A History of With 151 Illustrations Springer Thure E. Cerling Atmospheric CO2 and Its Effects on Plants, Animals, and Ecosystems

Our planet’s atmosphere is thought to have changed gradually and over a very wide range of CO2 concentrations throughouthistory. From ancient atmospheric gases trapped in ice bubbles, we have strong evidence indicating that atmo­spheric CO2 values reached minimum concentrations of approximately 180 parts per million during the Last Glacial Maximum, which was only 15,000 years ago. At the other extreme, calculations suggest that some 500+ million years ago the atmospheric CO2 concentrations may have been about 4000 to 5000 parts per million. The available evidence suggests that the decline in atmospheric CO2 over time has been neither steady nor constant, but rather that there have been periods in Earth’s history when CO2 concentrations have decreased and other periods in which CO2 levels were elevated. The changes in atmospheric CO2 concentrations over geological time periods are the result of biological, chemical, and geological processes. Biogeochemical processes play a significant role in removing organic matter from the active carbon cycle at Earth’s surface and in forming carbonates that are ultimately transported to the continental plates, where they become subducted away from Earth’s surface layers.Atmospheric CO2 concentrations rose rapidly as Earth transitioned out of the last Ice Age, and the atmosphere has changed dramatically since the dawn of the Industrial Age with especially large increases over the past five decades. Both terrestrial and aquatic plant life significantly influence the sequestration of atmospheric CO2 into organic matter. There is now substantial evidence to show that these terrestrial and marine photosynthetic organisms currently play a majo