Scientists Discover Volcano’s Role in Regulating Earth’s Long-Term Climate

Researchers from the University of Southampton have found that continuous chains of volcanoes were responsible for both emitting and removing atmospheric carbon dioxide (CO₂) over geological time. This process has stabilized the temperature on Earth’s surface.

The researchers and their counterparts at the University of Sydney, Australian National University (ANU), University of Ottawa and the University of Leeds studied the joint impact of processes in the solid Earth, atmosphere and ocean over the last 400 million years.

The study has been published in the journal Nature Geoscience.

The natural breakdown and dissolution of rocks at the surface of the Earth is called chemical weathering. It is a crucial process because the products of weathering (elements like magnesium and calcium) are flushed into the oceans by rivers. There, they form minerals that are capable of locking up CO₂. This feedback mechanism maintains atmospheric CO₂ levels and the global climate over geological time.

In this respect, weathering of the Earth’s surface serves as a geological thermostat. But the underlying controls have proven difficult to determine due to the complexity of the Earth system.

Dr. Tom Gernon, Study Lead Author and Associate Professor, Earth Science, University of Southampton

According to Eelco Rohling, a Professor in Ocean and Climate Change at ANU and co-author of the study, “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.”

To resolve this complexity, the researchers built a novel “Earth network” by combining machine-learning algorithms and plate tectonic reconstructions. This allowed the researchers to find the dominant interactions within the Earth system, as well as the way in which they evolved over time.

The researchers discovered that continental volcanic arcs were the key influencers of weathering intensity in the last 400 million years. Now, continental arcs are composed of chains of volcanoes, for example, the Cascades in the United States and the Andes in South America.

These volcanoes are considered to be some of the highest and fastest eroding features on Earth. Rapid weathering occurs and the elements are flushed into the ocean because the volcanic rocks are fragmented and chemically reactive.

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.

Martin Palmer, Study Co-Author and Professor of Geochemistry, University of Southampton

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

Dr. Gernon added, “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.”

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.

Dr. Tom Gernon, Study Lead Author and Associate Professor, Earth Science, University of Southampton

However, the study outcomes still offer crucial insights into the way society might manage the existing climate crisis. Artificially improved weathering, where rocks are pulverized and scattered across land to quicken the chemical reaction rates, could have a crucial role in safely removing CO₂ from the atmosphere.

The results propose that such schemes may be applied ideally by using calc-alkaline volcanic materials (those that contain potassium, sodium, and calcium), similar to those 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. 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,” Dr Gernon concluded.

Journal Reference:

Gernon, T. M., et al. (2021) Global chemical weathering dominated by continental arcs since the mid-Palaeozoic. Nature Geoscience. doi.org/10.1038/s41561-021-00806-0.