What caused an extreme global warming event that lasted for around 150 thousand years?

Tipping points in Earth’s system triggered rapid climate change 55 million years ago.


Past studies have suggested that the rise in CO2 emissions from volcanic activity triggered rapid climate change. However, the trigger for the event is less clear.

Paleocene-Eocene Thermal Maximum (PETM), also called Initial Eocene Thermal Maximum (IETM), is an extreme global warming event that lasted for around 150 thousand years. What triggered the PETM remains unclear.

A new study uncovered a fascinating new insight into what caused the most rapid and dramatic instances of climate change in the history of the Earth. The study suggests that the tipping points in Earth’s system triggered rapid climate change 55 million years ago.

Scientists identified elevated levels of mercury just before and at the outset of the PETM. This detection was made in samples taken from sedimentary cores in the North Sea.

Analysis of rock samples reveals a significant drop in mercury levels during the early stages of the PETM; there was a significant drop in mercury levels. It means, 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.

Dr. Kender, a co-author on the Camborne School of Mines study, based at the University of Exeter’s Penryn Campus in Cornwall, said: Greenhouse gasses such CO2 methane were released to the atmosphere at the start of the PETM in just a few thousand years.

“We wanted to test the hypothesis that large volcanic eruptions triggered this unprecedented greenhouse gas release. As volcanoes also release large quantities of mercury, we measured the mercury and carbon in the sediment cores to detect any ancient volcanism.”

“The surprise was that we didn’t find a simple relationship of increased volcanism during the greenhouse gas release. We found volcanism occurred only at the beginning phase, and so another source of greenhouse gasses must have been released after the volcanism.”

Analysis of new sedimentary cores from the North Sea shows the presence of high levels of mercury. These samples showed numerous peaks in mercury levels before and at the outset of the PETM period—suggesting it was triggered by volcanic activity.

Dr. Kender added: “We were able to carry out this research as we have been working on exceptionally well preserved new core material with collaborators from the Geological Survey of Denmark and Greenland. The excellent preservation allowed precise detection of both the carbon released to the atmosphere and the mercury. As the North Sea is close to the region of volcanism thought to have triggered the PETM, these cores were ideal for detecting the signals.”

“The volcanism that caused the warming was probably vast deep intruded sills producing thousands of hydrothermal vents on a scale far beyond anything seen today. Possible secondary sources of greenhouse gasses were melting permafrost and seafloor methane hydrates due to the initial volcanic warming.”

Journal Reference:

  1. Sev Kender et al., Paleocene/Eocene carbon feedbacks triggered by volcanic activity, Nature Communications (2021). DOI: 10.1038/s41467-021-25536-0


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