Fossils show huge carbon emissions harm forests, not ‘green the planet’

For years, political figures and climate skeptics have insisted that surging carbon dioxide emissions act as a blanket benefit for the natural world, arguing that because plants consume CO2 to grow, industrial pollution essentially greens the planet. Figures such as Interior Secretary Doug Burgum and Energy Secretary Chris Wright have asserted that carbon dioxide is not a pollutant and that a warmer, gas-rich world helps vegetation thrive. But a landmark study published in the journal Science offers a stark historical correction, showing that runaway carbon emissions ultimately cause forests to wither rather than flourish.

Led by paleobotanist Regan Dunn of the Natural History Museum of Los Angeles County and the La Brea Tar Pits, an international team of researchers reconstructed forest canopies from 56 million years ago. They focused on the Paleocene-Eocene Thermal Maximum, an abrupt global warming event triggered by massive volcanic activity that released greenhouse gases on an unprecedented scale. During this ancient period, global temperatures rose by as much as 8 degrees Celsius, or 14 degrees Fahrenheit, over roughly 130,000 years. By studying this episode, scientists sought to understand how terrestrial ecosystems respond to extreme carbon injections.

To measure prehistoric forest density without relying on subjective terms like woodland or open canopy, the research team pioneered an objective quantitative technique. They analyzed fossilized leaf cuticle fragments, specifically examining the epidermal cells preserved in organic-rich coal layers within Wyoming’s Hanna Basin. These microscopic cells, which resemble interlocking puzzle pieces, vary in shape depending on the amount of light the developing leaf received. By establishing a correlation between modern leaf cells and leaf area index—a standard measure of canopy density—the team could accurately estimate how much foliage shaded the ancient landscape.

The findings overturned conventional assumptions about plant growth under elevated carbon conditions. While higher CO2 levels theoretically boost photosynthesis, the researchers discovered that the devastating consequences of rapid warming rapidly overwhelmed any physiological benefits. As temperatures soared and precipitation patterns shifted, severe droughts gripped the landscape, plunging the forest canopy into crisis. At the onset of the thermal maximum, leaf area index plummeted by roughly 61%, and overall canopy cover across the period thinned by an average of 35% as vegetation died back and species migrated northward.

This prehistoric collapse carries profound implications for modern ecosystems, where human activity is pumping carbon into the atmosphere at a rate ten times faster than the natural ancient event.