The numbers come first: 60% canopy loss, more than 100,000 years of recovery time, and a rate of carbon release today that is roughly 10 times faster than the natural processes that drove the Paleocene-Eocene Thermal Maximum, or PETM. Those are the central findings of a new study published in the journal Science, led by paleobotanist Regan E. Dunn and colleagues.
What the fossils show
Fifty-six million years ago, global temperatures rose by as much as 11 degrees Fahrenheit (6 degrees Celsius) during the PETM, one of Earth's most intense episodes of greenhouse warming. In what is now southern Wyoming, forests that once supported relatives of elms, walnuts, dawn redwood and avocado trees gave way first to ferns, then to palms and other warmth-loving plants spreading northward.
The research team reconstructed those ancient forests not from whole specimens but from microscopic plant cuticles — the thin, waxy outer skin of leaves that can survive for millions of years in organic-rich sediments. The shape of epidermal cells preserved in those fragments reflects how much sunlight the leaf received while growing: elongated cells indicate shade from a dense canopy; shorter, rounder cells indicate more open conditions.
By calibrating that cell-shape relationship against soils collected from forests across Central and South America with known canopy densities, the researchers built a tool to measure what ecologists call the leaf area index — a standard gauge of forest density — for forests that vanished tens of millions of years ago.
The timeline of collapse
One finding stood out: the Wyoming forests did not enter the PETM already weakened. Just before rapid warming began, canopy density reached its greatest level in hundreds of thousands of years, likely because rising atmospheric carbon dioxide initially stimulated plant growth. A leading theory attributes that early carbon dioxide increase to volcanic eruptions.
The recovery did not follow. As temperatures climbed, heat and drought overwhelmed the growth benefits of higher carbon dioxide. The canopy thinned rapidly, ancient soils gave way to coarser river deposits, and the diminished forest altered how water and sediment moved through the basin. That reduced state persisted for well over 100,000 years.
The researchers describe the PETM as Earth's closest natural analog to current warming conditions, with one critical difference: humans are releasing carbon dioxide roughly 10 times faster than the planet's natural processes did during that event.
The bottom line
The science here is straightforward, and the data deserve a clear-eyed reading rather than a political one. Forests are not merely scenery — their canopy structure controls carbon storage, water cycles and soil stability. A 60% canopy loss that required more than a century of millennia to reverse is a material fact about ecosystem resilience, whatever one's view of climate policy.
For free-market readers, the relevant question is not whether to panic but where the productive response lies: in innovation, in property-rights frameworks that give landowners incentives to manage forests well, and in energy policy that weighs real tradeoffs rather than mandating outcomes from the top down. The fossil record is data. What governments do with it is a choice — and that choice carries a price tag the taxpayer will ultimately settle.
