses”..." writes @wim_carton

researchgate.net/publication/34…

3/ I know people don't like these sorts of statements. They illustrate that 1.5°C, even <2°C, are considerably harder without large-scale CDR.

If we take CDR out of IAMs, then very few will be able to reach deep mitigation pathways. (there are some buts, to follow)

4/ Sure, there are scenarios like LED (which still uses large-scale afforestation), which shift feasibility to demand side issues (nature.com/articles/s4156…)

You could argue then, that if we exclude technical CDR, we just shift discussion from crazy BECCS to crazy demand side?

5/ There are deeper issues here. The white boxes are elements not included in IAMs.

IAMs all include BECCS, but many don't include advanced nuclear or synthetic fuels or... Very few demand side measures are included in most IAMs.

ipcc.ch/sr15/

6/ The excessive use of CDR in IAMs has meant there has been a spotlight on CDR & the narrative CDR is "necessary".

There has been less spotlight on what is not included in IAMs or why IAMs preferentially seem to follow high CDR pathways.

7/ In this sense, there is a clear argument that IAMs have been performative. They have framed the climate debate, the technologies we consider, the discussions we have, even what a pathways looks like (or "has" to look like).

cambridge.org/core/journals/…

8/ We are all now 'trained' to think CO₂ emissions must be negative in 2100, & all scenarios have to be peak & decline (overshoot) scenarios. We struggle to see alternatives, because the alternatives are swamped by the standard.

9/ The reason we have these peak & decline scenarios goes back 10+ years. IAMs struggled to get to 450ppm without first exceeding 450ppm.

The climate target was shifted to 2100 instead of "not-to-exceed" any time, just so IAMs could find a solution!

sciencedirect.com/science/articl…

10/ Now, nearly all scenarios are based on 2100 targets, which also has a nice theoretical economic rationale (Hotelling Rule).

But, a 2100 target is a value judgement, rarely known by anyone other than IAMers. It matters too.

iopscience.iop.org/article/10.108…

11/ These things are all well-known by IAMers, it is bread & butter for them. They have huge trust & respect through, eg, the IPCC process. Critiques are therefore outsiders, pushing against the mainstream & established science.

sciencedirect.com/science/articl…

12/ If you push back on any of this, or try & do alternative scenario, it is a constant battle. "What about those 1000 scenario assessed by the IPCC, why do we need more scenarios" 🤦

This just slows the inevitable down!

13/ IAMers eventually get to some of the issues raised: low energy demand, discount rates, high renewables, alternative scenario designs, etc, but it all comes 5 years slower than it needs to (IMHO).

14/ Ok, that thread went on more of a tangent then I had originally planned. I guess I am trying to reflect that critiques are not just random, people have actually thought through many issues, read literature, etc.

Now, to work...

/end