One of the most pressing messages that climate scientists attempt to convey to the public is how today’s CO2 levels compare to those of the Geologic past. Such comparisons can provide public context for current CO2 rise, as well as important information on the response of global temperatures to rising CO2. A new study published in Geology suggests that present-day CO2 levels (412 ppmv) are now likely higher than at any time in at least the last 23 million years!
In this newly published study, a team led by Brian Schubert, Associate Professor in the School of Geosciences at the University of Louisiana at Lafayette, used the remains of dead plants to produce a new record of atmospheric CO2 that spans 23 million years of uninterrupted Earth history. Their findings relied on the nearly continuous record of terrestrial photosynthesis provided by organic matter accumulated from partially decomposed plants.
“When plants grow, the relative amount of the two stable isotopes of carbon, carbon-12 and carbon-13, changes in response to the amount of CO2 in the atmosphere,” says Schubert. “One can therefore measure the relative amount of these two isotopes and calculate the CO2 concentration under which the plants grew.”
The remains of land plants can be used to calculate the amount of CO2 in Earth’s atmosphere. Photo credit: A. Hope Jahren