Overview
- The paper led by paleobotanist Regan Dunn was published in Science on Thursday, Aug. 13, 2026, and is based on fossil material from Wyoming’s Hanna Basin.
- Researchers found canopy leaf area fell sharply at the Paleocene–Eocene Thermal Maximum, with a roughly 61% decline at the event’s onset and an average 35% thinner canopy that persisted for tens of thousands of years.
- The team reconstructed leaf area index by measuring the shape of epidermal cells in fossil leaf cuticles and calibrating that relationship with modern forest soils sampled across Central and South America.
- Canopy loss changed ecosystems and the landscape as tree death allowed ferns and warm‑climate plants to expand, ancient soils were replaced by coarser river deposits, and aboveground carbon storage dropped.
- The authors warn the PETM is a partial analog for today because humans are emitting CO2 about ten times faster and satellite and field data show greening has reversed in many regions since about 2000, which could trigger long-lived carbon‑cycle feedbacks unless emissions are rapidly cut.