Mass Extinctions and Their Relationship With Atmospheric Carbon Dioxide Concentration: Implications for Earth's Future

Abstract

Industrialization has raised the concentration of carbon dioxide (CO2) in Earth's atmosphere by half since 1770, posing a risk from ocean acidification to global biodiversity, including phytoplankton that synthesize approximately (∼) 50% of planetary oxygen. This risk is estimated here from the fossil record and implications for our energy and economic future are explored. Over the last 534 million years (Myr), 50 extinction events present as peaks of genus loss‐and‐recovery cycles, each spanning ∼3–40 Myr. Atmospheric CO2 concentration oscillates with percent genus loss, leading in phase by ∼4 Myr and sharing harmonic periodicities at ∼10, 26 and 63 Myr. Over the last 210 Myr, where data resolution is highest, biodiversity loss is correlated with atmospheric CO2 concentration, but not with long‐term global temperature nor with marginal radiative forcing of temperature by atmospheric CO2. The end‐Cretaceous extinction of the dinosaurs is anomalous, occurring during a 20‐million year depression in atmospheric CO2 concentration and rising global temperature. Today's atmospheric CO2 concentration, ∼421 parts per million by volume (ppmv), corresponds in the most recent marine fossil record to a biodiversity loss of 6.39%, implying that contemporary anthropogenic CO2 emissions are killing ocean life now. The United Nations Intergovernmental Panel on Climate Change projects that unabated fossil fuel use could elevate atmospheric CO2 concentration to 800 ppmv by 2100, approaching the 870 ppmv mean concentration of the last 19 natural extinction events. Reversing this first global anthropogenic mass extinction requires reducing net anthropogenic CO2 emissions to zero, optimally by 2% per year starting immediately.