Researchers examining fossilized leaf cells from the Paleocene-Eocene Thermal Maximum, a period approximately 56 million years ago when atmospheric carbon was released rapidly over 130,000 years, have determined that the resulting climate change caused significant forest decline rather than growth. The analysis, published in Science, reveals that while initial increases in carbon dioxide temporarily boosted plant density, the forests subsequently experienced dramatic collapse as temperatures rose by approximately 8 degrees Celsius. Lead researcher Regan Dunn from the La Brea Tar Pits and Natural History Museum of Los Angeles County noted that roughly 60 percent of standing vegetation biomass disappeared during this period.
The findings directly address arguments from some policymakers who contend that elevated carbon dioxide levels benefit plant life and should not be considered harmful. Officials in the current administration have publicly stated that increased CO2 supports plant growth and questioned whether carbon dioxide constitutes a pollutant. However, the research demonstrates that while carbon provides essential building material for plants, additional factors including extreme heat, water stress, and nutrient depletion ultimately overwhelm any initial benefits from increased atmospheric carbon.
According to the study, the transition from expanding to contracting forests occurred around 2000, when the cumulative effects of drought and heat stress began outweighing the advantages of elevated CO2. Current observations support this finding, with documented tree mortality increasing across Europe, North America, and the Amazon. Researchers determined ancient forest density by analyzing fossilized leaf cuticle fragments, enabling them to track forest canopy changes across multiple millennia.
Experts emphasize that current carbon emissions are occurring at rates unprecedented in both historical and geological records. While the ancient carbon release unfolded over thousands of years through volcanic activity, contemporary emissions are happening over decades through deliberate fossil fuel combustion. Scientists warn that the accelerated pace leaves ecosystems insufficient time to adapt and that humanity must significantly reduce carbon emissions to avoid repeating the forest collapse observed in the distant past.
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