How rain and rocks keep Earth habitable through wild climate changes
Our current climate catastrophe is far from Earth’s first, but for billions of years life has continued to plod along through these ups and downs. MIT scientists have now analyzed 66 million years of climate data and uncovered a stabilizing mechanism that plays out on 100,000-year timescales, keeping global temperatures from swinging beyond the point of no return.
Over its 4.5-billion-year history, Earth has experienced huge volcanic episodes that raised the global temperature, and other times where it spent millions of years as a giant snowball. But no matter how bad things got, the climate would eventually swing back the other way, and though many mass extinctions have occurred, life on Earth has persisted.
But the question remains – how does this happen? What’s stopped Earth from experiencing the runaway greenhouse effect that rendered Venus the hellhole it is today? It’s long been suspected that some kind of feedback mechanism keeps global temperatures within a stable, habitable range, but direct evidence hasn’t been detected in data.
So for the new study, researchers from MIT set out to see if any such signal appeared in ancient climate data records, and what timescale it might be acting on. The team examined several large datasets of global temperature records, including Antarctic ice cores and the chemical composition of tiny marine fossils, stretching back to the extinction of the dinosaurs 66 million years ago.
Next, the scientists applied a mathematical system called stochastic differential equations, which is used to find patterns in datasets that fluctuate on large scales. Using this tool, the team analyzed the average global temperatures over time looking for stabilizing patterns on different timescales, from tens of thousands of years, to hundreds of thousands, and up to millions of years.
“We realized this theory makes predictions for what you would expect Earth’s temperature history to look like if there had been feedbacks acting on certain timescales,” said Constantin Arnscheidt, co-author of the study.
Without any stabilizing feedback mechanism, temperature fluctuations should look more extreme at larger timescales than smaller ones. But the team observed that this wasn’t the case on the scales of millions of years, indicating a stabilizing pattern was occurring on the timescale of hundreds of thousands of years.
The mechanism in question is suspected to be “silicate weathering,” which is thought to be a key part of Earth’s long-term carbon cycle. As rainwater gradually weathers silicate rocks on the planet’s surface, they undergo chemical reactions that increase the rate of carbon they absorb from the atmosphere, which is then carried down into ocean sediments. The more carbon dioxide in the atmosphere, the faster this process occurs, which would act as a brake on a runaway greenhouse effect.
Since models predict that silicate weathering would act on 100,000-year timescales, it’s a good match to be the stabilizing mechanism that the data points to. Intriguingly though, the lack of a mechanism on scales larger than a million years suggests that classic dumb luck may still have a role to play.
“There are two camps: Some say random chance is a good enough explanation, and others say there must be a stabilizing feedback,” said Arnscheidt. “We’re able to show, directly from data, that the answer is probably somewhere in between. In other words, there was some stabilization, but pure luck likely also played a role in keeping Earth continuously habitable.”
To some, this may sound like a get-out-of-jail-free card for our current climate crisis but, of course, the large timescale means humanity – and a huge amount of other organisms – might not live long enough to see it swing back.
“On the one hand, it’s good because we know that today’s global warming will eventually be canceled out through this stabilizing feedback,” said Arnscheidt. “But on the other hand, it will take hundreds of thousands of years to happen, so not fast enough to solve our present-day issues.”
The research was published in the journal Science Advances.