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Glen Peters Profile picture
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1 Dec, 8 tweets, 4 min read
This is an interesting figure showing the number of applications of the SSP/RCP framework, by scenario combination.

The darker the shade, the more studies. But, this raises many questions...

1/
nature.com/articles/s4155…
2/ The Shared Socioeconomic Pathways (SSPs) are used as input to Integrated Assessment Models (IAMs) & combined with Shared Policy Assumptions (SPAs) to get different forcing levels (RCPs) in 2100. Earth System Models use pathways generated from the IAM SSP/RCP combinations.
3/ Not all combinations are possible. That is, IAMs often cannot solve for some SSP/RCP combination:
* Only SSP5 can get to RCP8.5 in IAMs
* Many IAMs cannot get to RCP1.9 or 2.6 with SSP3, 4, 5

nature.com/articles/s4155…
4/ Further, a selection of the SSP/RCP combinations were selected for deeper analysis by ESMs in CMIP6 (the blue boxes, the darker blue are higher priority). Based on this, we could expect these blue boxes to be studied more?

gmd.copernicus.org/articles/9/346…
5/ Why is this interesting? Some of the scenarios that are not possible in IAMs have the most applications🤔

SSP2-8.5 has some of the most studies, but no IAM can actually follow that pathway. Presumably impact studies take SSP5-85 & apply SSP2 assumptions to assess impacts?
6/ Lots of runs expected from SSP5-85 & SSP2-45 because of use in CMIP6, but SSP3-70, SSP1-26, & SSP1-19 are not so frequent (maybe no literature yet?).

IAMs are likely to dominate on SSP2 & RCP1.9/2.6, & since they don't, it suggests the literature is dominated by non-IAMs?
7/ After looking at this figure there are many boxes populated that one would not expect. How do people use these SSP/RCPs? Do they know that there is essentially a probability weighting of what is possible & not (based on model solvability)? Do people understand the framework?
8/8 This figure has raised much more than it answers, for me at least... It would be good to see it split by WG1, WG2, & WG3 communities...

Read the discussion in the article, as perhaps it is only me...
nature.com/articles/s4155…

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Glen Peters Profile picture
2 Dec
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)
Read 14 tweets
Glen Peters Profile picture
1 Dec
It is nice to see suggestions for the SSP/RCP framework to include more realistic reference scenarios, building on the work of @hausfath (nature.com/articles/d4158…) & @_neil_grant (nature.com/articles/s4155…) & others

A few thoughts:
1/
 nature.com/articles/s4155…
2/ Does it make sense to include current policies or NDCs across all SSPs? Doesn't the existence of current policies or NDCs begin to preclude some SSPs?

One could use SSP2 (current socioeconomic trends) with scenarios performed with varying SPAs.
3/ This is really a challenge of the SSP/SPA/RCP framework. The three axes are essentially assumed to be independent, this makes theoretical sense but not really practice sense. I understand why that decision was made, but does it make the framework too unrealistic?
Read 8 tweets
Glen Peters Profile picture
30 Nov
1. "Take the example of Shell"

Shell has a "well below 2°C" scenario, but it does this by maintaining high fossil fuel use...

"this logic appears fully internalized in mainstream climate scenarios"

Quotes are from @wim_carton, but thread is based on:
cicero.oslo.no/no/posts/cicer…
2. I looked into how Shell compares to mainstream scenarios in 2017.

Compared to the quantified Shared Socioeconomic Pathways (SSPs, in grey), Shell uses a lot of energy, but the CO₂ emissions are well within the range of mainstream <2°C scenarios RCP2.6.
3. As @wim_carton documents in his paper, Shell uses quite a bit of fossil fuels. A bit more coal than in the average SSP, gas a bit less, oil sort of an average with others with a long tail.

How is it possible to use so much fossil fuel & hit net-zero CO₂ emissions?
Read 7 tweets
Glen Peters Profile picture
27 Nov
En tråd på noen høydepunkter i et intervju med @THEenerWE @HildeNyman på "Det gir ingen mening å se på «worst case scenario»"

1/
enerwe.no/cicero-energip…
Myndigheter bygger på eksisterende politikk, så de trenger å vite hvor vi går med denne politikken, ikke hvor vi hadde gått uten politikk.

2/
Vi trenger mye mer kunnskap om hvilken innvirkning på klima vi kan forvente, ikke mer kunnskap om hvor ille det blir hvis ikke vi gjør noe.

3/
Read 9 tweets
Glen Peters Profile picture
27 Nov
We don't need another decade building more complex models that exploit exascale computing, but one that:
1. Better understands & characterizes fundamental conceptual issues
2. Integrates multi-disciplinary knowledge & perspectives

1/
nature.com/articles/s4146…
Many presume that inadequacies of current models can be solved with more resolution, more detail, more computer.

But, fundamental questions on the inadequacies of models have note been addressed (eg model structure, initial conditions, nonlinear dynamics, etc)

2/
"Climate economists [have] spent decades attempting to provide ever-better numerical estimates of a benefit-cost ratio... Even if the ECS isn’t strictly fat-tailed, the benefit-cost ratio [is] highly sensitive to ... parameters which suffer from deep uncertainty"

3/
Read 5 tweets
Glen Peters Profile picture
26 Nov
The rise of Integrated Assessment Modelling (IAMs) in the climate science-policy interface since 1970.

Why have IAMs become more dominant over time?

1/

sciencedirect.com/science/articl… Image
"...although IAMs aim to function as ‘heuristic guides’ to explore strategies, they are in fact performative: they shape the possibility space in which future options for climate action are discussed & thus the content of policy deliberation in international climate politics"

2/
The authors find five phases representing shifts in the position of IAMs in the climate science-policy interface.

3/ Image
Read 14 tweets

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