- The concentration of carbon dioxide (CO2) in the atmosphere was 383 parts per million (ppm) in 2007, 37% over pre-industrial revolution concentrations (280 ppm), higher than any concentration over the last 
- The concentration of carbon dioxide (CO2) in the atmosphere was 383 parts per million (ppm) in 2007, 37% over pre-industrial revolution concentrations (280 ppm), higher than any concentration over the last 650,000 years, and “probably” higher than any concentration in the last 20 million years.
- Actual emissions of CO2 over the period of 2000-2007 are higher than the highest (worst-case) IPCC emissions scenario.
- Growth in emissions from cement and coal power plants in developing nations (mostly India and China) now account for more than 50% of all CO2 emissions and a related stagnation in carbon intensity (amount of GDP per unit of carbon).
- The amount of CO2 extracted from the air by natural carbon sinks is rising, but slower than CO2 emissions. In addition, natural carbon sinks have lost efficiency over the last 50 years.
- The GPC concludes that all of the above combine to produce stronger CO2-driven climate forcing, and sooner than the IPCC estimates.
So, then, what does this all mean?
First off, this means we need to start decarbonizing human civilization sooner, decarbonize faster, and decarbonize to an even lower level than the IPCC AR4 target (emissions peaking between 2015 and 2020 and 50% below 1990 levels by 2050). The worst-case IPCC-SRES scenario has humanity dumping about 2,500 Gt more carbon into the atmosphere than 1990 levels by 2100, and we’re now running above that worst-case scenario. For reference, the 383 ppm of CO2 in the Earth’s atmosphere currently represents about 812 GtCO2, or about 221 GtC. 2,500 GtC represents an 11x increase in CO2 concentration, or 4,328 ppm – 0.4% of the atmosphere – by 2100. CO2 hasn’t been that high since between 50 and 60 million years ago, when mammals began to take over from the ex