There’s No Place Like Venus
If or when Earth’s large-scale subduction shuts off in about 3.5 billion years, kneecapping the planet’s ability to bury carbon, Kane and his team’s simulations indicate that the carbon dioxide level in the atmosphere will rise anywhere from 0.1 bars to 0.8 bars. (For reference, the total atmospheric pressure at sea level today is 1 bar, and roughly 0.04% of that, or 0.042 bars, comes from carbon dioxide.) Even in their best-case scenario of a 0.1-bar rise in carbon dioxide, Earth’s surface temperature surpasses 100 degrees Celsius (212 degrees Fahrenheit). The same happens at 0.8 bars, but far more quickly.
Either way, the surface of the world becomes literally boiling hot. Earth will “turn into a post-runaway greenhouse state,” Kane said. “The surface temperature will be too hot for any water. It’ll all boil away.” Nothing sitting on the world’s skin would survive.
Still, Earth won’t get close to the state that Venus is in today. “It’d be Venus lite,” Kane said.
Venus has a 93-bar atmosphere consisting of 96.5% carbon dioxide. Kane and his colleagues’ doomsday machine, no matter how hard they push it, cannot take Earth to those levels. “I was surprised by that,” he said. Because the mantle is sealed off by a stagnant lid, volcanism drops, protecting Earth from a Venus-style roasting better than he thought.
Independent scientists have praised the Reuniting Twins project for challenging prior assumptions and adding significantly to the discussion about the terminal state of rocky planets.
“I like their idea,” Way said, adding that the team’s version of a future Earth “doesn’t sound unreasonable.”
“You end up with a world that’s stinkingly hot,” said Byrne, the Washington University planetary scientist. But, he said, the possibility that it may not be Venusian levels of hot is intriguing.
Kane’s team acknowledged that their model hasn’t considered LIP-style mega-eruptions, and that these events could feasibly add a bounty of trapped carbon to the atmosphere at any point in the future. Maybe Earth gets unlucky and experiences multiple, simultaneous LIP events (though this grows less likely over time, Kane said, as the mantle cools and its churning slows). If so, that scenario could push Earth to be more like Venus than the team’s model suggests.
Uncertainties abound. But if Kane’s team is even broadly correct, it suggests that Venus has a uniquely grim history. Something — perhaps an inundation of lava — burned that planet to the bone. Earth, meanwhile, has so far been unable to bring about its own destruction. Let’s hope that remains the case long into the future.
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