Thinking geologically requires an unusual set of habits. These include an awareness that all geographies are ephemeral; an ability to hold in the mind’s eye many versions of the world; and a sense for the rates at which tectonic, climatic, and biological processes remake Earth. Although geology is typically viewed as a backward-looking field, these practices are increasingly being applied not only to the distant past but also to the far future.
An audacious new paper in Nature Geoscience, from eight researchers in the United Kingdom, China, Switzerland, and the United States, uses what we know about Earth’s habits over geologic timescales to imagine the conditions for life 250 million years from now, when tectonics will likely have gathered the world’s land masses into a new supercontinent. The study is the first to use a high-resolution climate model for a future global geography—and the researchers’ predictions do not bode well for us mammals: We would not survive the heat.
How long is 250 million years? The greatest mass extinction of all time, at the end of the Permian period, happened that many years ago, when more than 70 percent of all macroscopic lifeforms succumbed to a hellish combination of volcanically triggered greenhouse warming, ocean acidification, ozone destruction, and a dip in atmospheric oxygen. This was well before the rise and fall of the dinosaurs. Over 250 million years, the supercontinent Pangaea, which had reached its fullest expression in the Permian, scattered into pieces to form the modern continents and ocean basins. It’s about 100 times longer than our species has been around, and far longer than our impact on the climate will be felt by the planet.
Summer dormancy might help land mammals survive in this searing new world.
It’s possible to predict that a new supercontinent will arise 250 million years from now—a reshuffled version of old Pangaea—because tectonic plates move centimeters per year, and don’t tend to change their speed or direction impulsively. The Nature Geoscience paper is based on one particular forecast for the geography of this supercontinent, named “Pangaea Ultima.”
The researchers adapt a climate model developed for the present-day planet to a future Earth that differs not just in the configuration of all landmass into a single giant continent but in its relationship to the sun, which would be older and hotter, emitting 2.5 percent more energy than it does today. Previous projections about life’s long-term future have incorporated the increase in the sun’s output—these suggest that land-based life could thrive for another billion years or so. But the new paper foreshortens that horizon, especially for mammals.
The model makes plausible predictions about global currents in the seas surrounding Pangaea Ultima. With radically different landmass formation, ocean circulation—an important agent of heat redistribution on Earth—will change. Less well constrained are the model’s predictions about weather patterns on land. Continental interiors are always subject to more extreme temperatures than coastlines because they lack the buffering effect of water, but many factors—including mountains, the amount of sunlight the land reflects, and feedbacks between vegetation and precipitation—can profoundly influence weather patterns. The behavior of the future carbon cycle is also a large uncertainty, so the researchers ran their model for a wide range of atmospheric carbon dioxide conditions. They found, disturbingly, that for scenarios with CO2 higher than 280 parts per million (the pre-industrial value), almost all of Pangaea Ultima’s land area would be hotter than 113 degrees Fahrenheit, more than mammalian physiology can tolerate for long.
Strategies like aestivation (summer dormancy, the converse of hibernation) might help land mammals survive in this searing new world, the researchers note. But they don’t seriously consider that heat-adapted mammals might emerge, which is a distinct possibility. Mass extinctions occur when environmental changes outpace evolution. The slow tectonic drift of the continents should allow time for organisms to evolve accordingly. If not, perhaps the destiny of the entire mammal clan is to join the whales and their kin in the water.
The results remind us that we are fortunate to live in a bountiful, clement, and verdant time. We Anthropocene humans should be doing everything we can to make sure other mammal families have the chance to survive 250 million years into the future. If they go extinct in the next century, there will be no descendants around to populate Pangaea Ultima.
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