Earth’s climate has undergone some major changes, from global volcanism to ice ages that cooled the planet and dramatic changes in solar radiation. And yet life, for the past 3.7 billion years, has kept on beating.
Now, A Research MIT researchers Scientific progress It confirms that the planet has a “steady feedback” mechanism that works over hundreds of thousands of years to push climate back from the brink, keeping global temperatures within a stable, habitable range.
How does it accomplish this? One potential mechanism is “silicate weathering”—a geological process involving chemical reactions in the slow and steady weathering of silicate rocks that ultimately draws carbon dioxide from the atmosphere and into ocean sediments, trapping the gas in the rocks.
Scientists have long suspected that silicate weathering plays an important role in controlling Earth’s carbon cycle. The mechanism of silicate weathering may provide a geologically constant force in controlling carbon dioxide and global temperature. But direct evidence for the continuous operation of such a feedback has not yet been obtained.
The new findings are based on a study of paleoclimate data that records changes in average global temperature over the past 66 million years. The MIT team applied a mathematical analysis to see if the data revealed any patterns of stabilizing phenomena that control global temperatures on a geological time scale.
They found that there is a consistent pattern of decreasing Earth’s temperature fluctuations over timescales of millions of years. The duration of this effect is similar to the timescales predicted for silicate weathering.
These results are the first to use real data to confirm the existence of a stable feedback, the mechanism of which is silicate weathering. This stable feedback could explain how Earth remained habitable through dramatic climatic events in the geologic past.
“On the one hand, this is good because we know that today’s global warming will eventually be canceled out by this stable feedback,” says Constantin Arnscheid, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “But on the other hand, it would take hundreds of thousands of years to happen, so it’s not fast enough to solve our present-day problems.”
The study was conducted by Arnscheid and Daniel Rothman, professor of geophysics at MIT.
Consistency in data
Scientists have previously seen signs of a climate-stability effect on Earth’s carbon cycle: chemical analyzes of ancient rocks show that the flow of carbon into and out of Earth’s surface environment remains relatively balanced, even through dramatic fluctuations in global temperature. Furthermore, models of silicate weathering predict that this process will have some stabilizing effect on global climate. Finally, the fact of Earth’s stable ecosystem points to some underlying, geological check on extreme temperatures.
“You have a planet whose climate is subject to very dramatic external changes. Why has life lasted so long? “One argument is that we need some kind of stable system to maintain a temperature suitable for life,” says Arnscheidt. “But it has never been proven from the data that such a system consistently controlled Earth’s climate.”
By examining data on global temperature fluctuations through geological history, Arnscheidt and Rothman sought to confirm whether a stable feedback was indeed at work. They worked with a range of global temperature records compiled by other scientists from the chemical composition of ancient marine fossils and shells and from preserved Antarctic ice cores.
“This whole study was only possible because of the great progress made in improving the resolution of these deep-sea temperature records,” notes Arnscheidt. “Now we have data going back 66 million years, and the data points are thousands of years apart.”
Accelerate to a stop
To the data, the team applied the mathematical theory of stochastic differential equations, which is commonly used to reveal patterns in widely fluctuating datasets.
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“We learned that this theory predicts what you would expect Earth’s temperature history to look like if the feedback were operating on fixed time scales,” explains Arnscheidt.
Using this approach, the team analyzed the history of average global temperature over the past 66 million years, considering the entire period at different time scales, such as tens of years and hundreds of thousands of years, to see if any patterns of stabilizing responses had emerged. Each schedule.
“To some extent, it’s like your car speeding down the street, and if you hit the brakes, you skid for a long time before you stop,” says Rothman. “When the system returns to a steady state, there is a time frame where frictional resistance or stabilizing feedback kicks in.”
Without stabilizing feedbacks, global temperature fluctuations must grow over time. But the team’s analysis revealed a regime where the fluctuations did not grow, suggesting that a stable system ruled the climate before the fluctuations became too extreme. The time frame for this stabilization—hundreds of thousands of years—is consistent with what scientists predict for silicate weathering.
Interestingly, on longer time scales, Arnscheidt and Rothman find that the data reveal no stable feedbacks. That is, repeated withdrawals of global temperature do not appear on time scales longer than a million years. On these longer time scales, what keeps global temperatures under control?
“There’s an idea that chance may have played an important role in determining why life still exists after 3 billion years,” Rothman offers.
In other words, when Earth’s temperature fluctuates, these fluctuations may be small enough in a geological sense that stable feedbacks such as silicate weathering are within a range that can control climate over time. More things, within the habitable zone.
“There are two camps: some say random chance is a sufficient explanation, others say there must be a consistent feedback,” says Arnscheidt. “We can show directly from the data that the answer is somewhere in between. In other words, there was some consistency, but pure luck may also have played a role in making the Earth continuously habitable.
This research was supported, in part, by a MathWorks Fellowship and the National Science Foundation.
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