Volcanoes play role in shifting Earth’s climate

Zia Lyle

The history of Earth’s climate has been shaped by volcanoes.

In a recent study published in Science, UT geosciences researchers found that there was more volcanic activity during Earth’s warmer time periods, or greenhouse states. The opposite is also true: Decreased volcanic activity is associated with cooler periods, or icehouse states. The connection lies in the carbon dioxide that volcanoes release when they erupt. 

Lead researcher Ryan McKenzie said the team drew these conclusions by measuring levels of zircon, a mineral tied to volcanic activity, in rock samples.

“We knew the climatic changes occurred, we suspected they were tied to carbon emissions, and we used the mineral zircon as a proxy to track a particular aspect of the carbon fluxes [in relation] to the atmosphere,” McKenzie said.

This study compiled published data on individual mineral ages over the past 720 million years. Brian Horton, a UT geological sciences professor and co-author, said that the absence or presence of carbon dioxide in the atmosphere influences climate. Volcanic activity determines the levels of carbon dioxide in the atmosphere because when rocks are heated during a volcanic eruption, carbon dioxide is released. 

“Everyone has seemed to agree that carbon dioxide is the key,” Horton said. “Whatever is regulating carbon dioxide on planet Earth is driving these greenhouse-to-icehouse conditions, these fluctuations.”

Carbon dioxide in the atmosphere creates a shielding effect that allows solar radiation to enter but not escape, which leads to a warmer climate and a greenhouse state. Horton said that previous climate researchers focused on processes that remove carbon dioxide, while this new study focuses on a mechanism that introduces it into the atmosphere. 

“You have these prominent greenhouse intervals, and when you transition back into icehouse, there is relatively slow removal of carbon dioxide from the atmosphere,” McKenzie said. “This occurs once the volcanic arcs shut down. When you’re not pumping as much carbon dioxide into the atmosphere, it allows for the slow cooling.”

Horton and McKenzie both emphasize that this study focuses on long periods of Earth’s warming and cooling, not current, human-caused climate change. 

“We aren’t addressing this issue directly, but if one looks at the modern day records of how much carbon dioxide is generated by humans compared to volcanoes, it is a large discrepancy,” Horton said. “Humans, right at this moment in this period of geologic time, are generating more atmospheric carbon dioxide than the global volcanic budget.”

Horton said that in addition to focusing on long-term climate cycles, this study emphasized the location of the volcanoes. This study focused on continental arc volcanoes, which are created through the process of subduction, when an oceanic plate descends beneath a continental plate. 

“A volcanic arc that is on the continent is capable of generating and emitting into the atmosphere much more carbon dioxide than the oceanic volcanic systems,” Horton said. 

Horton said one reason for this might be due to the greater presence of carbonate rocks, which emit more carbon dioxide after undergoing magmatism and being heated. 

McKenzie said this study takes a very broad perspective. He and Horton hope that in the future, they can further examine the transitions between warming and cooling and narrow the focus to volcanic activity in specific locations. 

“An interesting next step might be to focus on a few-million-year timeframe in which the Earth goes from one time frame to another,” Horton said. “To see if we see, at that time scale, increases or decreases in volcanic activity and whether or not [shifts in climate] can be pinpointed to a particular continent.”