Some 56 million years ago, just after the Paleocene epoch gave way to the Eocene, the world suddenly warmed. Scientists continue to debate the ultimate cause of the warming, but they agree on its proximate cause: A huge burst of carbon dioxide entered the atmosphere, raising Earth’s average temperature by 7 to 14 degrees Fahrenheit.

As human-generated greenhouse gas emissions cause the world to rapidly warm, this movement is once again under way. Scientists have observed plants shifting toward the poles and upslope. They’ve noted old ecosystems suddenly replaced by new ones, often in the wake of fire, insect outbreaks, drought or other disturbances. They’ve observed an increase in the number of trees dying and watched as a growing number of the world’s biggest and oldest plants, including the baobabs of Africa and the cedars of Lebanon, have succumbed.

So far, many of these changes are subtle, seemingly unrelated to one another, but they are all facets of the same global phenomenon.

Under its worst-case scenario, the Intergovernmental Panel on Climate Change projects that, over the next 100 to 150 years, Earth’s average temperature could rise by roughly the same amount as it did during the PETM. Dramatic vegetational shifts could arrive not in a matter of centuries or millennia, but decades; a 2019 study, for example, projected that Alaska’s vast interior forests will shift from being dominated by conifers to being dominated by broadleaf trees as soon as the middle of this century.

“There’s a whole lot more of this we can expect over the next decades,” said University of Wisconsin-Madison paleoecologist Jack Williams. “When people talk about wildfires out West, about species moving upslope — to me, this is just the beginning.”

Read the full article about plant rearrangement by Zach St. George at Grist.