Earth can regulate its own temperature for millennia, a new study has found

Earth’s climate has undergone major changes, from global volcanism to planet-cooling ice ages and dramatic changes in solar radiation. Yet life for the past 3.7 billion years has continued to throb.

Now, a study by researchers at MIT in Scientific progress confirms that the planet has a “stabilizing feedback” mechanism that operates over hundreds of thousands of years to pull the climate back from the brink, keeping global temperatures in a permanent, habitable range.

How does it achieve this? The likely mechanism is “silicate weathering,” a geological process by which the slow and steady weathering of silicate rocks involves chemical reaction which eventually draw carbon dioxide from the atmosphere into ocean sediments, trapping the gas in rocks.

Scientists have long suspected that silicate weathering plays a major role in regulating Earth’s carbon cycle. The mechanism of silicate weathering can provide a geologically constant force carbon dioxide— and global temperatures — under control. But until now there has never been direct evidence of the continuous action of such feedback.

The new findings are based on an examination of paleoclimate data that record changes in average global temperatures over the past 66 million years. The MIT team applied a mathematical analysis to see if the data reveal any patterns characteristic of stabilizing phenomena that have constrained global temperatures over geologic timescales.

They found that there does indeed appear to be a consistent pattern in which the Earth temperature the oscillations slow down over hundreds of thousands of years. The duration of this effect is similar to the timescales over which silicate weathering is predicted to operate.

The results are the first to use actual data to confirm the existence of a stabilizing feedback loop, the mechanism of which is likely to be silicate weathering. This stabilizing feedback would explain how Earth remained habitable through dramatic climatic events in the geological past.

“On the one hand, this is good because we know that today’s global warming will eventually be reversed by this stabilizing feedback,” says Konstantin 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 not fast enough to solve our problems today.”

The study was co-authored by Arnscheidt and Daniel Rothman, professor of geophysics at MIT.

Data stability

Scientists have already seen hints of a climate-stabilizing effect in Earth’s carbon cycle: Chemical analyzes of ancient rocks show that the flow of carbon into and out of Earth’s surface has remained relatively balanced, even with dramatic changes in global temperature. Furthermore, models of silicate weathering predict that the process should have some stabilizing effect on global climate. Finally, the fact of Earth’s continued habitability points to some inherent geological check on extreme temperature fluctuations.

“You have a planet whose climate has undergone such dramatic external changes. Why has life survived all this time? One argument is that we need some kind of stabilizing mechanism to keep temperatures suitable for life,” Arnscheid says. “But such a mechanism has never been demonstrated by data to have consistently controlled Earth’s climate.”

Arnscheid and Rothman sought to confirm whether the stabilizing feedback was indeed at work by looking at data on global temperature fluctuations throughout geologic history. They worked with a range of global temperature records collected by other scientists, from the chemical composition of ancient marine fossils and shells, and from preserved Antarctic ice cores.

“All of this research is only possible because there has been great progress in improving the resolution of these deep-sea temperature records,” notes Arnscheid. “We now have data going back 66 million years, with data points at most 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 uncover patterns in widely variable data sets.

“We realized that this theory makes predictions about what you would expect Earth’s temperature history to look like if there were feedbacks operating on certain time scales,” Arnscheid explains.

Using this approach, the team analyzed the history of average global temperatures over the past 66 million years, looking at the entire period at different time scales, such as tens of thousands of years versus hundreds of thousands, to see if any patterns of stabilizing feedback had emerged within each time scale.

“To a certain extent, it’s like your car is speeding down the street, and when you hit the brakes, you slide for a long time before you stop,” Rothman says. “There is a time scale over which the frictional drag or stabilizing feedback kicks in as the system returns to a steady state.”

Without stabilizing feedbacks, global temperature fluctuations should increase over time. But the team’s analysis revealed a regime where the fluctuations did not increase, meaning that the climate had a stabilizing mechanism before the fluctuations became too extreme. The time scale for this stabilizing effect—hundreds of thousands of years—matches scientists’ prediction for silicate weathering.

Interestingly, Arnscheidt and Rothman found that over longer time scales the data did not reveal any stabilizing feedbacks. This means that there does not appear to be a recurring retreat in global temperatures on time scales longer than a million years. So what has kept global temperatures in check?

“There is an idea that chance may have played a major role in determining why, after more than 3 billion years, life still exists,” Rothman suggests.

In other words, as Earth’s temperatures vary over longer ranges, these fluctuations may simply be small enough in a geological sense to be in a range where a stabilizing feedback, such as silicate weathering, can periodically maintain the climate under control, and more specifically, within a habitable zone.

“There are two camps: some say randomness is a good enough explanation, and others say there must be a stabilizer feedback” says Arnscheid. “We can show, directly from data, that the answer is probably somewhere in the middle. In other words, there was some stabilization, but pure luck probably also played a role in keeping Earth continuously habitable.”

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation, and teaching.