“Griffith calculates that, in order to keep the atmospheric concentration of CO 2 at no more than 450 ppm, humanity has to do something that is almost unimaginably difficult. We have to cut our fossil fuel use to around 3 terawatts, which means we have to produce all the rest of our power from non-fossil-fuel sources, and we have to do it in about twenty-five years or it will be too late to level off at 450 ppm.”

“Griffith calculates that, in order to keep the atmospheric concentration of CO 2 at no more than 450 ppm, humanity has to do something that is almost unimaginably difficult. We have to cut our fossil fuel use to around 3 terawatts, which means we have to produce all the rest of our power from non-fossil-fuel sources, and we have to do it in about twenty-five years or it will be too late to level off at 450 ppm.”

— Stewart Brand