by Donn Dears, July 2017

Here is a summary of the graph’s salient points:

• The CO2 safe limit for US Navy submarines is 8,000 ppm (Dotted red line)
• The CO2 safe limit for the space station is 5,000 ppm (Dotted blue line)
• A line depicting the gradual doubling of CO2 is near the bottom of the graph
• The minimum atmospheric CO2 requirements to sustain plant growth is 150 ppm (Dotted green line)

In addition, atmospheric CO2 has been as high as 7,000 ppm approximately 550 million years ago, and as high as 2,000 ppm as recently as 150 million years ago. (Also here in French)

What the graph clearly shows is how close mankind came to extinction when atmospheric CO2 levels dropped to 183 ppm during the last ice age.