A way to end the world

There is a Scientific American article available on line that presents some compelling evidence that some past extinctions in the earth's history were triggered by green house gasses (CO2) reaching critical levels in the atmostphere. The idea is not that CO2 itself caused the extinctions, but that anomalously increased CO2, which in the case of the extinctions could have been the result of unusual volcanism, triggered the prosperity of certain anaerobic bateria which in turn generate H2S. These bacteria are always present (like, they are out there right now, just waiting), but the suggestion is that under certain conditions they can be productive to the detriment of nearly every other living thing.

The article frets that this mechanism can be triggered for CO2 levels somewhere between 500 and 1000 ppm. As all aficionados of Al Gore and "An Inconvenient Truth" should know, for the last half million years and up until two hundred years ago the maximum CO2 concentration was never greater than 300 ppm. However, thanks to human diligence since the onset of the industrial revolution, it has climbed to 400 ppm, and is continuing to increase at a rate of 2 ppm per year. With no change in our behavior the 500 ppm mark will have been exceeded well before the end of this century. Things could get stinky for our grandchildren and great grandchildren.