A new study by scientists at the University of Southampton, UK has found that volcanoes have been responsible for stabilising temperatures at Earth's surface and acted as a safety valve for the planet's long-term climate.
The findings of this study were published in the journal Nature Geoscience this week. The researchers 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 along with others 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 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 CO2.
This feedback mechanism regulates atmospheric CO2 levels, and in turn global climate, over geological time, a news release explains.
"In this respect, weathering of the Earth's surface serves as a geological thermostat," Tom Gernon, associate professor in earth science at the University of Southampton, and a fellow of the Turing Institute explains in the release.
"But the underlying controls have proven difficult to determine due to the complexity of the Earth system," added Gernon, who is also the lead author of the study.
"Many Earth processes are interlinked, and there are some major time lags between processes and their effects," Eelco Rohling, professor in ocean and climate change at ANU and the study's co-author explains. "Understanding the relative influence of specific processes within the Earth system response has therefore been an intractable problem," Rohling adds.
To understand the complexity, the team constructed a novel "Earth network", incorporating machine-learning algorithms and plate tectonic reconstructions. This enabled the researchers to identify the dominant interactions within the Earth system, and how they evolved through time, the release explains.
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 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, professor of geochemistry at the University of Southampton and a 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 also 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. "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," Gernon explains in the release. "Unfortunately, the results do not mean that nature will save us from climate change," Gernon adds.
"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," explains Gernon. "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."
But the team's findings still provided critical insights into how society might manage the current climate crisis.