Our letter focuses on CARB's approach for managing uncertainty and risk on the path to California's ambitious 2030 climate target. As we point out, the scoping plan process began at a time when California could expect a cooperative federal government. With the Trump Administration moving to reverse the United States' early efforts on climate, however, a number of key provisions in the proposed scoping plan are now at risk.
Mason and Mike did a remarkable job of using CARB's own data and models to analyze the impacts of the Trump Administration's actions two key policy areas: (1) EPA's review and possible revocation of California's Clean Air Act waiver authority to exceed federal regulations for emissions from light-duty vehicles, and (2) increased hydrofluorocarbon (HFC) emissions as a result of the U.S. Senate not ratifying the Kigali Amendment to the Montreal Protocol. Mason and Mike each contributed an extensive technical appendix showing how these calculations were made, in order to help CARB staff evaluate the risks with greater clarity.
Our modeling work suggests that worst case outcomes in each instance could cause emissions to exceed the scoping plan goal by 52 MMtCO2e (vehicles waiver) and 51 MMtCO2e (Kigali Amendment) above the scoping plan goal, expressed as cumulative emissions over 2021-2030 using 100-year AR4 GWPs. Together, the risks clock in at 103 MMtCO2e, which is about 15% of the cumulative emissions reduction budget (680 MMtCO2e) CARB is using to establish compliance with SB 32's target for 2030. (As an aside, it still isn't clear how a cumulative emissions budget can be used to demonstrate compliance with an annual target, but that's another problem.)
The implication of these risks is that if they come to pass—and the loss of the Kigali Amendment looks very likely at this point—other policies will likely need to pick up the slack in the final scoping plan. One option would be to shift these planned reductions to the cap-and-trade program (although I should point out that cap-and-trade needs a 2/3 re-authorization vote in the Legislature). In that case, the projected role of the cap-and-trade program would grow from 191 to 294 MMtCO2e over 2021-2030, an increase of 54%. As this calculation shows, incorporating policy risks into the scoping plan highlights the importance of getting a robust carbon pricing program in place for the post-2020 period.
In addition to quantifying the potential impacts from hostile federal policy, we also point out that CARB's use of a deterministic reference case to analyze business-as-usual emissions to 2030 introduces significant uncertainty into the planning process. No single forecast can serve as a reliable basis for planning on this time horizon; by locking into a single reference scenario without any uncertainty analysis, CARB would increase the risk of strategic errors in its efforts to achieve deep decarbonization.
I'm really proud of this letter as an example of what can be accomplished by merging legal analysis with high-quality technical modeling. Great job, everyone!