Five million years of unyielding warmth this was the legacy of the “Great Dying,” a cataclysm so profound that it almost eliminated life from Earth. But for decades, the endurance of these super-greenhouse conditions past the volcanic onslaught of the Siberian Traps had been a mystery that nagged paleoclimatologists. And now, in a triumph of cross-border collaboration, an international team, armed with a rich Chinese fossil record and sophisticated climate-biogeochemical models, has shed light on the pivotal role played by tropical forests in this global crisis a lesson with unnerving relevance for today’s warming world.
The Permian–Triassic mass extinction, around 252 million years ago, was initiated by a rapid spurt of carbon dioxide associated with Siberian volcanism, raising global temperatures by as much as 10°C on land. But the first pulse of volcanism, though catastrophic, should have been succeeded by a slow return to planetary health since silicate weathering a mechanism whereby rain and plant roots dissolve rocks, sequestering atmospheric CO2 should have pulled the climate back from the edge. Yet Earth was stuck in a hothouse for millions of years, with equatorial surface temperatures greater than 34°C, much higher than ever before or since.
The missing link, scientists now contend, was the collapse of low-latitude rainforests. As Zhen Xu, lead author and University of Leeds research fellow, told CNN, The level of warming is far beyond any other event. The researchers’ reconstruction, derived from decades of fossil plant mapping in China, demonstrated that prior to the extinction, the tropics were filled with giant, intricate forests rainforests and peat bogs that served as planetary carbon sinks. But as the temperatures rose, these biomes were obliterated, and only small lycopods just centimeters high remained, with only hot, low-latitude refuges sheltering enclaves of larger vegetation.
Such a “coal gap” an interval during which coal-forming plants dropped from the geological record meant that the organic carbon cycle was broken. The death of the forests not only ceased carbon burial but also cut rates of silicate weathering in half, since the roots of plants and microorganisms are needed to decompose rocks and cause CO2 to be drawn down. As Benjamin Mills, co-author and professor of Earth system evolution at Leeds, told CNN, “Once the forests die, you’re changing the carbon cycle.” Michael Benton, paleontologist at the University of Bristol, added, “The absence of forests really impacts the regular oxygen-carbon cycles and suppresses carbon burial and so high levels of CO2 remain in the atmosphere over prolonged periods.”
To verify these hypotheses, the scientists coupled fossil-based biome reconstructions with the SCION Earth Evolution Model, a climate-biogeochemical model that includes the interactions of plant productivity, weathering, and carbon cycling. Their models indicated that the initial warming due to the volcanic eruptions was exaggerated and prolonged by the extinction of productive tropical vegetation, confining the planet into a high-temperature steady state for almost five million years. It was only when forests slowly recolonized the tropics that the organic carbon cycle and silicate weathering were restored, enabling Earth to slowly cool out of its hothouse trap.
Technical excellence of this research is in the reconstruction of global vegetation maps from both macrofossil and palynological evidence, painstakingly normalized for taphonomic biases and fragmentation of plant fossils. The Chinese fossil record, augmented by methodical excavations like the “vegetational Pompeii” of Inner Mongolia, yielded high-resolution photographs of Permian peat-forming forests, showing a multi-story complexity dominated by tree ferns, lycopsids, and mysterious Noeggerathiales (Permian vegetational Pompeii of Inner Mongolia). These reconstructions were cross-checked with geochemical proxies, including carbon and strontium isotopes, and compared to climate-vegetation model outputs, which pinpointed tipping points and hysteresis in the climate system.
The message for the world today is stark. Today’s tropical rainforests, like the Amazon, are threatened by compounding danger from warming, drought, and deforestation. Recent studies warn that up to half of the Amazon could reach a tipping point by 2050, with degraded forests becoming net carbon sources and triggering feedbacks that further destabilize the climate (Critical transitions in the Amazon forest system) (Amazon rainforest could reach ‘tipping point’ by 2050, scientists warn). As Mills cautioned, “There is a tipping point there. If you warm tropical forests too much, then we have a very good record of what happens. And it’s extremely bad.”
The history of the Great Dying therefore becomes more than just an ancient catastrophe tale it is a scientific warning inscribed in stone and coal, a clue that the climate resilience of our planet depends on the destiny of its forests, both ancient and modern.
