CO2 from ancient volcanoes was a hidden driver of Earth’s past climate

A new study finds “cryptic carbon” from underground portions of enormous volcanic provinces contributed to climate warming during key moments in Earth’s past.

An international team of geoscientists including Professor Benjamin Mills has discovered that, contrary to present scientific understanding, ancient volcanoes released carbon dioxide (CO2) into the atmosphere from deep within the Earth long past their period of eruptions. 

Led by Rutgers University-New Brunswick, the research team solved a long-standing mystery of the cause of long episodes of warming in the Earth’s climate history. 

The team also included scientists from the University of Oregon, University of Oxford, Oxford, University of California-Davis, Northumbria University and University of Adelaide. 

The study is now published in the journal Nature Geoscience. 

Past warming could predict the future 

For decades, scientists have not understood why the Earth’s atmosphere failed to recover as quickly as expected after the end-Permian mass extinction 252 million years ago – the most severe decrease in biodiversity known to have occurred on Earth.  

The mass extinction has been linked with extreme volcanic eruptions, but even after they stopped, the Earth's climate took nearly 5 million years to stabilize. 

The Earth has natural “climate control systems,” so scientists have questioned why it took so long for the climate to recover. 

Knowing will help them predict how the Earth might recover when human-driven CO2 emissions decrease. 

We think we have figured out an important piece of the puzzle for how Earth’s climate was disrupted, and perhaps just as importantly, how it recovered.

The international research team compared lava with prehistoric, preserved rocks and found evidence for CO2 emissions from volcanoes that could last millions of years after their eruptions had ended. 

Professor Mills used the Spatial Continuous Integration (SCION) global carbon and climate model that he developed at the School of Earth and Environment to test the new CO2 release calculations. 

He added them to the model and found that the new CO2 release estimates were in much better agreement with the geological records. 

The analysis shows that ancient volcanic provinces shut down slowly – though eruptions stopped, magma was still releasing carbon dioxide deep in the crust and mantle. This is known as “cryptic carbon.” 

"We have been struggling to understand the long duration of climate warming seen in many of Earth's past warming events, and our climate and carbon cycle models have not been able to reproduce it,” said Professor Benjamin Mills. 

“With these new estimates of past CO2 release, the models now fit the record. We can conclude that elevated CO2 probably was responsible for these warm climates.” 

“We think we have figured out an important piece of the puzzle for how Earth’s climate was disrupted, and perhaps just as importantly, how it recovered,” said Dr Benjamin Black, lead author from Rutgers University-New Brunswick. 

Can the climate recover?

These findings are part of a multi-year effort funded by the National Science Foundation and Natural Environment Research Council to investigate how cryptic carbon could influence climate recovery. 

This summer, the research team visited northeastern Oregon, where volcanism was linked with climate warming 16 million years ago. 

Team members sampled the glass-like rocks in the mountains, looking for evidence of ancient emissions of carbon dioxide and other gases. 

In the present day, humans release vastly more carbon dioxide than all active volcanoes put together.  

The new findings show how the planet’s climate could stabilise if we reach net zero. 

Finding cryptic carbon, the hidden source of prolonged warming after the mass extinction means that the Earth’s climate controls may work better than previously thought. 

“It could be good news for Earth's recovery after human-driven climate warming,” Dr Black said. “It means that if we stop turning the thermostat up, on geologic timescales, climate can recover.” 

More information

• Top image: Members of the research team examining a large dike—a sheet of magma that transported magma towards Earth’s surface, in this case millions of years ago during the Columbia River Basalt eruptions. Dikes represent the underground root system feeding surface eruptions, and may contain clues to the cryptic CO2 release of ancient eruptions. Credit: Benjamin Black/Rutgers University
• Read ‘Cryptic degassing and protracted greenhouse climates after flood basalt events’ in Nature Geoscience.
• More environment news.