If there’s one thing anybody knows about Antarctica, it’s that it’s cold. Yes, people are heating the whole planet. And yes, the world’s biggest glaciers are rapidly turning into ocean. Still, there’s so much ice sitting atop the southernmost continent that we’ll need centuries to melt all of it.
So maybe there was some subtle cold bias that drove routine professional skepticism in the mid-1990s about scientific results suggesting that the South Pole and its environs had surprisingly warm oceans in the dinosaurs’ heyday. Some scientists cast shade again a few years later when research showed that global CO₂ levels 90 millions years ago could have been several times higher than they are today—with consequently higher temperatures, as well.
Any remaining incredulity receded a step further into geological history today with the results published in the journal Nature. Based on an analysis of fossilized plant remnants and meticulous work to reconstruct the prehistoric climate, a large team of European scientists found that a temperate rainforest (think New Zealand) once grew less than 600 miles from the southernmost tip of the earth. The paper helps validate a constellation of previous work and findings from Antarctica and other cold regions—including evidence of crocodile-like Arctic reptiles—all of which points to a once-very hot world.
Having “evidence that we did not have ice sheets, that instead we had a temperate rainforest, is the ground truth we’re looking for,” says Brian Huber, research geologist at the Smithsonian Institution who wasn’t involved in the study.
“I’m pretty jazzed about the paper,” he adds.
The new findings come from drilling near the massive Pine Island and Thwaites glaciers, made vulnerable to melt by the current rising temperatures. Scans of the core samples extracted in 2017 revealed intact roots, fern-tree pollen, moss spores, and the ossified mud that captured them. Between 92 million and 83 million years ago, New Zealand hadn’t yet drifted far away from West Antarctica, and common formations in both areas helped the scientists both date the rock and reconstruct the arrangement of the continents back then.
The researchers commissioned an illustration of what a rainforested Antarctic might have looked like, including flora based on the fossilized roots, pollen and spores and, in the background, a smoking volcano: a nod to the long-lasting hypothesis that massive volcanic outpouring of CO₂ raised the atmospheric concentration of the gas to four to six times the preindustrial benchmark. (Today’s warming is caused by human activity, not volcanoes.)
By studying what was growing in Antarctica during the late Cretaceous Period—about 25 million years before the demise of the dinosaurs—and comparing it to modern plants, the team was able to estimate that the average annual temperature on the continent was about 13° Celsius, or 55° Fahrenheit, despite months spent in darkness every year. That’s an average temperature similar to Beijing, Milan, or Baltimore, with rainfall analogous to Boston or Glasgow, an estimated 44 inches a year. Sea levels might have been 170 meters higher than they are today.
The study was conducted by researchers from German and British institutions, led by Johann Klages, a sedimentologist at the Alfred Wegener Institute in Bremerhaven, Germany. Before now, scientists had little or no reliable data for how the world responds to extreme amounts of CO₂ beyond a latitude of 70° South, he says. This study brings some coverage all the way to 82°S latitude, which in general will help researchers better test and calibrate climate models.
“As we head closer into such high CO₂ conditions—assuming we continue emitting the gas to such extent—we need to understand interconnected feedbacks in these extreme conditions,” Klages says.
Dana Royer, professor of Earth and environmental sciences at Wesleyan University, calls the basic observation of the study “irrefutable” and “profound.”
“The poles were forested during greenhouse times,” he says.