How Ancient Mass Extinctions Revealed Earth’s Evolution into a Super Greenhouse

Following a dramatic increase in carbon dioxide levels 252 million years ago, the death of forests resulted in enduring climate alterations, with the greenhouse effect persisting for millions of years.

Researchers striving to comprehend this phenomenon, which triggered the largest mass extinction in Earth’s history, caution that ongoing greenhouse gas emissions may lead to similar outcomes.

The extinction events of the Permian and Triassic are believed to have been triggered by extensive volcanic activity in what is now Siberia, elevating atmospheric CO2 concentrations.

The planet’s surface temperature soared by as much as 10°C, with average temperatures in the equatorial regions climbing to 34°C (93°F)—a rise of 8°C above the current average.

These extreme conditions persisted for roughly 5 million years, causing over 80% of marine species and upwards of 70% of terrestrial vertebrate families to become extinct, according to some estimates.

Although some scientists have recently posited that these mass extinction events may have limited effects on terrestrial ecosystems, Andrew Meldis from the University of Adelaide expresses confidence that life was nearly extinguished 252 million years ago.

“Small pockets of life might survive mass extinctions in isolated enclaves, but many areas within the Permian-Triassic fossil record reveal a complete ecosystem collapse,” notes Meldis.

He and his team scrutinized the fossil record to investigate why the Super Greenhouse event, which drives mass extinction, lasted five million years—far longer than the 100,000 years predicted by climate models.

The findings revealed that vast expanses of forests, originally with canopies of around 50 meters, were supplanted by resilient underground flora, typically ranging from 5 cm to 2 meters in height. Additionally, peat marshes, significant carbon storage ecosystems, vanished from tropical areas.

Employing computer models of Earth’s climatic and geochemical systems, researchers indicated that the depletion of these ecosystems contributes to elevated CO2 levels persisting for millions of years. This predominantly occurs because vegetation plays a crucial role in weathering, the mechanism that extracts carbon from the atmosphere and sequesters it in rocks and soil over extensive timescales.

With atmospheric CO2 levels rising rapidly, the parallels to the present are striking, asserts Meldis. As temperatures escalate, tropical and subtropical forests may find it increasingly challenging to adapt, potentially surpassing thresholds where vegetation ceases to maintain climate equilibrium.

Meldis explains that simply restoring former ecosystems will not lead to a “ping-pong effect.” He emphasizes that the atmosphere cannot be swiftly rejuvenated after the loss of the equatorial forest.

“You’re not transitioning from an ice house to a greenhouse and then back; the Earth will find a new equilibrium, which may differ significantly from prior states,” he elaborates.

Catlin Maisner, a researcher at the University of New South Wales—who was not involved in the study—describes reconstructing these events as analogous to “trying to assemble a jigsaw puzzle with many missing pieces,” yet acknowledges the team’s arguments as “plausible.”

However, she notes considerable uncertainty regarding oceanic processes during this period. “The ocean harbors far more carbon than land and atmosphere combined, and we still lack a comprehensive understanding of how marine biology, chemistry, and physical circulation were affected during that event,” cautions Meissner.