MASS EXTINCTIONS AND CLIMATE CHANGE: ANALOGS OF TODAY’S RAPID CLIMATE WARMING AND POTENTIAL BIOTIC CATASTROPHE

Anthropocene climate change is leading to an imminent biotic catastrophe that may be comparable to the five major mass extinctions in Earth’s history. We test this hypothesis based on faunal and environmental records of the Cretaceous-Paleogene boundary (KPB) mass extinction ~66.0 Ma and the Paleocene-Eocene Thermal Maximum (PETM) ~55.8 Ma, which are good analogs of today’s rapid climate change. The comparison is based on the rate and timing of climate warming and ocean acidification, which are the most detrimental consequences of increased atmospheric carbon dioxide (CO₂), and their impact on foraminifera, base of the marine food chain and key players in the biological carbon pump. During the KPB, Deccan volcanism in India led to abrupt hyperthermal warming and surface ocean acidification in the last ~25 ky of the Cretaceous that pushed ecosystems beyond tipping points resulting in the mass extinction. Two thirds of all planktic foraminifera species went extinct at the KPB and all but one survivor species went extinct in the first ~150 ky of the Paleogene disrupting the marine food chain and biological carbon pump. During the PETM, volcanism of the North Atlantic Igneous Province led to rapid warming (~10 ky) associated with abrupt methane degassing and shoaling of the carbonate compensation depth due to ocean acidification. These environmental perturbations led to temporary disappearance of planktic foraminifera in low latitudes and extinctions in benthic foraminifera followed by rapid recovery. Today, the rise in atmospheric CO₂ due to fossil fuels burning and associated increase in global temperatures are magnitudes faster than at the KPB or PETM due to volcanism. As a result, foraminifera already suffer increasing diversity loss, decreasing abundance, reduced calcification, dissolution and dwarfing, similar to foraminifera communities across the KPB and PETM. Today’s continued extreme rates of environmental change will likely exceed thresholds of adaptability and survivability within a few decades leading to the sixth mass extinction with a KPB-like response. In contrast, significantly reduced CO₂ input to the atmosphere may curtail the disastrous mass extinction effects leading to a PETM-like response with reduced extinctions and rapid recovery.