Imagine a world where plants, the silent heroes of our planet's climate, suddenly falter under the heat—could this ancient disaster foreshadow our own future? That's the startling lesson from an event 56 million years ago, when Earth's temperature spiked dramatically, and vegetation struggled to keep up.
About 56 million years back, our planet underwent an abrupt and intense warming phase. Over roughly 5,000 years, atmospheric carbon levels surged dramatically, causing global temperatures to climb by around 6°C—a change that reshaped ecosystems in ways we're only now beginning to fully grasp (see the study at https://doi.org/10.1073/pnas.2318779121).
In our latest research, published in Nature Communications (https://doi.org/10.1038/s41467-025-66390-8), we reveal a fascinating twist: many plants couldn't adapt fast enough to this heatwave, leading them to absorb less carbon from the air. This, in turn, might have helped sustain the warming for over 100,000 years, creating a self-perpetuating cycle of heat.
For context, check out this related piece on how Earth turned into a hothouse 250 million years ago and the reasons behind it (https://www.sciencealert.com/earth-became-a-hothouse-250-million-years-ago-and-we-finally-know-why).
Fast forward to today, and our planet is heating up about ten times quicker than in that ancient episode. This accelerated pace could make it even tougher for modern flora to evolve and cope effectively.
Let's travel back in time to understand this better. Plants play a crucial role in stabilizing our climate through carbon sequestration—a vital process where they pull carbon dioxide from the atmosphere during photosynthesis and lock it away in their leaves, trunks, and roots. Think of it like nature's own carbon vault, helping to cool the planet.
But here's where it gets controversial: What if sudden, rapid changes disrupt this delicate balance? Could it mean that in a warming world, plants aren't always the reliable allies we assume them to be?
Delving into how greenery responded to the swift global heat-up 56 million years ago—officially dubbed the Paleocene-Eocene Thermal Maximum, or PETM—is no simple task. To tackle this, we built a sophisticated computer model that simulates plant evolution, movement, and the flow of carbon. We then cross-checked its results against real fossil pollen and plant characteristics from three key locations, piecing together shifts in vegetation like plant height, leaf density, and whether trees shed their leaves seasonally.
These sites included the expansive Bighorn Basin in the US—a vast valley nestled in the northern Rocky Mountains—the North Sea region, and even the Arctic Circle, giving us a global snapshot.
We zeroed in on fossil pollen because it's incredibly useful for this kind of detective work. Pollen grains are produced in huge quantities, they spread far and wide thanks to wind and water, and their tough exteriors resist decay, preserving them well in ancient rocks for scientists to study later.
The evidence paints a picture of significant vegetation upheaval. At mid-latitude spots like the Bighorn Basin, plants seemed less effective at curbing climate change. Pollen records show a move toward smaller species, such as palms and ferns, while the density and thickness of leaves increased, and deciduous trees—those that lose their foliage annually—became scarcer. Soil samples also revealed lower levels of organic carbon.
All signs point to drought-tolerant plants, including those resilient palms, dominating the scene because they managed to keep up with the rising heat. However, these adaptations came at a cost: they were linked to a diminished ability to store carbon in plant tissues and soil.
In stark contrast, the high-latitude Arctic site experienced a different story. Here, vegetation grew taller and more abundant after the warming kicked in. Pollen data highlights how conifer woods gave way to broad-leaved wetland plants, with some subtropical species like palms even sticking around.
Our model, backed by the data, suggests that in these colder regions, plants not only adapted but actually boosted their productivity—meaning they captured and stored more carbon dioxide under the new, warmer conditions. And this is the part most people miss: While the heat stressed plants in some areas, it empowered them in others, creating a patchwork of winners and losers across the globe.
Looking ahead, the vegetation turmoil during the PETM likely hampered land-based carbon storage for 70,000 to 100,000 years, as plants and soils struggled to recapture and hold onto carbon. Our findings indicate that it took a very long time for climate-regulating vegetation to recover, thereby extending the duration of this ancient heatwave.
For another wild example of extreme heat tolerance, read about the 'fire amoeba' that breaks records (https://www.sciencealert.com/extreme-fire-amoeba-smashes-record-for-heat-tolerance).
The PETM's warming exceeded 4°C, which overwhelmed mid-latitude plants' ability to adjust. Now, human-driven climate change is unfolding ten times faster, leaving even less time for adaptation. This prehistoric event underscores the importance of studying how living systems can match the speed of rapid climate shifts to keep carbon sequestration running smoothly.
What do you think—does this mean we should rethink our reliance on natural carbon sinks in the face of modern warming? Or perhaps it's a call to action for faster human interventions? Share your take in the comments; I'm curious to hear agreements, disagreements, or even counterpoints about whether ancient lessons truly apply today.
Vera Korasidis, Lecturer in Environmental Geoscience at The University of Melbourne, and Julian Rogger, Senior Research Associate at the School of Geographical Sciences, University of Bristol.
This piece is republished from The Conversation under a Creative Commons license. Check out the original article here (https://theconversation.com/56-million-years-ago-the-earth-suddenly-heated-up-and-many-plants-stopped-working-properly-270291).
