Adding huge quantities of carbon dioxide into the atmosphere is set to cause the Earth's forests to wither and die rather than flourish, according to a new study that counters erroneous claims that fossil fuel pollution will green the planet. The research, published in a leading scientific journal, uses fossilized leaf cells from the Paleocene-Eocene Thermal Maximum (PETM) to reconstruct ancient forest responses to rapid carbon release.
Fossil Evidence Reveals Forest Collapse
The study focused on the PETM, a period about 56 million years ago when massive carbon emissions warmed the planet by up to 8°C (14°F). By analyzing fossilized leaf cells, researchers found that forests initially became dense but then collapsed dramatically, losing about 60% of their standing biomass.
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Lead author Regan Dunn from La Brea Tar Pits explained: "What we see is that as the carbon dioxide ramped up, the forests became very dense but then subsequently collapsed, opening up dramatically." This finding challenges the misconception that higher CO2 levels benefit plant life globally.
Implications for Modern Climate Change
The current rate of carbon emissions from burning fossil fuels is unprecedented, even compared to the PETM. The study's authors state this has "chilling implications" for today's forests, which are already suffering from dieback, wildfires, and deforestation.
"Forests are some of our best friends and allies but we are already seeing them die back, be cut down and consumed by wildfires," Dunn added. "It's happening quickly, every summer the change seems faster and faster."

Comparing PETM and Modern Carbon Emissions
| Factor | PETM (56 million years ago) | Modern Era |
|---|---|---|
| Carbon release duration | 130,000 years | ~250 years (industrial era) |
| Temperature increase | Up to 8°C | ~1.2°C so far, projected higher |
| Forest response | Dense then collapse (60% biomass loss) | Observed dieback and increased wildfires |
| Rate of carbon release | Rapid but slower than today | Fastest in known history |
Key Takeaways for Forest Conservation
- Carbon emissions harm forests, not green the planet, as fossil evidence shows.
- Forests may initially thrive with higher CO2 but then collapse under stress.
- Urgent action is needed to reduce emissions and protect existing forests.
- Wildfires and deforestation compound the negative effects of climate change.
Why This Study Matters
This research provides a stark warning about the future of Earth's forests. While plants need carbon to grow, excessive CO2 disrupts ecosystems, leading to biodiversity loss and reduced carbon storage capacity.
As policymakers and businesses consider climate strategies, this study underscores the need to prioritize emission reductions over geoengineering solutions that rely on CO2 fertilization.
FAQ
Do carbon emissions really harm forests?
What is the Paleocene-Eocene Thermal Maximum?
Can forests recover from carbon emissions?
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