ATTP started it by posting on Well below 2 °C: Mitigation strategies for avoiding dangerous to catastrophic climate changes by Yangyang Xua and Veerabhadran Ramanathan. But as you can tell from ATTP’s post, the principal question – although he is far too polite to put it so bluntly – is “where’s the novelty?”1 All their GHG and temperature scenarios, as they themselves stress, are consistent with IPCC; so there’s nothing new there. Neither are the stochastic runs and attempts to assess the probabilities of exceeding various thresholds. Neither, alas, are the attaching of arbitrary labels to arbitrary temperature thresholds, although this is without doubt the bit that will interest the meeja.
FWIW, I think that 3oC GW is certainly “dangerous”, though I’d be hard pressed to assign a clear meaning to the term.
I could try reading their PR which confirms my suspicions: A new study evaluating models of future climate scenarios has led to the creation of the new risk categories “catastrophic” and “unknown” to characterize the range of threats posed by rapid global warming. I think that really does mean tht the labels are the novelty. They continue, Researchers propose that unknown risks imply existential threats to the survival of humanity which is either meaningless or vacuous, I can’t quite tell which.
While I’m here, I’ll quote Climate risks can vary markedly depending on the socioeconomic status and culture of the population… the poorest 3 billion people living mostly in tropical rural areas, who are still relying on 18th-century technologies for meeting basic needs such as cooking and heating… mostly subsistent farmers, whose livelihood will be severely impacted, if not destroyed, with a one- to five-year megadrought, heat waves, or heavy floods… But the article errs, I think, in not considering possible changes to this population. Certainly the proportion, and absolute number, of people living in absolute poverty has decreased over the last 50 or 100 years, and can be expected to continue to decrease, especially or almost entirely if their governance improves; see-also Harvey. That doesn’t help the ecosystems, of course. But the West has entirely removed the class of “subsistence farmers”2; everyone else will follow suite in due course.
1. Yes I know it’s ironic, isn’t it?
2. That’s someone, errm, telological, perhaps. No-one called “the West” decided to remove this class of people. But “the West” provided the kind of society in which no-one wanted to be a subsistence farmer, and no-one had to be if they didn’t want to be.
3. Picture: panel in font, Vallouise.
* rump administration loosens Obama’s guidelines for self-driving cars: States are advised against setting up too many regulations; the Verge.
* How A Warm Winter Destroyed 85 Percent Of Georgia’s Peaches – 538.
* Economics says time to shut down some coal plants (even ignoring externalities) – Brian at Eli’s.