Re: "Obviously, AR5 climate scientists were most likely ignoring cumulative ECS risk mechanisms "
I will disagree. AR5 (as is happening in AR6) scientists are tasked to put together literature review of current science. They are not asked for their opinions on the literature, peer review occurs before publication. Accusing them of ignoring relevant literature is something I will not do, since I have no evidence. In the case of MICI, The Bassis and Walker paper came after the deadline for AR5.
sidd
I note that this forum is filled with tens of thousands of post documenting observed climate change's damaging impacts, yet there are virtually no significant carbon pricing programs implemented by world governments to date. In my opinion this is partially due to the fact that AR5 issued a carbon budget based on left-tail assumptions about climate sensitivity including about ice-climate feedback mechanisms. The AR5 carbon budgets (written by consensus climate scientists) tell decision makers that they have decades of time before it is too late to stay well below the 2C GMSTA target. However, the two associated linked articles (parts 1 & 2); demonstrate that when the risks (probabilities times consequences) associated with worse plausible cases are considered, even very high social costs of carbon, SCC, are justified to be added to the prices of fossil fuels (preferably together with a UBI, or dividend, program).
Title: "On Buying Insurance, and Ignoring Cost-Benefit Analysis"
http://triplecrisis.com/on-buying-insurance-and-ignoring-cost-benefit-analysis/Extract: "The damages expected from climate change seem to get worse with each new study. Reports from the IPCC and the U.S. Global Change Research Project, and a multi-author review article in Science, all published in late 2018, are among the recent bearers of bad news.
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In fact, a crash program to decarbonize the economy is obviously the right answer. There are just a few things you need to know about the economics of climate policy, in order to confirm that Adam Smith and his intellectual heirs have not overturned common sense on this issue. Three key points are worth remembering.
For uncertain, extreme risks, policy should be based on the credible worst-case outcome, not the expected or most likely value. This is the way people think about insurance against disasters.
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As the careful qualifications in the IPCC and other reports remind us, climate change could be very bad, surprisingly soon, but almost no one is willing to put a precise number or date on the expected losses.
One group does rush in where scientists fear to tread, guessing about the precise magnitude and timing of future climate damages: economists engaged in cost-benefit analysis (CBA).
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The disastrous worst-case risks are all on the benefits, or avoided climate damages, side of the ledger. The scientific uncertainties about climate change concern the timing and extent of damages. Therefore, the urgency of avoiding these damages, or conversely the cost of not avoiding them, is intrinsically uncertain, and could be disastrously large."
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Title: "Climate Damages: Uncertain but Ominous, or $51 per Ton?"
https://skepticalscience.com/climate-damages-51-per-ton.htmlAbstract: "According to scientists, climate damages are deeply uncertain, but could be ominously large (see the previous post). Alternatively, according to the best-known economic calculation, lifetime damages caused by emissions in 2020 will be worth $51 per metric ton of carbon dioxide, in 2018 prices.
These two views can’t both be right. This post explains where the $51 estimate comes from, why it’s not reliable, and the meaning for climate policy of the deep uncertainty about the value of damages.
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The “social cost of carbon” (SCC) is the value of present and future climate damages caused by a ton of carbon dioxide emissions.
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Expected climate damages are uncertain over a wide range, including the possibility of disastrously large impacts. The SCC is a monetary valuation of expected damages per ton of carbon dioxide. Therefore, SCC values should be uncertain over a wide range, including the possibility of disastrously high values.
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As explained in the previous post in this series, deep uncertainty about the magnitude and timing of risks stymies the use of cost-benefit analysis for climate policy. Rather, policy should be set in an insurance-like framework, focused on credible worst-case losses rather than most likely outcomes. Given the magnitude of the global problem, this means “self-insurance” – investing in measures that make worst cases less likely.
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In short, we already know that doing everything on the least-cost emission reduction path will cost less, per ton of carbon dioxide, than worst-case climate damages.
That’s it: end of economic story about evaluating climate policy. We don’t need more exact, accurate SCC estimates; they will not be forthcoming in time to shape policy, due to the uncertainties involved. Since estimated worst-case damages are rising over time, while abatement costs (such as the costs of renewables) are falling, the balance is tipping farther and farther toward “do everything you can, now.” That was already the correct answer some years ago, and only becomes more correct over time."
ASLR