Do Plants Prevent Atmospheric CO2 Levels from Falling Too Far?

by Emil Morhardt

A recent paper discussed in the previous post (Galbraith and Eggleston, 2017) claims that during the past 800,000 years when the Earth has been in a glacial condition with the occasional interglacial period (such as now), there is a strong correlation between global temperature and atmospheric CO2 levels, and that they tend to go to the same low point again and again and stay there. These authors argue that if CO2 were to go lower, so would the temperature, and that therefore something is keeping the CO2 level from going any lower then 190 ppm. One intriguing possibility they bring up comes from a paper (Pagani et al., 2009) by Mark Pagani at Yale, and his colleagues at the Carnegie Institution in Stanford and at the University of Sheffield who claim that plants stop effective photosynthesis if CO2 levels fall below 190 ppm, depriving the carbon cycle of two sources of removal of atmospheric CO2; photosynthesis, and a more subtle plant activity called biologically enhanced silicate chemical weathering. The mechanisms of these two processes are interesting. Continue reading