It’s something I hadn’t thought about, but it’s a question provoked by being asked what is the present concentration of CO2 in the atmosphere and what was it 150 million years ago, in the middle of the period when the dinosaurs roamed the Earth. The answers are for me very interesting.
What percentage of the atmosphere is CO2? Well I thought it must be something like 5 or 10%! No, it’s actually 400ppm or, 0.4%!
Plants actually die if the level of CO2 in the atmosphere drops too much, it it gets down to around 250ppm or 0.25% they stop photosynthesis and start to die! Plants thrive in much higher CO2 concentration, their ideal is around 3000ppm or 3%. They also become more drought hardy!!
Finally, in the middle of the era when the largest animals to ever exist were plodding around, in a lush green environment the level of CO2 was over 3000ppm or 3%, the ideal levels for plants! and 750% higher than today.
So, when I hear about thermal runaway of the atmosphere, we are all doomed, it seems rather strange when the world not only survived but thrived with massively higher CO2 levels. Why doesn’t this ever feature when we talk about climate change?