Less than 250 million years....

Supercontinent’ could make Earth uninhabitable in 250m years, study predicts

Jonathan Watts

The formation of a supercontinent on Earth could wipe out humans and any other mammals that are still around in 250m years, according to a study.

The mass extinction would be caused primarily by heat stress as a result of greater volcanic activity that would put twice as much carbon dioxide into the atmosphere as current levels, an older sun that would emit more radiation and the extent of inland deserts in the tropics.

The supercontinent Pangea Ultima is expected to take shape when all the current continents merge together in the distant future. The paper, which was published on Monday in Nature Geoscience, is the first attempt to model how extreme the climate might become from that geological rearrangement.

Using a UK Met Office climate model and the University of Bristol supercomputer, the simulation also provided tectonic clues to past extinction events and data that could be of use to astronomers looking for other habitable planets.

In the era of Pangea Ultima, the temperature extremes are expected to be dramatic, with more humidity than now along the coasts and extremely arid conditions in the vast inland deserts. In this world, global temperatures could rise 15C (and up to 30C on land) above pre-industrial levels, which would return the world to the extreme heat it last went through in the Permian–Triassic era, 260m years ago, when more than 90% of species were eradicated. Protracted periods of heat in excess of 40C would be beyond the tolerance levels of many life forms.

Mammals have been the world’s great evolutionary success story, particularly since the demise of the dinosaurs during the last great extinction event, but mammals’ ability to adapt to heat may be too slow. That includes humans, which have been on Earth for a relatively short period.

Hominids emerged about 6m years ago when the world was a much cooler place than it had been during the dinosaur period. Although our species has developed remarkably quickly, we would face enormous challenges in the era of Pangea Ultima, assuming we make it through the current self-caused climate crisis and mass extinction of other species.

In addition to the direct impacts of heat, there would be severe food supply problems due to a collapse of vegetation. The paper notes that most plants become stressed at temperatures over 40C and break down completely if exposed to 60C for protracted periods.

The paper’s lead author, Alexander Farnsworth, from the University of Bristol, said the prospect of another extinction event, which includes humans, was a sobering reminder of transience. “The Earth has a very changeable environment. Humans are very lucky with what we have now and we should not be pushing our own climate beyond the cooler climate that we evolved through. We are the dominant species but Earth and its climate decide how long that lasts,” he said. “What comes after is anyone’s guess. The dominant species could be something completely new.”

The authors acknowledge their prediction has a high level of uncertainty due to the ultra-long-term timeframe, but they hope the study, which was initiated during the pandemic lockdown, will provide useful insights into past mass extinction events and the possible habitability of other planets.

Until now, when astronomers have scanned distant galaxies for planets that might provide an alternative home for humans, they have mainly considered the distance from the nearest sun and the presence of water. The new study indicates that tectonics are also an important factor in determining the climate of a planet.

“If Nasa could only send a space shuttle to a single planet, then I would choose one that didn’t have a super continent,” Farnsworth said. “Better to have multiple continents scattered around, as is the case now on Earth.”