Historic Low of sub 400 ppm CO2 Levels Shouldn t it be mentioned somewhere that at 380 ppm today we are at an historic low of CO2 concentrations when we look back at past CO2 levels The only other time CO2 has dropped below 400 ppm has been the late Carbiniferous some 300 million years ago but at all other times CO2 has been above 400 ppm The graph here shows CO2 levels with a black line and temperature is the blue line In fact it s been as high as 7000 ppm during the Cambrian period which was so favorable to life that it resulted in the famous Cambrian Explosion an explosion of biodiversity This seems to contradict the predictions that our 380 ppm level will result in dire consequences for life It s a basic crime of omission by leaving these facts out