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I've seen this 'scientists warning' video claiming that 10C of warming is possible within 20-30 (or even 10!) years go round before. I resisted covering it, but now it’s being reboosted by Counterpunch & Roger Hallam (of XR). Needless to say, it's not accurate - here's why: 1/8 https://twitter.com/RogerHallamCS21/status/1264193908961153025
The first claim for+10C (~3:09 in the video) is that Hansen et al (2016) put climate sensitivity at 10C per 2xCO2. But this is a misreading of the paper ( https://www.atmos-chem-phys.net/16/3761/2016/acp-16-3761-2016.pdf) - 10C is cherry-picked from halfway through a footnote calculation which concludes an ECS of ~4C. 2/8
Climate sensitivity also can’t be used like this – ECS tells us how much warming to expect from 2xCO2 in a century+, and so even if ECS were 10C (which is *far* outside the current 1.5-4.5C IPCC range, or even recent hi-ECS models) warming would take much longer than 20-30y. 3/8
The second claim for +10C (at ~5:08) is a bar chart from (notoriously unreliable) arctic news blogspot, suggesting that rapid feedbacks can add up to 10C. But all the numbers are far above literature values, with limited justification provided in the original blogpost
. 4/8
. 4/8
Links on each claim: current warming ( https://climatetippingpoints.info/2019/10/14/fact-check-will-2c-of-global-warming-trigger-rapid-runaway-feedbacks/#June2019_2degrees), shifted baseline ( https://climatetippingpoints.info/2019/04/15/fact-check-do-tipping-points-and-feedbacks-commit-us-to-rapid-catastrophic-warming/#preindustrial_baseline_check), aerosol dimming ( https://climatetippingpoints.info/2019/04/15/fact-check-is-global-dimming-shielding-us-from-catastrophe/), arctic albedo ( https://climatetippingpoints.info/2019/04/02/fact-check-will-an-ice-free-arctic-trigger-a-climate-catastrophe/#blueoceanevent), arctic methane ( https://climatetippingpoints.info/2019/05/13/fact-check-is-an-arctic-methane-bomb-about-to-go-off/#ESAS_Bomb), vapour feedbacks ( https://climatetippingpoints.info/2019/04/15/fact-check-do-tipping-points-and-feedbacks-commit-us-to-rapid-catastrophic-warming/#water_vapour_feedback_check) 5/8
The speaker & article also gives +4C as a definite cutoff for human extinction. A 4C World would be *terrible*, likely with significant areas uninhabitable without A/C, millions of deaths, and many more suffering, but there’s no evidence for possible extinction at this point. 6/8
The article says that this “thesis need not be 100% correct”, but the +10C claim is *far* from 100%. Climate feedbacks will make limiting warming more difficult, but the evidence shows that they still pale in comparison to direct human emissions: https://climatetippingpoints.info/2019/04/15/fact-check-do-tipping-points-and-feedbacks-commit-us-to-rapid-catastrophic-warming/. 7/8
Summary: There’s no way the Earth could warm 10C in 1-3 decades from human emissions plus climate feedbacks alone, and I don’t think it’s any way helpful to boost such baseless scenarios. Human emissions are by far still the dominant driver of warming, & need to fall ASAP. 8/8
