Science Study Finds Ancient Forests Thinned 35% During 56-Million-Year-Old Warming Event
Updated
Updated · Gizmodo · Aug 13
Science Study Finds Ancient Forests Thinned 35% During 56-Million-Year-Old Warming Event
3 articles · Updated · Gizmodo · Aug 13
Summary
A Science study reconstructed Wyoming’s Hanna Basin forest during the Paleocene-Eocene Thermal Maximum and found canopy density averaged 35% below pre-warming levels, with the steepest drop—about 61%—at the event’s onset.
Fossil leaf epidermal cells let Regan Dunn’s team estimate leaf area index, showing heat, drought and altered rainfall stressed trees enough to outweigh any growth boost from higher CO2.
The result undercuts the idea that more carbon simply greens the planet, because thinner forests store less carbon and can amplify warming through a feedback loop.
The warning is sharper for today: fossil-fuel carbon is entering the atmosphere about 10 times faster than during the PETM, while global greening has reversed across roughly 90% of vegetated land since around 2000.
Researchers say continued stress could cut carbon stored in forests’ aboveground biomass by up to 20% by 2100, though reforestation in places such as China shows some capacity for recovery.
If rising CO2 initially makes forests greener, how long before extreme heat and drought trigger a catastrophic global dieback?
Could the temporary greening of our planet be a deceptive warning sign of an impending collapse in global forest biomass?
Will modern forest management tactics be enough to save our woodlands when extreme warming turns them into massive carbon sources?
Forest Collapse in a Warming World: Lessons from the PETM and the Looming Threat to Global Carbon Sinks
Overview
This report reveals how, during the Paleocene-Eocene Thermal Maximum (PETM), massive carbon releases caused global temperatures to soar, first making ancient forests denser but then triggering a catastrophic collapse that wiped out 60% of their biomass. The collapse was driven by extreme heat and drought, which forced trees to close their pores, halting photosynthesis and leading to widespread death. Weakened forests became vulnerable to pests, wildfires, and further carbon release, crippling Earth’s natural carbon sinks for tens of thousands of years. Today, human-driven emissions are rising much faster than during the PETM, giving ecosystems even less time to adapt and increasing the risk of irreversible forest loss and climate feedbacks.