Thread by @Peters_Glen

"Since IAMs are designed to minimize mitigation costs, this means that they by definition select for the most gradual reduction in fossil fuel use."

A thread on 'gradualism' based on @wim_carton's article

https://twitter.com/wim_carton/status/1328965927250046980

2/ "As the IPCC points out, aggregate mitigation costs in IAMs generally increase when action is delayed. ... The longer mitigation is delayed, ... the more investments and/or devaluations it will therefore take to eventually bring emissions down to net zero/net negative."

3/ "The cost of mitigation is therefore not a function of continued fossil fuel use per se, but of the steepness of the mitigation curve, that is, of how quickly fossil fuel consumption needs to fall in order to reach the specified temperature target."

4/ "Including CCS in IAMs essentially decouples fossil fuel consumption from emissions, and therefore allows the former to fall more slowly relative to the latter."

5/ "Negative emissions go even further in that they actually extend the carbon budget and thus stretch out the emission reduction curve itself. The effect is to reduce the rate at which fossil fuel use needs to fall, which in turn leads to lower mitigation costs."

6/ Here is a passage of text from @DetlefvanVuuren. Detlef, this still the case (or accurate), it is from a 2007 article link.springer.com/article/10.100…

7/ Elmar Kriegler is also quite direct: "The value of [Carbon Dioxide Removal] lies in its flexibility to alleviate the most costly constraints on mitigating emissions." link.springer.com/article/10.100…

8/ A technology that is not known to be cheap (BE/FFCCS) & too costly to deploy now, is the technology which "alleviates the most costly constraints". Basically, it is not the cost of BE/FFCCS, per se, but other costs in the system which matter most.

9/ [I think we obsess too much about technology costs, & don't think enough about the way costs are formulated in an optimisation model, which will depend on the binding constraints]

10/ "IAMs generally use a discount rate of 5%, which means they weigh costs and benefits in the present more heavily than those that will occur in the future."

11/ "reducing the discount rate from 5% to 2% would more than double today's carbon price & more than halve the carbon budget overshoot, corresponding to a reduction of about 300 GtCO2 of net negative emissions over the century." iopscience.iop.org/article/10.108…

12/ One parameter, the discount rate, is quite critical to the outcome. But, there is very little sensitivity analysis done on the discount rate (in mitigation analysis, it is done a lot on cost-benefit analysis).

[This is *one* parameter, out of thousands]

13/ I think this is the most important section of @wim_carton's paper, as it tries to dig into why the mainstream framework of scenario analysis might lead to more CDR (& more fossil fuels).
researchgate.net/publication/34…
/end