WASHINGTON — Volcanoes are nature’s built-in mechanism to stabilize temperatures on the surface of the Earth as they both emit and remove the heat-trapping gas carbon dioxide over geological time, according to a new study.
The findings of the study were published in the journal “Nature Geoscience.”
Scientists at the University of Southampton have discovered that extensive chains of volcanoes have been responsible for both emitting and then removing atmospheric carbon dioxide (CO2) over geological time.
The researchers, working with colleagues at the University of Sydney, Australian National University (ANU), University of Ottawa, and the University of Leeds, explored the combined impact of processes in the solid Earth, oceans, and atmosphere over the past 400 million years.
The natural break-down and dissolution of rocks at the Earth’s surface is called chemical weathering.
It is critically important because the products of weathering (elements like calcium and magnesium) are flushed via rivers to the oceans, where they form minerals that lock up carbon dioxide.
This feedback mechanism regulates atmospheric carbon dioxide levels, and in turn global climate, over geological time.
“In this respect, weathering of the Earth’s surface serves as a geological thermostat,” said lead author 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.”
Many Earth processes are interlinked, and there are some major time lags between these processes and their effects, as explained by Eelco Rohling, Professor in Ocean and Climate Change at the Australian National University and co-author of the study.
“Understanding the relative influence of specific processes within the Earth system response has therefore been an intractable problem,” Rohling said.
To unravel the complexity, the team constructed a novel “Earth network,” incorporating machine-learning algorithms and plate tectonic reconstructions.
This enabled them to identify the dominant interactions within the Earth system and how they evolved through time.
The team found that continental volcanic arcs were the most important driver of weathering intensity over the past 400 million years.
Today, continental arcs comprise chains of volcanoes in, for example, the Andes in South America and the Cascades in the United States.
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.
“It’s a balancing act,” said Martin Palmer, Professor of Geochemistry at the University of Southampton and co-author of the study.
“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 weathering of the seafloor and continental interiors, as explained by Gernon.
“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,” said Gernon.
“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 three 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,”
However, the team’s findings still provided critical insights into how society might manage the current climate crisis.
Artificially enhanced rock weathering—in which rocks are pulverized and spread across the land to speed up chemical reaction rates—could play a key role in safely removing carbon dioxide from the atmosphere.
The team’s findings suggested that such schemes may be deployed optimally by using calc-alkaline volcanic materials (those 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 (Intergovernmental Panel On Climate Change-recommended) mitigation pathways, full stop,” said 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.”
(With inputs from ANI)
Edited by Amrita Das and Krishna Kakani
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