With regard to my comment at hypergeometric | July 13, 2016 at 3:50 pm on Tamino’s blog, someone challenged me on my assertion “Believe me, the +3C-+4C worlds are not places we want to go!” there. I have replied at Tamino’s blog, and I recommend reading the excellent comments there for context, but I thought it worthwhile to state my position here as well. Below is the quote. And we are apparently heading to the +3C to +4C region, even if COP21 is fully implemented. (See NCAR’s full report.)
While a detailed substantiation is inappropriate for this space, I’ll just mention three:
- a World Bank report on the risks of a +4C degree world
- The 2013 paper by Caballero and Huber indicating Eocene warming for atmospheric CO2 concentrations comparable to those we may see in the next 100 years and based upon paleoclimate records was +13C +- 3C warmer than today, not merely +4C
- An introduction to and interpretation of Caballero and Huber by Ray Pierrehumbert (“Hot climates, high sensitivity”) in terms of non-linear, state-dependent climate sensitivity, described there as a Figure 1
The basis for my assertion is that we definitely do not want to approach the region [Professor] Ray [Pierrehumbert] writes “Here there (may) be dragons.”
While I am not a climate scientist, I am enough of a dynamicist to look at the rate with which we are introducing greenhouse gases compared to natural processes we can read in the paleorecord (with the possible exception of the Permian extinction event) to wonder whether or not we are actively exploring the climate state space for dynamical bifurcations. People who have examined the question suggest we would probably never know if we were approaching one. While there’s little that can be done except to press on for rapid reductions in CO2 emissions, I can only be honest and say these realizations make me very nervous.
Update, 2016-07-16
From Richard Pauli. See his blog for more.
ecoquant
667 per centimeter : climate science, quantitative biology, statistics, and energy policy 
I think your comment was excellent. Especially how a proper timetable requires governmental policy intervention. Which is another reason I do not like the carbon tax – it doesn’t actually do anything (except make people hate environmentalism) As Doc Snow himself pointed out without seeing what he was saying:
“. Even if they hate the idea of shifting away from FF use, they will end up doing so, because the carbon embodied in the goods they buy will tend to decrease over time.”
“Tending to decrease over time is a prescription for timetable disaster. Plus, why have a plan that makes people “hate shifting away from fossil fuels”?1?
People will LOVE shifting away from fossil fuels is they save a ton of money doing so. A few years worth of national FF spending could be buying us a brand new Free Electricity machine that every year will put about $3200 for every person in the household back into the checking account. Oy yeah – it will also solve AGW and save society quatrillions and save millions of species.
We can either eat or cake and have it too, or we can sit on our hands and watch laissez-faire capitalists nibble at the edges of the problem until the apocalypse consumes us all.