There is a bombshell buried in the middle of the IPCC report. So far, it hasn’t received the attention it deserves. In a bullet point on the bottom of page twelve, the report says that dangerous feedback mechanisms are a ticking timebomb, and require dramatic action now.

Translated into plain English, they are saying that we need to reduce our greenhouse gas emissions far more than previously expected — up to 27% more — or else it will be impossible to deal with global warming because of feedback mechanisms. This is one of the central premises of my book Hell and High Water, and there was little indication it was going to be in the report. It is a meaningful addition.

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The key bullet from the report (bottom of page 12):

Climate-carbon cycle coupling is expected to add carbon dioxide to the atmosphere as the climate system warms, but the magnitude of this feedback is uncertain. This increases the uncertainty in the trajectory of carbon dioxide emissions required to achieve a particular stabilisation level of atmospheric carbon dioxide concentration. Based on current understanding of climate carbon cycle feedback, model studies suggest that to stabilise at 450 ppm carbon dioxide, could require that cumulative emissions over the 21st century be reduced from an average of approximately 670 [630 to 710] GtC to approximately 490 [375 to 600] GtC. Similarly, to stabilise at 1000 ppm this feedback could require that cumulative emissions be reduced from a model average of approximately 1415 [1340 to 1490] GtC to approximately 1100 [980 to 1250] GtC. {7.3, 10.4}

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