Wyoming fossils reveal ancient forests that collapsed during extreme global warming and took more than 100,000 years to recover: a stark warning for today’s climate.
Fossils from Wyoming reveal how forests responded when Earth experienced one of its most intense episodes Global warming About 56 million years ago. A new study, published in the journal Science on August 13, 2026, reconstructed the structure of forests during the Paleocene and Eocene Thermal Maximum, or PETM, and found that their canopies became dramatically more open as temperatures rose and moisture availability decreased. Researchers estimate that forest canopy cover declined by about 60% and remained significantly low for more than 100,000 years before recovering. This finding provides a striking example of how climate-induced stress can alter entire ecosystems for unusually long periods. Scientists warn that the PETM is not an accurate preview of modern climate change, but its fossil record provides an important warning about what could happen when warming pushes vegetation beyond its ecological limits.
Wyoming fossils Reveal what happened to Ancient forests During global warming
The new research is titled “Forest canopy decline under rising carbon dioxide during the Paleocene and Eocene thermal maximum” and was published in the journal Science by Regan E. Dunn and colleagues. The team examined fossil material from Wyoming to reconstruct not only the plants that lived there but also the physical structure of the forest above them. The PETM began about 56 million years ago after the injection of large amounts of carbon into the atmosphere and oceans, resulting in a global warming estimated at 5 to 6 degrees Celsius, with some reconstructions putting the increase at up to 8 degrees Celsius. Warming has changed vegetation in many areas, and Wyoming provides an unusually detailed land record because sediments from that period preserve foliage, pollen, and other plant remains. Previous work in the Bighorn Basin has shown that the region’s forests experienced significant change during the event. Ellen Currano, a paleontologist at the University of Wyoming who has studied these forests for years, previously described the change as “almost a complete turnover of plants.”
Fossil leaves revealed the density of the ancient canopy
The researchers developed the reconstruction using microscopic details preserved in the fossilized leaf epidermis, the thin waxy layer that covers leaves. The shape of epidermal cells changes depending on how much sunlight reaches the developing leaf. Leaves growing under heavy shade tend to develop more elongated cells, while those exposed to strong sunlight develop shorter, more rounded cells. By calibrating this relationship to modern forests, scientists can use fossil epidermis to estimate the leaf area index, or LAI, which measures the amount of foliage relative to the area of land beneath it. A higher LAI value indicates a denser, more layered canopy, while a lower value indicates a more open forest. The research therefore provides a way to reconstruct an aspect of a 56-million-year-old forest that cannot be observed directly. Previous work by the team has already proven this method in Wyoming, while the new scientific study applies it to show how canopy structure shifted during the PETM. Previous work by Regan Dunne and his collaborators established fossil leaf cuticles as a proxy for reconstructing the leaf area index, allowing researchers to estimate the density of ancient forest canopies from the properties of microscopic leaf cells.
Heat and drought have pushed the forest beyond its limits
The forest did not enter the PETM period in a weakened state. According to the study, canopy density was exceptionally high before rapid warming began. As temperatures rose, the conditions that supported the dense vegetation deteriorated. Heat and reduced water availability increased stress on the trees, and the canopy opened as the trees died. This decline had significance beyond the plants themselves, because a dense canopy affects sunlight, ground temperature, humidity, photosynthesis, and the movement of water through the ecosystem. As the forest became more open, the surrounding landscape also changed, with geological evidence indicating a shift towards coarser river deposits and changing sediment movement. The results demonstrate how climate stress can spread across an ecosystem rather than affecting individual species in isolation. A separate modeling study published in Nature Communications concluded that PETM-scale warming could have exceeded the adaptive capacity of vegetation systems, leading to long-term declines in ecosystem productivity and carbon regulatory functions.
The forests eventually returned, but recovery took more than 100,000 years
The story of the ancient forest was not one of permanent devastation. Once the extreme climate of the PETM period began to subside, temperatures gradually decreased and water availability improved. The forests eventually recovered, and vegetation may later become denser than before the warming event. But the timeline is what makes this discovery amazing. The new research suggests that the canopy has remained significantly variable for more than 100,000 years, meaning that an ecosystem that existed in a relatively stable form may take thousands of generations to regain its previous structure. This long recovery is consistent with other research showing a lag of 70,000 to 100,000 years in the recovery of biospheric carbon stocks after PETM warming. The record therefore demonstrates the resilience and fragility of forests. It is possible for them to return after major environmental disturbance, but recovery on geological timescales offers little comfort for human communities that depend on forests today.
The Wyoming record offers a warning about today’s climate
The PETM period is one of the most useful in-depth comparisons for understanding global warming, but scientists stress that it is not a direct prediction of the future. One major difference is the speed of carbon release. Research highlighted by the Smithsonian suggests that the initial carbon release associated with the PETM period occurred much more slowly than current human-driven emissions, with estimates suggesting the ancient rate was roughly one-tenth the modern rate. This difference is important because ecosystems have a greater opportunity to migrate, adapt, or adapt when environmental change occurs slowly. Today, forests simultaneously face rising temperatures, drought, wildfires, pests, habitat fragmentation, and land use pressures. So the new study does not show that modern forests would necessarily take 100,000 years to recover. Instead, it shows that rapid or sustained warming can profoundly alter forest structure and that ecosystem recovery can extend beyond a human lifetime. The reconstruction by Regan Dunn and her colleagues provides a geological record of these vulnerabilities, while the forest’s eventual return also shows that resilience is possible when climate pressures eventually ease.
