I don't see the methane feedback loop in there. It is the one that either will or is now, self perpetuating, and will lead to much higher temperatures, much quicker. It may take another hundred years or more before the ELE is complete. One thing they do say is that even with a 90% drop in CO2 emissions, the 2*C point will be reached. If we are not at the methane self-sustaining release level, we will then for sure.
People could have reduced population and reduced impact, if they had done it in time. The sustainable level has been accelerating in its fall since the early 1990s and is probably at around 2/3 billion at a Euro standard of living, while the Earth's human population is 6.7 billion. 10 times sustainable is a lot of overshoot. With a reduction immediately to sustainable by some war or disease, there is still that momentous rise to the self sustaining methane/CO2 feedback loop and mass extinction. The time to reduce population by forced programs is passed. China never reached the magic number of TFR=1. They are the only ones who gave it a try, with authoritarian rule, and it still did not work. Now the "cure" is as bad as the "disease", and still will not stop ELE. The average human was just not intelligent enough of a creature to learn to live sustainably.
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