How does Earth’s "thermostat” control the climate?

Similar to a thermostat, rocks, rain, and carbon dioxide control the Earth’s climate over thousands of years in a process called “weathering.” Now, a team of scientists led by Pennsylvania State University has investigated how this thermostat responds as our planet is warming.

“Life has been on this planet for billions of years, so we know Earth’s temperature has remained consistent enough for there to be liquid water and to support life,” said study lead author Susan Brantley, a professor of Geosciences at Penn State. “The idea is that silicate rock weathering is this thermostat, but no one has ever really agreed on its temperature sensitivity.”

Since many factors contribute to weathering, it has been challenging to use lab experiments to estimate how weathering responds to climate change. To overcome these limitations, the researchers combined laboratory measurements with soil analyses from 45 sites around the globe and a variety of watersheds. 

“When you do experiments in the laboratory versus taking samples from soil or a river, you get different values. So what we tried to do in this research is look across those different spatial scales and figure out how we can make sense of all this data geochemists around the world been accumulating about weathering on the planet. And this study is a model for how we can do that,” Brantley explained.

Weathering contributes to a balancing of CO2 from the atmosphere. Although volcanoes have released massive amounts of CO2 during Earth’s history, this gas has slowly been removed through the process of weathering. In a first step, rain takes the carbon dioxide from the atmosphere and creates a weak acid that falls on the surface of the planet and wears away silicate rocks. Afterwards, the byproducts are carried by rivers and streams to the oceans where this carbon is finally locked away in sedimentary rocks.

“It has long been hypothesized that the balance between carbon dioxide entering the atmosphere from volcanoes and being pulled out by weathering over millions of years holds the temperature of the planet relatively constant,” Brantley said. “The key is when there is more carbon dioxide in the atmosphere and the planet gets hotter, weathering goes faster and pulls more carbon dioxide out. And when the planet is cooler, weathering slows down.”

The analysis revealed that temperature sensitivity measurements in the lab were lower than estimates from soils and rivers and therefore human-made attempts to increase weathering are now crucial to draw sufficient CO2 from the atmosphere. “One idea has been to enhance weathering by digging up a lot of rock, grinding it, transporting it and putting it out in the fields to let weathering happen. And that will work — it’s already working. The problem is, it’s a very slow process,” Brantley concluded.

The study is published in the journal Science Advances.

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By Andrei Ionescu, Earth.com Staff Writer

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