Earth's hidden stabilizing mechanism may help keep the planet habitable - Interesting Engineering

• Researchers find Earth has a "stabilizing feedback" mechanism.
• The mechanism of "silicate weather" helps regulate the planet's carbon cycle.
• The planet balances out extreme climate shifts, according to the new study.

Our planet’s climate is a hot topic for discussion, and with good reason — Earth is the cradle of all our lives. What happens to it affects us and our children directly. But while we’re worried we may be changing its climate now, the history of the planet is rife with major climate cataclysms. It went through periods of boiling heat and ice ages, it was pummeled by radiation and asteroids. Somehow Earth has survived it all so far and a new study from MIT researchers makes the case that Earth has a “stabilizing feedback” mechanism, which over hundreds of thousands of years tends to counterbalance extreme climate shifts, bringing temperatures around the world back into a comfortable range for habitability. 

The scientists pinpointed this mechanism to be “silicate weathering,” which is a geological process that helps regulate our planet’s carbon cycle. It involves the gradual weathering of silicate rocks that can neutralize carbon dioxide emissions from the planet’s crust and mantle by sending them into ocean sediments. It’s an ongoing check on global temperatures.

Revealing patterns

For the study, the MIT team looked at paleoclimate data featuring average global temperatures over the past 66 million years.  A mathematical analysis of the data using stochastic differential equations often used to find patterns within fluctuating datasets, revealed a consistent pattern when swings in Earth’s temperature were balanced out over hundreds of thousands of years. 

This duration corresponded to the times when silicate weathering was believed to be in action.

There were previous indications that some effect exists within the carbon cycle that can stabilize the climate. Studies that performed chemical analyses on ancient rocks demonstrated there was a fluctuation of carbon within Earth’s environment that stayed fairly constant, even throughout major temperature swings.  

It can also be deduced from Earth’s habitability that there are some built-in mechanisms to control temperatures. After all, in the last 800,000 years, the planet has experienced eight cycles of ice ages and warm periods, with the end of the last ice age around 11,700 years ago -- the beginning of the modern climate era. How did the planet make such drastic adjustments? By reaching their conclusion, the new study was the first to use actual data to demonstrate the workings of stabilizing feedback.

The study was co-authored by Constantin Arnscheidt, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) and Daniel Rothman, professor of geophysics at MIT.

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“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,” Arnscheidt shared in a press release.

“To some extent, it’s like your car is speeding down the street, and when you put on the brakes, you slide for a long time before you stop,” added his colleague Rothman. “There’s a timescale over which frictional resistance, or a stabilizing feedback, kicks in, when the system returns to a steady state.”

The one exception

In a fascinating twist on their findings, the scientists found one case where the pattern didn’t seem to hold up — over very long timescales. If you look at gaps of a million years or more, no stabilizing feedbacks seem to be clearly present. So what has kept the temperatures stable over longer periods?

One theory is that it could have been simply chance. As the paper states, chance "may have played a nonnegligible role in maintaining the long-term habitability of Earth." “There’s an idea that chance may have played a major role in determining why, after more than 3 billion years, life still exists,” Rothman stated.

Or perhaps over longer periods, propose the scientists, the fluctuations in temperature remain in the geological range where stabilizing feedbacks like silicate weathering can keep maintaining the climate within the range that can support life. 

More from the researchers

Interesting Engineering (IE) connected with Constantin Arnscheidt for more details on their work.

The following exchange has been lightly edited for clarity and flow.

Interesting Engineering: How would Earth's stabilizing system eventually neutralize the effects of global warming? 

Constantin Arnscheidt: We used data of past global temperature evolution to show that there is a stabilizing feedback on global temperature on 100,000-year timescales. This is consistent with the "silicate weathering feedback" that has been proposed by Earth scientists since at least the 1980s. On timescales of hundreds of thousands of years, CO2 is added to the atmosphere by tectonic processes (e.g. volcanoes) and removed by ocean burial. It turns out that the rate of removal should increase with temperature: so an increased temperature will be countered by additional CO2 removal on long timescales, and vice versa.

IE: Can we wait for Earth to stabilize the climate, or do we have to take action now to address climate change?

Our study suggests that the stabilizing feedback will ultimately neutralize today's global warming. However, this will take hundreds of thousands of years and so it's not fast enough to help with our present-day problems.

IE: Could you elaborate on the role of chance in human survival?

Earth has been able to support life for more than 3 billion years. There is an ongoing debate about how: one argument is that this was entirely due to stabilizing mechanisms, and another that this was entirely due to chance. Our study suggests something in between: there is a stabilizing feedback, but it wasn't all-controlling, and so some amount of pure luck may also have been involved.

Check out their study in Science Advances.

Abstract:

The question of how Earth’s climate is stabilized on geologic time scales is important for understanding Earth’s history, long-term consequences of anthropogenic climate change, and planetary habitability. Here, we quantify the typical amplitude of past global temperature fluctuations on time scales from hundreds to tens of millions of years and use it to assess the presence or absence of long-term stabilizing feedbacks in the climate system. On time scales between 4 and 400 ka, fluctuations fail to grow with time scale, suggesting that stabilizing mechanisms like the hypothesized “weathering feedback” have exerted dominant control in this regime. Fluctuations grow on longer time scales, potentially due to tectonically or biologically driven changes that make weathering act as a climate forcing and a feedback. These slower fluctuations show no evidence of being damped, implying that chance may still have played a nonnegligible role in maintaining the long-term habitability of Earth.

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2022-12-09 09:02:00Z
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