Earth is able to regulate and stabilize its own temperature across vast timescales – 100,000 years or so on average – even after dramatic shifts in climate caused by ice ages, solar radiation shifts, and intense volcanic activity, new research suggests.
This 'stabilizing feedback' is part of the reason Earth has managed to keep life going for the past 3.7 billion years or so, the team behind the new research says. This feedback has been hypothesized before, but there's now some direct evidence too.
To find that evidence, researchers dug deep into existing paleoclimate data collected over the last 66 million years, applying mathematical modeling to determine whether swings in Earth's average temperatures might be limited by one or more factors.
"You have a planet whose climate was subjected to so many dramatic external changes," says climate scientist Constantin Arnscheidt, from the Massachusetts Institute of Technology (MIT). "Why did life survive all this time?"
"One argument is that we need some sort of stabilizing mechanism to keep temperatures suitable for life. But it's never been demonstrated from data that such a mechanism has consistently controlled Earth's climate."
The team thinks that silicate weathering is a crucial mechanism here: as silicate rocks weather and erode over time, deeper layers of mineral are consistently exposed to the atmosphere. Chemical reactions with the silicates draw carbon dioxide out of the atmosphere, trapping it in rock and ocean sediment.
Higher rates of carbon dioxide entering the atmosphere ramp up weathering activity, increasing the amount of exposed silicates that in turn remove more of the greenhouse gas from the atmosphere, limiting future weathering.
Sure enough, the timescales of the temperature stabilizations match the timescales that silicate weathering operates on, up to around 400,000 years. The record left by fossils and ice cores suggest that this weathering is indeed keeping temperatures in check.
Without this geological feedback mechanism, the researchers suggest, our planet would be going through fluctuations in temperature that get more and more extreme. Knowing how this works is crucial for understanding the planet's past, and its future.
"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 geophysicist Daniel Rothman, from MIT.
"There's a timescale over which frictional resistance, or a stabilizing feedback, kicks in, when the system returns to a steady state."
There's something else going on though: when the team looked at longer timescales, across more than a million years, no such stabilizing feedbacks were observed in the data. It's likely that chance has still played a big part in why life endures.
The researchers conclude that while silicate weathering is enough to provide stabilization in the (relative) short term, we have been lucky that temperature fluctuations over longer periods haven't been severe enough to interrupt this feedback loop.
Of course, the findings also play into predictions for the future of the planet. It's likely that life on Earth is going to be able to weather whatever damage humans do to it – but we may not be here long enough to see it happen.
"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 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."
The research has been published in Science Advances.