Earth has its own temperature regulating mechanism, says study

PTI

Washington, November 17

Earth has its own stabilising mechanism that can keep global temperatures within a steady, habitable range, helping bring climate back from the brink.

Scientists have long suspected that silicate weathering plays a major role in regulating the Earth’s carbon cycle.

“Silicate weathering” is a geological process by which 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, the study explained.

The mechanism of silicate weathering could provide a geologically constant force in keeping carbon dioxide – and global temperatures – in check. But there has never been direct evidence for the continual operation of such a feedback, until now, the study said.

The results, produced by scientists from Massachusetts Institute of Technology (MIT), US, are the first to use actual data to confirm the existence of a stabilising feedback, the mechanism of which is likely silicate weathering, the study, published in the journal Science Advances, said.

This stabilising feedback would explain how the Earth has remained habitable through dramatic climate events in the geologic past.

“On the one hand, it’s good because we know that today’s global warming will eventually be cancelled out through this stabilising feedback,” said study author Constantin Arnscheidt.

“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.” Scientists have previously seen hints of a climate-stabilising effect in the Earth’s carbon cycle – Chemical analyses of ancient rocks have shown that the flux, or the flow, of carbon in and out of Earth’s surface environment has remained relatively balanced, even through dramatic swings in global temperature.

Models of silicate weathering predict that the process should have some stabilising effect on the global climate. And finally, the fact of the Earth’s enduring habitability points to some inherent, geologic check on extreme temperature swings.

“You have a planet whose climate was subjected to so many dramatic external changes. Why did life survive all this time? One argument is that we need some sort of stabilising mechanism to keep temperatures suitable for life.

“But it has never been demonstrated from data that such a mechanism has consistently controlled Earth’s climate,” Arnscheidt said.

Arnscheidt and Rothman sought to confirm whether a stabilising 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, the study said.

“This whole study is only possible because there have been great advances in improving the resolution of these deep-sea temperature records.

“Now we have data going back 66 million years, with data points at most thousands of years apart,” Arnscheidt noted.

To the data, the team applied the mathematical theory of stochastic differential equations, which is commonly used to reveal patterns in widely fluctuating datasets, the study said.

“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 explained.

Using this approach, the team analyzed the history of average global temperatures over the last 66 million years, considering the entire period over different timescales, such as tens of thousands of years versus hundreds of thousands, to see whether any patterns of stabilising feedback emerged within each timescale.

“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.

“There’s a timescale over which frictional resistance, or a stabilising feedback, kicks in, when the system returns to a steady state,” said Rothman.

Without stabilising feedbacks, fluctuations of global temperature should grow with timescale, the study said.

But the team’s analysis revealed a regime in which fluctuations did not grow, implying that a stabilising mechanism reigned in the climate before fluctuations grew too extreme. The timescale for this stabilising effect – hundreds of thousands of years – coincides with what scientists predict for silicate weathering, the study said.