Enormous volcano chains ‘acted as Earth’s safety valve’ increasing and decreasing CO2, research suggests

With the impacts of the global climate crisis worsening, it would be quite handy if our planet had its own means of regulating greenhouse gas levels and average temperatures… It turns out such a system does exist – sort of.

New research indicates that extensive chains of volcanoes, which occur in many parts of the earth, have previously played a major role in stabilising temperatures on the Earth’s surface, according to scientists at the University of Southampton.

Over the past 400 million years, processes involving the natural breakdown and dissolution of rocks on the Earth’s surface have trapped and stored large volumes of CO2, but volcanic eruptions also emit large quantities of CO2. Researchers therefore have described the process as a “balancing act”, helping to maintain conditions favourable to life.

The breakdown of rocks is called “chemical weathering”, and the scientists said it is “critically important”, because during the process, elements such as calcium and magnesium are produced and are washed via rivers back into the oceans, where they form minerals which lock up CO2.

The scientists said this feedback loop regulates atmospheric CO2 levels, and in turn, the global climate, over geological time.

“In this respect, weathering of the Earth’s surface serves as a geological thermostat”, said lead author Dr Tom Gernon, associate professor in Earth science at the University of Southampton, and a fellow of the Turing Institute.

“But the underlying controls have proven difficult to determine due to the complexity of the Earth system”.

Eelco Rohling, professor in ocean and climate change at ANU and co-author of the study, said: “Many Earth processes are interlinked, and there are some major time lags between processes and their effects.”

“Understanding the relative influence of specific processes within the Earth system response has therefore been an intractable problem.”

In order to unravel the complexity, of volcanoes’ cause and effect on our planet’s climate, the team constructed brand new computer models and plate tectonic reconstructions.

They said this enabled them to identify the key interactions within the Earth system, and how they evolved through time.

The research revealed that continental volcanic arcs were the most important driver of weathering intensity over the past 400 million years.

Today, continental arcs make up chains of volcanoes in places such as the Andes in South America, and the Cascades in the US.

These volcanoes are some of the highest and fastest eroding features on Earth. Because the volcanic rocks are fragmented and chemically reactive, they are rapidly weathered and flushed into the oceans.

Martin Palmer, a professor of geochemistry at the University of Southampton and co-author of the study, said: “It’s a balancing act. On one hand, these volcanoes pumped out large amounts of CO2 that increased atmospheric CO2 levels. On the other hand, these same volcanoes helped remove that carbon via rapid weathering reactions.”

The study casts doubt on a long-held concept that Earth’s climate stability over tens to hundreds of millions of years reflects a balance between the weathering of the seafloor and continental interiors.

“The idea of such a geological tug of war between the landmasses and the seafloor as a dominant driver of Earth surface weathering is not supported by the data,” Dr Gernon said.

Also, the research team stressed that these processes will not be sufficient in any way to have an impact in undoing or offsetting the damage done by humans to the environment.

Dr Gernon said: “Unfortunately, the results do not mean that nature will save us from climate change.”

“Today, atmospheric CO2 levels are higher than at any time in the past 3 million years, and human-driven emissions are about 150 times larger than volcanic CO2 emissions.

“The continental arcs that appear to have saved the planet in the deep past are simply not present at the scale needed to help counteract present-day CO2 emissions.”

Nonetheless, the researchers said their findings still provide critical insights into how society might manage the current climate crisis.

Artificially enhanced rock weathering – where rocks are pulverised and spread across land to speed up chemical reaction rates – could play a key role in safely removing CO2 from the atmosphere.

The team’s findings suggest that such schemes may be deployed optimally by using calc-alkaline volcanic materials – containing calcium, potassium and sodium – like those found in continental arc environments.

“This is by no means a silver bullet solution to the climate crisis – we urgently need to reduce CO2 emissions in line with IPCC mitigation pathways, full stop,” said Dr Gernon.

“Our assessment of weathering feedbacks over long timescales may help in designing and evaluating large-scale enhanced weathering schemes, which is just one of the steps needed to counteract global climate change.”

The research is published in the journal Nature Geoscience.