Long-term legacy of massive carbon input to the Earth system: Anthropocene versus Eocene

• Published in: Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences Vol. 371; no. 2001; p. 20120006
• Main Authors: Zeebe, Richard E., Zachos, James C.
• Format: Journal Article
• Language: English
• Published: England The Royal Society Publishing 28-10-2013
• Subjects: Anthropogenic Carbon; Climate; Eocene; Ocean Acidification; Palaeo; anthropogenic carbon; ocean acidification; palaeo; Eocene; climate
• ISSN: 1364-503X; 1471-2962
• DOI: 10.1098/rsta.2012.0006

Over the next few centuries, with unabated emissions of anthropogenic carbon dioxide (CO2), a total of 5000Pg C may enter the atmosphere, causing CO2 concentrations to rise to approximately 2000ppmv, global temperature to warm by more than 8C and surface ocean pH to decline by approximately 0.7 units. A carbon release of this magnitude is unprecedented during the past 56 million yearsand the outcome accordingly difficult to predict. In this regard, the geological record may provide foresight to how the Earth system will respond in the future. Here, we discuss the long-term legacy of massive carbon release into the Earth's surface reservoirs, comparing the Anthropocene with a past analogue, the PalaeoceneEocene Thermal Maximum (PETM, approx. 56Ma). We examine the natural processes and time scales of CO2 neutralization that determine the atmospheric lifetime of CO2 in response to carbon release. We compare the duration of carbon release during the Anthropocene versus PETM and the ensuing effects on ocean acidification and marine calcifying organisms. We also discuss the conundrum that the observed duration of the PETM appears to be much longer than predicted by models that use first-order assumptions. Finally, we comment on past and future mass extinctions and recovery times of biotic diversity.