from the blog of Joseph Romm, author of Hell and High Water…
Hansen (et al) must read: Get back to 350 ppm or risk an ice-free planet
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Also, if I am reading Hansen et al correctly (and Lord knows I may not be), then I think he may be mostly right for a different reason than he thinks, which is to say, I think the carbon-cycle feedbacks (including the tundra melting and sink saturation) act as the equivalent of the amplifiers that he models (”loss of Greenland and Antarctic ice and spread of vegetation over the vast high-latitude land area in the Northern Hemisphere” — I will come back to that vegatation issue in a future post). In other words, if you get near 450 ppm and stay there for any length of time, you will shoot up to 700 to 1000 ppm, which certainly gets you an ice-free planet. Or perhaps the simplest way to put this — the IPCC is right when it says:
We’re at 8 GtC/yr and rising 3% annually. We need to average below 5 GtC/yr — and maybe considerably less — for the whole century to avert catastrophe. We need to be near zero or below by 2100.
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