Earth’s natural processes can control runaway climate change, MIT finds
Earth has seen some significant changes in climate over its history, including global volcanism, ice ages, and changes in solar radiation.
[Apr. 27, 2023: Staff Writer, The Brighter Side of News]
Research confirms that the planet harbors a “stabilizing feedback” mechanism that acts over hundreds of thousands of years to pull the climate back from the brink. (Credit: Shutterstock)
The Earth has seen some significant changes in climate over its history, including global volcanism, ice ages, and changes in solar radiation. Despite this, life has continued for the last 3.7 billion years. This is due in part to a stabilizing feedback mechanism, which is the subject of a recent study published in Science Advances by researchers from the Massachusetts Institute of Technology (MIT).
The research confirms that the planet possesses a mechanism that operates over hundreds of thousands of years to stabilize the climate and keep global temperatures within a steady and habitable range.
The researchers propose that the mechanism of “silicate weathering” is a likely explanation for this feedback. Silicate weathering is a geological process whereby the slow and steady weathering of silicate rocks involves chemical reactions that ultimately draw carbon dioxide out of the atmosphere and into ocean sediments, trapping the gas in rocks.
Scientists have long suspected that silicate weathering plays a major role in regulating the Earth’s carbon cycle. This mechanism could provide a geologically constant force in keeping carbon dioxide and global temperatures in check. However, until now, there has been no direct evidence for the continual operation of such a feedback.
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The researchers used a mathematical analysis to see whether paleoclimate data that recorded changes in average global temperatures over the last 66 million years revealed any patterns characteristic of stabilizing phenomena that reined in global temperatures on a geologic timescale.
They found that indeed there appears to be a consistent pattern in which the Earth’s temperature swings 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 predicted to act.
These 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 the Earth has remained habitable through dramatic climate events in the geologic past.
Root mean square temperature fluctuations ΔTrms as a function of time scale Δt (Materials and Methods) for five different paleotemperature time series and three nonoverlapping segments of the data from (36). Power-law scalings with fixed exponents H are shown as guides for interpretation. (CREDIT: Science Advances)
“On the one hand, it’s good because we know that today’s global warming will eventually be canceled out through this stabilizing feedback,” says Constantin Arnscheidt, a graduate 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 happen, so not fast enough to solve our present-day issues.”
Chemical analyses of ancient rocks have shown that the flux of carbon in and out of Earth’s surface environment has remained relatively balanced, even through dramatic swings in global temperature. Furthermore, models of silicate weathering predict that the process should have some stabilizing effect on the global climate. Finally, the fact of the Earth’s enduring habitability points to some inherent, geologic check on extreme temperature swings.
A system with multiple partially stabilizing feedbacks can display the same behavior observed in the data. In our simple conceptual model, Earth’s surface temperature T is given by the sum of some stochastic processes with stabilizing feedbacks and some without. (CREDIT: Science Advances)
Arnscheidt and Rothman sought to confirm whether a stabilizing feedback has indeed been at work by looking at data of global temperature fluctuations through geologic history. They worked with a range of global temperature records compiled by other scientists, from the chemical composition of ancient marine fossils and shells, as well as preserved Antarctic ice cores.
“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,” Rothman says. “There’s a timescale over which frictional resistance, or a stabilizing feedback, kicks in, when the system returns to a steady state.”
The observation that fluctuation amplitudes increase like a random walk again beyond 400 ka, even though the silicate weathering feedback remains active, could potentially be understood as follows. Considering Earth’s “weathering curve,” it is clear how changes such as an increase in weatherability can move the steady state that silicate weathering establishes. (CREDIT: Science Advances)
Without stabilizing feedbacks, fluctuations of global temperature should grow with timescale. But the team’s analysis revealed a regime in which fluctuations did not grow, implying that a stabilizing mechanism reigned in the climate before fluctuations grew too extreme. The timescale for this stabilizing effect, hundreds of thousands of years, coincides with what scientists predict for silicate weathering.
In other words, as the Earth’s temperatures fluctuate over longer stretches, it’s possible that the lack of stabilizing feedbacks means chance events, such as meteor impacts or volcanic eruptions, play a larger role in determining the ultimate fate of life on Earth. However, further research is needed to fully understand the mechanisms at play over these longer timescales.
The observation that fluctuation amplitudes increase like a random walk again beyond 400 ka, even though the silicate weathering feedback remains active, could potentially be understood as follows. On time scales below about 400 ka, silicate weathering acts as a feedback, driving the system toward a steady state. On longer time scales, the steady state itself moves, and weathering acts as a forcing. There is still damping toward the steady state; the key point is that there is no damping on the motion of the steady state itself. (CREDIT: Science Advances)
The implications of the study are significant. While it confirms the existence of a stabilizing feedback mechanism that has kept the Earth’s climate habitable for billions of years, it also highlights the fact that this mechanism operates on timescales much longer than those that humans are used to dealing with.
The current global warming trend caused by human activities is occurring on a timescale of decades and centuries, whereas the stabilizing feedback mechanism identified in this study operates on timescales of hundreds of thousands of years.
This means that while the stabilizing feedback mechanism is reassuring in the sense that it suggests that the Earth’s climate is not completely at the mercy of external forces, it also underscores the urgency of taking action to reduce greenhouse gas emissions and limit the extent of future climate change.
The study’s authors caution that the stabilizing effect of silicate weathering is not infinite, and that continued greenhouse gas emissions could overwhelm the mechanism, leading to a runaway greenhouse effect and catastrophic climate change.
“The Earth has this self-stabilizing mechanism that’s kept it habitable for so long, but there are limits to it,” Arnscheidt says. “If we push too hard, we might drive the Earth to a different state, one that’s not suitable for us.”
The MIT study provides compelling evidence for the existence of a stabilizing feedback mechanism that has kept the Earth’s climate habitable for billions of years. The mechanism, which is likely due to silicate weathering, acts over timescales of hundreds of thousands of years to draw carbon dioxide out of the atmosphere and regulate global temperatures.
While the study’s findings are reassuring in the sense that they suggest the Earth’s climate is not completely at the mercy of external forces, they also highlight the need for urgent action to reduce greenhouse gas emissions and limit the extent of future climate change. Continued emissions could overwhelm the stabilizing mechanism identified in this study, leading to a runaway greenhouse effect and catastrophic climate change.
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