‘We know that today’s global warming will eventually be canceled out through this stabilizing feedback… But on the other hand, it will take hundreds of thousands of years to happen.’
CAMBRIDGE, Mass. — Will climate change really be the end of the world as we know it? Maybe not. But that’s not necessarily good news for Earth’s inhabitants.
Scientists at the Massachusetts Institute of Technology have discovered that the planet has a “stabilizing feedback” system which keeps global temperatures within a steady and habitable range. Although it can take hundreds of thousands of years to complete the process, this mechanism regularly pulls the climate back from the brink of destruction.
“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), in a university release. “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.”
The team notes that Earth has seen a number of dramatic shifts in climate over the last 3.7 billion years. Despite periods of global volcanic activity and planet-wide ice ages, however, Earth continues to bounce back and still supports life.
So, how does the planet regulate its temperature?
The MIT researchers believe the most likely explanation is “silicate weathering” — a geological process where the slow and steady weathering of silicate rocks leads to chemical reactions that draw carbon dioxide out of the atmosphere. These particles enter ocean sediments, trapping the gas in rocks.
Scientists have suspected that silicate weathering contributes to the regulation of Earth’s carbon cycle, but this is the first time researchers have found direct evidence of such a feedback system. Previous studies of ancient rocks have found that the flux of carbon in and out of the Earth’s surface has stayed relatively balanced over time — despite dramatic shifts in global temperatures.
“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 stabilizing mechanism to keep temperatures suitable for life,” says Arnscheidt. “But it’s never been demonstrated from data that such a mechanism has consistently controlled Earth’s climate.”
66 million years of data proves Earth can cool itself off
To confirm that the stabilizing feedback really exists, the team examined global temperature fluctuations over millions of years. Scientists have been compiling this data using the chemical composition of ancient marine fossils and shells, as well as preserved Antarctic ice core samples.
“This whole study is only possible because there have been great advances in improving the resolution of these deep-sea temperature records,” Arnscheidt notes. “Now we have data going back 66 million years, with data points at most thousands of years apart.”
Arnscheidt and co-author Daniel Rothman applied a mathematical theory of stochastic differential equations to this temperature data in order to find patterns in the continuously fluctuating numbers.
“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 explains.
Using this model, study authors looked at different timescales, ranging from tens of thousands to hundreds of thousands of years.
“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,” says Rothman, a professor of geophysics at MIT. “There’s a timescale over which frictional resistance, or a stabilizing feedback, kicks in, when the system returns to a steady state.”
Researchers say that without stabilizing feedbacks, changes in global temperatures should continue to grow over time. However, the study discovered a “regime in which fluctuations did not grow.” This points to some kind of mechanism which reigns in extreme climate shifts. The timescale for this stabilizing effect appears to span hundreds of thousands of years — lining up with scientists’ estimates for silicate weathering.
The stabilizing feedback may be a recent development
Arnscheidt and Rothman say they didn’t find the same planetary pullback during timescales longer than a million years. So, what kept temperatures in check in prehistoric times?
“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 explains.
“There are two camps: Some say random chance is a good enough explanation, and others say there must be a stabilizing feedback,” Arnscheidt adds. “We’re able to show, directly from data, that the answer is probably somewhere in between. In other words, there was some stabilization, but pure luck likely also played a role in keeping Earth continuously habitable.”
The findings appear in the journal Science Advances.