Ancient world global warming event hints at our future

A study of the ancient world has revealed something remarkable about the possible future of our planet.

About 56 million years ago, a large release of greenhouse gases, likely spurred by volcanic activity, caused a period of sudden global warming known as the Paleocene-Eocene Thermal Maximum (PETM). The latest findings, published in the journal Scientists progressreveal that there was an additional transient increase in atmospheric CO2 just prior to the PETM, which resulted in a brief period of ocean acidification and warming.

Importantly, the amount of carbon released into the atmosphere during this precursor event was roughly equal to current cumulative carbon emissions from fossil fuel burning and other human activities.
Get more updates on this story and more with The planour daily newsletter: Register for free here.

Discover the secrets of marine sediments

“The PETM is an important geological climate event because it provides one of the best comparisons to current climate change and can help inform us about how the Earth system will respond to current and future warming,” the author explained. Principal Tali Babila, Postdoctoral Research Associate currently at University of Southampton.

The new finds based on a survey marine sediments deposited in shallow waters along the Atlantic coast of the United States. Because sea levels were higher during the PETM and parts of Maryland, Delaware, and New Jersey were underwater at the time, the researchers chose sediment cores drilled there to the study.

PETM is identified in marine sediments by a dramatic change in carbon isotopic composition and other indicators of severe changes in ocean chemistry caused by the uptake of large amounts of CO2. Additionally, marine sediments contain the small shells of tiny marine organisms called foraminifera that lived in the surface waters of the ocean, and the chemical makeup of these shells documents the environmental conditions under which they formed.

Researchers were able to reconstruct an accurate record of ocean acidification by analyzing the boron isotopic composition of individual foraminifera using new analytical methods developed at the University of Southampton in the UK. This was part of a suite of geochemical analyzes used to recreate environmental changes during the PETM precursor and main event.

Preceded by a brief warming period

The researchers concluded that the precursor signal in parts of Maryland involved a global event that likely lasted a few decades or even millennia. The two carbon pulses resulted in dramatically different mechanisms and time scales for the Earth’s carbon cycle and climate system recovery, with carbon emissions during the PETM exceeding the ocean’s buffering capacity. It took tens of thousands of years for Earth’s climate system to recover from the most extreme PETM.

These two events offer unique insight into how Earth’s current climate could react if the use of fossil fuels is not stopped and carbon emissions continue to increase at their current rate. The short-lived precursor event shows what could happen if current emissions are rapidly reduced, while the far more intense global warming of the PETM describes the effects of continued carbon emissions into the atmosphere at the current rate.

“While natural geological processes such as rock weathering and carbon burial eventually allowed Earth to recover from PETM, it took hundreds of thousands of years,” Babila said. “So this is further evidence that urgent action is needed today to rapidly reduce the amount of carbon released into the atmosphere to avoid lasting effects.”

Summary of the study:

The Paleocene-Eocene Thermal Maximum (PETM) is recognized by a major negative isotope of carbon (δ13C) excursion (CIE) meaning an injection of isotopically light carbon into exogenous reservoirs, the mass, source and timing of which continue to be debated. Evidence for one or more transient precursor carbon releases has been identified in a few localities, although it remains equivocal whether there is a global signal. Here we present the foraminifera δ13C records from a section of marine continental margin, which reveal a negative pre-appearance excursion (POE) of 1.0–1.5‰, and a concomitant increase in sea surface temperature of at least 2 °C and a drop in ocean pH. The recovery of the two δ13The C and pH before the onset of the CIE and the apparent absence of a POE in the deep-sea records suggest a rapid release of carbon (

Teresa H. Sadler