Carbon dioxide concentration hit 400 ppm this spring at a NOAA Monitoring Station in Barrow, Alaska. The remoteness of the location ensures a measurement without the confounding factors of localized CO2 emissions (for example, from heavy traffic). It is safe to say that the global average CO2 concentration is now at approximately 400 ppm, way beyond the “safe” threshold of 350 ppm. We are now entering the world of potentially catastrophic climate change. We can’t stop the change, but human society is still in a position to affect the severity of the impacts. I’m pessimistic about how long we will remain in this position.
Carbon dioxide is not the only greenhouse gas. NOAA calculates the Annual Greenhouse Gas Index every year, which takes into account the heating effects of other gases that are emitted from human activities (e.g., methane, nitrous oxide, and chemicals called chlorofluorocarbons). When those gases are also considered, the global atmosphere reached a CO2 equivalent concentration of 400 ppm in 1985; and 450 ppm in 2003. Atmospheric CO2 levels are currently higher than they have been at any time during the last 800,000 years.