There’s a meme in EA that climate change is particularly bad because of a nontrivial probability that sensitivity to doubled CO2 is in the extreme upper tail. As far as I can tell, that’s mostly not real. This paper seems like a very thorough Bayesian assessment that gives 4.7 K as a 95% upper bound, with values for temperature rise by 2089 quite tightly constrained (Fig 23). I’d guess this is an overestimate based on conservative choices represented by Figs 11, 14, and 18. The 5.7 K 95% upper bound after robustness tests comes from changing the joint prior over feedbacks to create a uniform prior on sensitivity, which as far as I can tell is unjustified. Maybe someone who’s better at rhetoric than me should figure out how to frame all this in a way that predictably doesn’t make people flip out. I thought I should post it, though.
For forecasting purposes, I’d recommend this and this as well, relevant to the amount of emissions to expect from nature and humans respectively.
It’s complicated. Searching the article for “structural uncertainty” gives 10 results about ways they’ve tried to deal with it. I’m not super confident that they’ve dealt with it adequately.
Additionally I think it’s not real because if there would be such warming through feedback effects there’s enough time to do heavy geoengineering. Geoengineering has it’s own risks but it’s doable in “runaway warming” scenarios.
There’s a meme in EA that climate change is particularly bad because of a nontrivial probability that sensitivity to doubled CO2 is in the extreme upper tail. As far as I can tell, that’s mostly not real. This paper seems like a very thorough Bayesian assessment that gives 4.7 K as a 95% upper bound, with values for temperature rise by 2089 quite tightly constrained (Fig 23). I’d guess this is an overestimate based on conservative choices represented by Figs 11, 14, and 18. The 5.7 K 95% upper bound after robustness tests comes from changing the joint prior over feedbacks to create a uniform prior on sensitivity, which as far as I can tell is unjustified. Maybe someone who’s better at rhetoric than me should figure out how to frame all this in a way that predictably doesn’t make people flip out. I thought I should post it, though.
For forecasting purposes, I’d recommend this and this as well, relevant to the amount of emissions to expect from nature and humans respectively.
How do they deal with model uncertainty (unknown unknowns)?
It’s complicated. Searching the article for “structural uncertainty” gives 10 results about ways they’ve tried to deal with it. I’m not super confident that they’ve dealt with it adequately.
Additionally I think it’s not real because if there would be such warming through feedback effects there’s enough time to do heavy geoengineering. Geoengineering has it’s own risks but it’s doable in “runaway warming” scenarios.