252 Million Years Ago, Earth’s Climate Hit Reset

What fossil plants can teach us about global tipping points, and what that means for our future

Have you ever seen a fossilized fossil fern?

They are thin, fragile, and pressed into rock like a fingerprint from a world that no longer exists. Some of the most iconic I’ve seen come from the Triassic, just after the most catastrophic mass extinction Earth has ever seen (yes, worse and earlier than the one that wiped out the dinosaurs).

These impressions remind us of something crucial for the history of our planet: life doesn’t just end during extinction events; it reshuffles, regrows, and reclaims.

Morphological features of *Coniopteris simplex (fossil fern)*: A–B) Sterile pinnae with thick and thin fronds; C) Hemidimorphic pinna with sterile and fertile parts; D) Fertile pinna with sorus; E) Sori with stalks; F–G) Close-ups of sporangia showing annulus and in situ tetrad spores — Li et al., 2024

As a paleontologist, I’ve spent most of my career piecing together who lived where, when, and most importantly, why. So when I saw a new study linking ancient plant fossils to climate models that simulate the aftermath of the Great Dying (also known as the Permian–Triassic extinction event), I knew this was the perfect piece for those interested in both climate change and paleontology.

This wasn’t just another tale of extinction. It was a window into how Earth’s climate system can flip, suddenly and violently, and how living things try to pick up the pieces.

Around 252 million years ago, the Permian-Triassic extinction wiped out over 80% of marine species and most land animals. But while the spotlight often falls on the dinosaurs’ earlier cousins or the deep-sea die-offs, this paper shifts our focus to plants and the climate system that shaped their fate.

The study asked a deceptively simple question: how did Earth’s vegetation change across the Permian-Triassic boundary, and what does that tell us about the planet’s climate at the time?

Permian–Triassic paleogeography **(A)** and corresponding bifurcation diagram **(B)** in terms of the equilibrium values of the global mean surface air temperature vs. the atmospheric CO2CO2 content (Ragon et al., 2024). Yellow triangles, red circles, and blue squares represent averages over 100 years for a given forcing value for the hot, warm, and cold attractors, respectively. Black arrows identify the location of coupling simulations between MITgcm and the vegetation model BIOME 4. The vertical dashed line corresponds to 320 ppm, the forcing value at which coupling is performed in the three attractors — Ragon et al., 2025

To answer it, they combined plant macrofossil records (things like leaves, seeds, and stems) with advanced climate simulations. These models, powered by decades of geological and atmospheric data, recreated what Earth’s surface may have looked like before, during, and after the extinction event.

The surprise? Their models revealed that Earth didn’t have one stable climate at the time, it had three possible steady states: cold, warm, and hot.

Which of these states the planet settled into depended on how much CO₂ was in the atmosphere and how fast it increased.

The method was surprisingly elegant. The team used well-dated plant fossils from five distinct stages spanning the extinction: Wuchiapingian and Changhsingian (late Permian), Induan and Olenekian (early Triassic), and Anisian (middle Triassic). Each plant genus was tied to a specific kind of biome: tropical everwet, seasonal summerwet, temperate, desert, and so on.

By comparing these real-world fossil assemblages to vegetation patterns predicted by their models, the researchers could “match” past biomes to simulated ones. It’s a bit like cross-referencing a witness sketch of a forest with Google Earth snapshots from different time periods.

Comparison of plant fossil assemblages of Wuchiapingian age (259.51–254.14 Ma) superposed with major biomes modeled at 320 ppm for the **(A)** hot state and **(B)** cold state — Ragon et al., 2025

Statistical tests helped them figure out which modeled climate state best fit the fossil data at each time point. And the results showed a world flipping through extremes.

During the late Permian, Earth’s climate was relatively cool. Polar regions supported tundra, temperate belts wrapped around mid-latitudes, and deserts appeared near the tropics. The fossil plant communities matched this picture closely.

But everything changed as CO₂ levels skyrocketed, fueled by massive volcanic eruptions in Siberia that poured carbon into the atmosphere for nearly a million years.

In the wake of this, the Induan period appears shady. Fossil evidence suggests a chaotic climate with frequent oscillations, too unstable for ecosystems to settle. Think of it like a planet reeling from shock, its ecosystems disoriented and gasping for equilibrium.

By the time the Triassic reached the Olenekian and Anisian stages, however, a new normal had emerged: the hot state. The tundra disappeared. Deserts shrank. Humid tropical forests crept further from the equator, and temperate vegetation reached the poles. Yes, the poles.

Distribution of the major biomes (see Table 1) for **(A–C)** hot, **(D, E)** warm, and **(F–H)** cold states, with the atmospheric CO2CO2 content varying, as indicated next to the labels. The white area corresponds to ocean — Ragon et al., 2025

In numerical terms, Earth had warmed by 10°C. That’s not a typo. Ten degrees is the difference between an ice age and a greenhouse world.

What makes this study especially compelling isn’t just the match between fossil and model, it’s what that match implies.

“This transition… is marked by an increase of approximately 10°C in the mean global surface air temperature and an intensification of the water cycle,” Dr. Brunetti explains. Polar regions turned green. Deserts made way for jungles. Biomes didn’t just shift; they jumped into new zones entirely.

And those jumps weren’t random. The study suggests that Earth’s climate system, like a ball in a landscape of valleys, can settle into different stable “attractors.” But add enough CO₂, and you can tip the ball into a new valley. Once it’s there, getting it back is hard.

That’s where the modern connection comes in.

If we keep emitting CO₂ at our current pace, the authors estimate we’ll hit the levels that triggered the Great Dying in about 2,700 years. That may sound distant, but in geological terms, it’s tomorrow. And unlike the slow-building volcanoes of the Permian (over a million years), our emissions are happening at lightning speed.

Summary of the comparison between the vegetation distribution associated with macrofossil records from the late Permian to the Early Triassic (Nowak et al., 2020) and the simulated climatic attractors, obtained using an offline coupling between the MITgcm and BIOME4 models, as described by Ragon et al. (2024) — Ragon et al., 2025

From a paleontologist’s perspective, I find it humbling. We often imagine past extinctions as alien catastrophes, unfolding in worlds unrecognizable from our own. But the forces at play then are disturbingly familiar: carbon, temperature, tipping points.

And while the plants of the Triassic eventually bounced back, it took millions of years and a complete reorganization of life. There’s no guarantee that today’s forests, wetlands, or coral reefs would make it through a similar upheaval. Or that we’ll be here to see it.

But there is a silver lining. Studies like this remind us that ecosystems leave clues, sometimes buried in rock for hundreds of millions of years. And if we’re willing to read them, we might find not just warnings, but wisdom.

Because in the end, it’s not just about what happened back then. It’s about what happens next.

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Best,
Sílvia P-M, PhD Climate Ages