The Permian-Triassic mass extinction was caused by volcanic eruptions in what is now the Siberian Traps, releasing 100,000 billion metric tons of carbon dioxide into the atmosphere over a million years and killing off most animals, except for a few lineages — including the animals that would evolve, in the Late Triassic, into the earliest dinosaurs. Recovery took several million years. Now scientists have used modelling and plant fossils to follow the biosphere’s transition to 10 degrees of warming which eradicated tundra habitats and made polar regions temperate, helping us understand the consequences of this extreme climate change in deep time — and possibly even the consequences of our own CO₂ emissions.

The mass extinction that ended the Permian geological epoch, 252 million years ago, wiped out most animals living on Earth. Huge volcanoes erupted, releasing 100,000 billion metric tons of carbon dioxide into the atmosphere. This destabilized the climate and the carbon cycle, leading to dramatic global warming, deoxygenated oceans, and mass extinction. However, many plants survived, leaving behind fossils which scientists have used to model a dramatic 10 degree rise in global temperatures.

“While fossilized spores and pollen of plants from the Early Triassic do not provide strong evidence for a sudden and catastrophic biodiversity loss, both marine and terrestrial animals experienced the most severe mass extinction in Earth’s history,” explained Dr Maura Brunetti of the University of Geneva, lead author of the article in Frontiers in Earth Sciences. “Life on Earth had to adjust to repeated changes in climate and the carbon cycle for several million years after the Permian-Triassic Boundary.

“Our study links land plant macrofossil assemblages and numerical simulations describing possible climates from the late Permian to the early Triassic. We show that a shift from a cold climatic state to one with a mean surface air temperature approximately 10⁰C higher is consistent with changes in plant biomes.”

Climate crisis

The scientists studied five stages on either side of the Permian-Triassic Boundary: the Permian Wuchiapingian and Changhsingian, the early Triassic Induan and Olenekian, and the middle Triassic Anisian. They combined a map of Earth’s geography at that time with plant fossil data, assigning plant genera to six major biomes to estimate what the local climate looked like in different places based on the plants found there. Changes over time in the fossil record served as observational data to test the scientists’ climate models.

These biomes ranged from hot, humid ‘tropical everwet’ biomes, to seasonal tropical or temperate biomes and desert biomes. Different temperatures and CO₂ levels favor different biomes. In cold temperature states, tropical latitudes feature desert, while at higher latitudes cold-temperate vegetation and tundra appear. Hot states feature temperate vegetation at polar latitudes and desert at equatorial latitudes. The more CO₂ is present, the warmer and wetter biomes are.

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The seeds of recovery

The scientists then used statistical analysis to estimate the similarity between the existing plant fossil records and simulations of the biomes that would have flourished in different temperature states and CO₂ levels. They found that these biomes changed dramatically at the Permian-Triassic Boundary, as the planet moved from a cold climate to a warm one.

The earliest periods, in the Permian, were cold, while the first period of the Triassic — the Induan — had a disturbed climate which the scientists couldn’t identify. This could be caused by sampling biases or poorer fossil preservation, or it could be due to short-term climate oscillations which didn’t allow biomes to stabilize. We need more fossil data to clarify this.

The later Triassic, however, was much hotter. The following periods — the Olenekian and Anisian — stabilized at temperatures 10 degrees higher than previously.

Heating up

“This transition from the colder climatic state to the hotter state is marked by an increase of approximately 10⁰C in the mean global surface air temperature and an intensification of the water cycle,” said Brunetti. “Tropical everwet and summerwet biomes emerged in the tropics, replacing predominantly desertic landscapes. Meanwhile, the warm-cool temperate biome shifted towards polar regions, leading to the complete disappearance of tundra ecosystems.”

“The shift in vegetation cover can be linked to tipping mechanisms between climatic steady states, providing a potential framework for understanding the transition between Permian and Triassic,” added Brunetti. “This framework can be used to understand tipping behavior in the climate system in response to the present-day CO₂ increase. If this increase continues at the same rate, we will reach the level of emissions that caused the Permian-Triassic mass extinction in around 2,700 years — a much faster timescale than the Permian-Triassic Boundary emissions.”

However, as with the climate of the Induan period, more data and more refined models are needed for clearer results.

“The comparison between simulated biomes and the dataset is influenced by uncertainties, arising from paleogeographic reconstructions and the classification of fossil assemblages into biomes,” cautioned Brunetti. “Furthermore, our climate modeling setup relies on offline coupling between models — the vegetation model uses the final outputs of the climatic model for biome reconstruction. This could be enhanced using a dynamic vegetation model.”

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