Earth’s climate has undergone some major changes, from global volcanism to ice ages cooling the planet to dramatic changes in solar radiation. And yet life has pounded on for the past 3.7 billion years.
Well, a study by MIT researchers in scientific advances confirms that the planet has a “stabilizing feedback mechanism” that works over hundreds of thousands of years to pull the climate back from the brink and keep global temperatures within a stable, habitable range.
How is this achieved? A likely mechanism is “silicate weathering” – a geological process in which the slow and steady weathering of silicate rock involves chemical reactions that ultimately pull carbon dioxide from the atmosphere into ocean sediments and trap the gas in the rock.
Scientists have long suspected that silicate weathering plays an important role in regulating Earth’s carbon cycle. The mechanism of silicate weathering could provide a geologically constant force to keep carbon dioxide — and global temperatures — in check. But until now there has never been direct evidence of the continuous operation of such feedback.
The new results are based on a study of paleoclimate data that records changes in global mean temperatures over the past 66 million years. The MIT team applied mathematical analysis to determine whether the data revealed distinctive patterns of stabilization phenomena that affected global temperatures on a geologic timescale.
They found that there does appear to be a consistent pattern in which Earth’s temperature variations are dampened over timescales of hundreds of thousands of years. The duration of this effect is similar to the timescales over which silicate weathering is expected to act.
The results are the first to use actual data to confirm the existence of a stabilizing feedback, the mechanism of which is likely silicate weathering. This stabilizing feedback would explain how dramatic climate events in the geological past have kept Earth habitable.
“On the one hand, it’s good because we know that today’s global warming will eventually be reversed by this stabilizing feedback,” says Constantin Arnscheidt, a PhD student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “But on the other hand, it will take hundreds of thousands of years to get there, so not fast enough to solve our problems today.”
The study was co-authored by Arnscheidt and Daniel Rothman, Professor of Geophysics at MIT.
stability in data
Scientists have already seen evidence of a climate-stabilizing effect in the Earth’s carbon cycle: chemical analyzes of ancient rocks have shown that the flow of carbon into and out of the Earth’s surface environment has remained relatively balanced, even during dramatic fluctuations in global temperature. In addition, models of silicate weathering predict that the process should have a stabilizing effect on global climate. Finally, the fact that the earth is permanently habitable points to an inherent geological control of extreme temperature fluctuations.
“You have a planet whose climate has undergone so many dramatic external changes. Why did life survive all this time? One argument is that we need some sort of stabilization mechanism to keep temperatures viable,” says Arnscheidt. “But no such mechanism has ever been proven by data to have consistently controlled Earth’s climate.”
Arnscheidt and Rothman attempted to confirm whether a stabilizing feedback was indeed at work by looking at data on global temperature variations throughout geological history. They worked with a series of global temperature records compiled by other scientists, from the chemical composition of ancient marine fossils and shellfish, and from preserved ice cores from Antarctica.
“This whole study is only possible because there have been great strides in improving the resolution of these deep-sea temperature records,” says Arnscheidt. “Now we have data going back 66 million years, with data points being at most thousands of years apart.”
acceleration to a standstill
To the data, the team applied the mathematical theory of stochastic differential equations, commonly used to uncover patterns in highly volatile data sets.
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“We realized that this theory makes predictions about what the Earth’s temperature history would look like if there had been feedbacks on certain time scales,” explains Arnscheidt.
Using this approach, the team analyzed the history of global average temperatures over the past 66 million years, looking at the entire period across different time scales, e.g. B. Tens of thousands of years versus hundreds of thousands to see if any patterns of stabilizing feedbacks emerged in each time scale.
“To an extent, it’s like your car is speeding down the road and when you hit the brakes, you skid long before you stop,” says Rothman. “There is a time scale over which frictional drag or a stabilizing feedback sets in as the system returns to a steady state.”
Without stabilizing feedbacks, fluctuations in global temperature should increase with timescale. However, the team’s analysis showed a regime in which the variability did not increase, suggesting that a stabilizing mechanism was in place in the climate before the variability became too extreme. The time scale for this stabilizing effect — hundreds of thousands of years — is consistent with what scientists predict for silicate weathering.
Interestingly, Arnscheidt and Rothman found that the data did not reveal any stabilizing feedbacks on longer timescales. That is, there does not appear to be a recurring decline in global temperatures on timescales greater than a million years. What, then, has kept global temperatures under control over these extended periods of time?
“There’s a suggestion that chance may have played a big part in why there’s still life after more than 3 billion years,” says Rothman.
In other words, because the Earth’s temperatures vary over longer distances, these variations may be just small enough, in a geological sense, to be in a range where a stabilizing feedback such as B. silicate weathering that could periodically keep climate in check and more specifically, within a habitable zone.
“There are two camps: Some say that chance is sufficient as an explanation, while others say there must be a stabilizing feedback,” says Arnscheidt. “We can show directly from the data that the answer probably lies somewhere in between. In other words, there was some stabilization, but sheer luck also likely played a role in keeping Earth permanently habitable.”
This research was supported in part by a MathWorks grant and the National Science Foundation.
Republished with permission from MIT News. Read the original article.
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