In news that will surprise exactly no one who has ever seen a wildfire, a new study has confirmed that dumping vast quantities of carbon dioxide into the atmosphere is not, in fact, going to turn Earth into a lush paradise. Instead, it'll likely make our forests wither and die. Who knew?

Researchers analyzed fossilized leaf cells from the Paleocene-Eocene Thermal Maximum (PETM), a prehistoric period about 56 million years ago when carbon was released over 130,000 years, heating the planet by up to 8C (14F). The findings, published in Science, show that forests initially got denser as CO2 rose, but then spectacularly collapsed, with about 60% of the standing vegetation biomass disappearing.

"As the carbon dioxide ramped up, the forests became very dense but then subsequently collapsed," said Regan Dunn of La Brea Tar Pits and the Natural History Museum of Los Angeles County. "This should be a concern because the rate of carbon release has never been higher than now."

This directly contradicts the cheerful claims from certain Trump administration figures, like Interior Secretary Doug Burgum, who told Fox Business that "CO2 was never a pollutant" and that plants "thrive with more CO2." Energy Secretary Chris Wright has similarly claimed that a "warmer planet with more CO2 is better for growing plants." The new paper begs to differ, noting that trees need more than just CO2 - they also need, you know, not to be incinerated by heat stress, pests, and wildfires.

The study found that around 2000, the greening effect of extra CO2 was overtaken by the browning effects of drought and heat. Since then, tree mortality has escalated globally, with trees in the tropics literally dying of thirst. Dunn noted that "quite a lot of tree mortality" is now occurring in Europe, North America, and the Amazon.

The PETM changes took thousands of years, driven by volcanic activity. Our current carbon release is happening over decades, giving ecosystems far less time to adapt. As Trevor Keenan of UC Berkeley put it, "The headline is that warming won." And unlike ancient forests, today's forests also face logging, fragmentation, and altered fire regimes. So if forests thinned under the slower, cleaner version of this experiment, that's not a reassuring precedent.

Dunn's advice? "Keep fossil fuels in the ground." Because once we cross those thresholds, recovery takes a time span that, on human timescales, is basically forever.