Volcanoes Act as a Safety Valve for Earth’s Long-Term Climate – Stabilize Surface Temperatures

Scientists at the University of Southampton found that vast chains of volcanoes were responsible for both the emission and then removal of atmospheric carbon dioxide (CO₂) over geological time. This has stabilized the temperatures on the Earth’s surface.

The researchers, working with colleagues from the University of Sydney, Australian National University (ANU), the University of Ottawa and the University of Leeds, have explored the combined impact of processes on solid Earth, oceans and atmosphere over the past 400 million years. Their findings are published in the journal Geosciences of nature.

The natural decomposition and dissolution of rocks on the Earth’s surface is called chemical weathering. This is extremely important because the weathering products (things like calcium and magnesium) are flushed through rivers to the oceans, where they form minerals that trap CO.₂. This feedback mechanism regulates atmospheric CO₂ levels, and in turn the global climate, over geological time.

“In this regard, the weathering of the Earth’s surface serves as a geological thermostat,” says lead author Dr Tom Gernon, associate professor of earth sciences at the University of Southampton and member of the Turing Institute. “But the underlying controls have proven difficult to determine due to the complexity of the Earth system.”

“Many terrestrial processes are interrelated and there are significant time lags between the processes and their effects,” said Eelco Rohling, professor of ocean and climate change at ANU and co-author of the study. “Understanding the relative influence of specific processes within the response of the Earth system has therefore been an intractable problem. “

To unravel the complexity, the team built a new “Earth Network”, incorporating machine learning algorithms and plate tectonics reconstructions. This allowed them to identify the dominant interactions within the Earth system and their evolution over time.

The team found that continental volcanic arcs were the most important factor in the intensity of weathering over the past 400 million years. Today, the continental arcs include chains of volcanoes in, for example, the Andes in South America and the Cascades in the United States. These volcanoes are among the highest and fastest eroding characteristics on Earth. Because volcanic rocks are fragmented and chemically reactive, they are quickly weathered and released into the oceans.

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

The study casts doubt on a long-held concept that Earth’s climatic stability over tens to hundreds of millions of years reflects a balance between weathering of the seabed and continental interiors. “The idea of ​​such a geological standoff between land masses and the seabed as the dominant driver of alteration of the Earth’s surface is not supported by the data,” says Dr Gernon.

“Unfortunately, the results do not mean that nature will save us from climate change,” says Dr Gernon. “Today, atmospheric CO₂ levels are higher than at any time in the past 3 million years, and anthropogenic emissions are approximately 150 times greater than volcanic CO₂ emissions. The continental arcs that appear to have saved the planet in the distant past are simply not present on the scale needed to help counter current CO₂ emissions. “

But the team’s findings still provide critical insight into how the company might handle the current climate crisis. Artificially enhanced rock weathering – where rocks are pulverized and scattered across the ground to speed up chemical reaction rates – could play a key role in safely removing CO₂ of the atmosphere. The team’s results suggest that such schemes can be optimally deployed using calc-alkaline volcanic materials (those containing calcium, potassium, and sodium), such as those found in continental arc environments.

“This is by no means a silver bullet to the climate crisis – we urgently need to reduce CO emissions₂ emissions in accordance with IPCC mitigation pathways, period. Our assessment of weathering feedbacks over long periods of time can help design and evaluate improved weathering patterns at scale, which is just one of the steps needed to address global climate change, ”concludes Dr. Gernon.

Reference: “Global Chemical Weathering dominated by continental arcs since the mid-Paleozoic” by Thomas M. Gernon, Thea K. Hincks, Andrew S. Merdith, Eelco J. Rohling, Martin R. Palmer, Gavin L. Foster, Clément P Bataille and R. Dietmar Müller, 23 August 2021, Nature Geoscience.
DOI: 10.1038 / s41561-021-00806-0