Comment 500 means statistically significant health effect (Score 4, Interesting) 135
When CO2 gets above about 500ppm, you'll start to see statistically observable health effects in humans. People who are more susceptible to CO2 toxicity will feel drowsy, run-down, and complain that air quality is noticeably poor. At 1000ppm, about 50% of humans will begin showing these symptoms. At this rate, we'll see 1000ppm in the next century, and maybe faster as America tries so hard to make itself great again.