Scientists have confirmed that “stable feedback” over a period of 100,000 years helps control global temperatures
MASSACHUSETTS ACADEMY OF TECHNOLOGY
Earth’s climate has undergone a number of major changes, from global volcanic activity to planet-cooling ice ages and dramatic changes in solar radiation. And life, over the past 3.7 billion years, continues to function.
Now, a study by MIT researchers at scientific advance confirmed that the planet has a “stabilization feedback” mechanism that works for hundreds of thousands of years to pull the climate back from the brink, keeping global temperatures within a stable, habitable range.
How does it do this? One possible mechanism is “silicate weathering” – a geological process by which the slow and steady weathering of silicate rocks involves chemical reactions that eventually suck carbon dioxide out of the atmosphere. atmosphere and introduced into ocean sediments, trapping gases in rocks.
Scientists have long suspected that silicate weathering plays a key role in regulating the Earth’s carbon cycle. The mechanism of silicate weathering could provide a geologically constant force in keeping carbon dioxide — and global temperatures — under control. But there has never been direct evidence for the continued operation of such feedback until now.
The new findings are based on a study of paleoclimatic data that documents changes in average global temperatures over the past 66 million years. The MIT team applied a mathematical analysis to see if the data revealed any characteristic patterns of stabilizing phenomena that constrain global temperatures over geologic time scales.
They found that there actually seems to be a consistent pattern in which Earth’s temperature fluctuates over a period of hundreds of thousands of years. The duration of this effect is similar to that over which silicate weathering is predicted to take place.
This result is the first to use actual data to confirm the existence of a stability feedback, the mechanism of which is likely silicate weathering. This steady feedback would explain how Earth remained habitable through dramatic climate events in the geologic past.
“On one hand, that’s good because we know that global warming today is ultimately the last,” said Constantin Arnscheidt, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). will be discarded through this stable feedback. “But on the other hand, it would take hundreds of thousands of years to happen, 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 previously seen hints of climate-stabilizing effects on the Earth’s carbon cycle: Chemical analyzes of ancient rocks have shown that carbon flows into and out of the Earth’s surface environment remains relatively equal, even as global temperatures change dramatically. Furthermore, silicate weathering models predict that this process will have some stabilizing effects on the global climate. And finally, the reality of Earth’s long-term habitability points to some inherent geological test for extreme temperature changes.
“You have a planet whose climate is subject to a lot of drastic changes from the outside. Why does life exist all this time? One argument is that we need some sort of stabilizing mechanism to keep the temperature right for life,” Arnscheidt said. “But the data have never demonstrated that such a mechanism has consistently controlled Earth’s climate.”
Arnscheidt and Rothman sought to confirm whether the stabilization feedback really works, by looking at data on global temperature fluctuations over geological history. They worked with a series of global temperature records compiled by other scientists, ranging from the chemical composition of ancient marine fossils and shells, as well as preserved Antarctic ice cores.
Arnscheidt notes: “This whole study was only possible because great progress has been made in improving the resolution of these deep-sea temperature records. “We now have data from 66 million years ago, with data points separated by thousands of years at most.”
Accelerate to a stop
To the data, the team applied the mathematical theory of stochastic differential equations, which is often used to detect patterns in widely fluctuating data sets.
“We found that this theory makes predictions about what the Earth’s temperature history would be like if there were impactful responses over certain time periods,” explains Arnscheidt.
Using this method, the team analyzed the history of average global temperatures over the past 66 million years, looking at entire periods over different time periods, such as tens of thousands of years versus hundreds of thousands of years. years, to see if any consistent feedback patterns emerge over each time period.
“To a certain extent, it’s like your car is speeding down the street and when you step on the brake, you’ll skid for a long time before coming to a stop,” says Rothman. “There is a time scale where frictional resistance or stability feedback kicks in when the system returns to steady state.”
Without a steady response, global temperature fluctuations will increase over time. But the team’s analysis revealed a regime in which fluctuations do not increase, implying that a stabilizing mechanism reigns in the climate before fluctuations become too extreme. The time period for this stabilizing effect — hundreds of thousands of years — coincides with what scientists predicted for silicate weathering.
Interestingly, Arnscheidt and Rothman found that over a longer time period the data did not reveal any stable responses. That is, there does not appear to be any periodic decrease in global temperature over a period longer than a million years. Then, over these longer periods of time, what controlled global temperatures?
“It has been suggested that chance may have played an important role in determining why, more than 3 billion years later, life still exists,” suggested Rothman.
In other words, as Earth’s temperature fluctuates for longer periods of time, these fluctuations can be small enough in the geological sense, to be within the range where stable feedback, such as silicate weathering, can be controlled. periodic climate control, and more, in a habitable area.
“There are two camps,” says Arnscheidt: Some say random chance is a good enough explanation, and others say there must be a steady response. “We can show, directly from the data, that the answer is probably somewhere in the middle. In other words, there has been some stabilization, but pure luck may well have played a role in keeping the Earth continuously habitable.”
This research was supported in part by MathWorks scholarships and the National Science Foundation.
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Written by Jennifer Chu, MIT News Office
MAGAZINE
scientific advance
DOI
ARTICLE TITLE
With or without steady feedback of the Earth system over different time periods
ARTICLE PUBLICATION DATE
16-Nov-2022
With or without steady feedback of the Earth system on different time scales
abstract
The question of how Earth’s climate is stable on a geologic time scale is important for understanding Earth’s history, the long-term consequences of anthropogenic climate change, and the planet’s habitability. Here, we quantify the typical amplitudes of past global temperature fluctuations on a time scale of hundreds to tens of millions of years and use it to assess the presence or absence of reflections. long-term stability in the climate system. On a time scale of 4 to 400 ka, the oscillations do not increase over time, suggesting that stabilizing mechanisms such as the hypothesized “weather feedback” exert superior control in this regime. . Volatility develops on longer time scales, likely due to tectonic or biological changes that cause weather to act as a climate force and feedback. These slower oscillations show no evidence of damping, implying that chance may still play an insignificant role in maintaining Earth’s long-term habitability.
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