James Hansen and the Three Categories of the Runaway Greenhouse

[OKIsItJustMe]

15. Yes, but…

Remember Hansen’s earlier work, in which he suggested aiming for 350 ppm of CO[font size="1"]₂[/font] in the atmosphere (as a start.)

http://arxiv.org/abs/0804.1126

[font face=Serif][font size=3]… If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO[font size="1"]₂[/font] will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that. The largest uncertainty in the target arises from possible changes of non-CO[font size="1"]₂[/font] forcings. An initial 350 ppm CO[font size="1"]₂[/font] target may be achievable by phasing out coal use except where CO[font size="1"]₂[/font] is captured and adopting agricultural and forestry practices that sequester carbon. If the present overshoot of this target CO[font size="1"]₂[/font] is not brief, there is a possibility of seeding irreversible catastrophic effects.

…[/font][/font]

(Emphasis added by me.)

Avoiding the levels of emissions presented in this later paper is not sufficient.