Claim: Global Warming Tipping Points Caused the Paleocene–Eocene Thermal Maximum

Guest essay by Eric Worrall

According to a study, The Paleocene-Eocene Thermal Maximum, an extreme spike of global warming which occurred 55 million years ago, was not just caused by volcanism and geological upheaval.

‘Tipping points’ in Earth’s system triggered rapid climate change 55 million years ago, research shows

by  University of Exeter

Scientists have uncovered a fascinating new insight into what caused one of the most rapid and dramatic instances of climate change in the history of the Earth.

A team of researchers, led by Dr. Sev Kender from the University of Exeter, have made a pivotal breakthrough in the cause behind the Paleocene-Eocene Thermal Maximum (PETM) – an extreme global warming event that lasted for around 150 thousand years which saw significant temperature rises. 

Although previous studies have suggested volcanic activity contributed to the vast CO₂emissions that drove the rapid climate change, the trigger for event is less clear.

In the new study, the researchers have identified elevated levels of mercury just before and at the outset of the PETM—which could be caused by expansive volcanic activity—in samples taken from sedimentary cores in the North Sea. 

Crucially, the research of the rock samples also showed that in the early stages of the PETM, there was a significant drop in mercury levels—suggested at least one other carbon reservoir released significant greenhouse gasses as the phenomenon took hold. 

The research indicates the existence of tipping points in the Earth’s System—which could trigger the release of additional carbon reservoirs that drove the Earth’s climate to unprecedented high temperatures.

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Read more: https://phys.org/news/2021-08-earth-triggered-rapid-climate-million.html

The abstract of the study;

Paleocene/Eocene carbon feedbacks triggered by volcanic activity

Sev Kender, Kara Bogus, Gunver K. Pedersen, Karen Dybkjær, Tamsin A. Mather, Erica Mariani, Andy Ridgwell, James B. Riding, Thomas Wagner, Stephen P. Hesselbo & Melanie J. Leng 

Abstract

The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO₂. However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of ‘tipping points’ in the Earth system, which can trigger release of additional carbon reservoirs and drive Earth’s climate into a hotter state.

Read more: https://www.nature.com/articles/s41467-021-25536-0

To be fair, unlike some studies, the authors of this study warn upfront in the main body of their paper that it is difficult to draw inferences from events which occurred during the Paleocene-Eocene Thermal Maximum which are relevant to modern times.