Another data point that keeps popping up in climate science is the global atmospheric CO2 concentration, which currently is around 415 parts per million (ppm). The IPCC report that was published yesterday didn’t say anything new about the 450 ppm threshold and it remains to be seen if the upcoming deliverables from working groups II and III will have anything to say about it. Whether of not 450 ppm is the correct threshold number is, however, not the main point. The point is that there’s a clear link between global warming and atmospheric CO2 concentration.