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This article was originally published at The conversation. (opens in new tab) The publication contributed the article to Space.com Expert Voices: Op-Ed & Insights.
Dietmar Mueller (opens in new tab)Professor of Geophysics, University of Sydney
Adriana Dutkiewicz (opens in new tab)ARC Future Fellow, University of Sydney
Andrew Merdith (opens in new tab)Research Fellow, University of Leeds
Ben Mather (opens in new tab)Research Fellow, University of Sydney
Christopher Gonzales (opens in new tab)Research Fellow, University of Western Australia
Sabin Zahirovic (opens in new tab)Postdoctoral Research Associate, University of Sydney
Tobias Keller (opens in new tab)Senior Scientist in Computational Geosciences, Swiss Federal Institute of Technology Zurich
Weronika Gorczyk (opens in new tab)The University of Western Australia
Contributor: Jo Condon (opens in new tab)Honorary Researcher, The University of Melbourne
For hundreds of millions of years, the earth’s climate has warmed and cooled with natural fluctuations in the levels of carbon dioxide (CO₂) in the atmosphere. Over the past century, humans have increased the CO₂ content (opens in new tab) to the highest level in 2 million years – exceeding natural emissions – mainly from the burning of fossil fuels, leading to ongoing global warming that may render parts of the earth uninhabitable.
what can be done As geoscientists, we study how natural processes historically returned carbon from the atmosphere to Earth and back to find possible answers to this question.
Our new research (opens in new tab) published in Nature, shows how tectonic plates, volcanoes, eroding mountains, and seafloor sediments controlled Earth’s climate in the geologic past. Harnessing these processes can play a role in maintaining Goldilocks (opens in new tab)“Climate that our planet has enjoyed.
From the Greenhouse to the Ice Age
Greenhouse and ice house climates (opens in new tab) have existed in the geological past. The Cretaceous greenhouse (which existed about 145 million to 66 million years ago) had atmospheric CO₂ levels in excess of 1,000 parts per million, compared to about 420 today, and temperatures that were up to 10 degrees Celsius higher than today.
But Earth’s climate began to cool about 50 million years ago (opens in new tab) during the Cenozoic (opens in new tab)culminating in an ice house climate where temperatures dropped to about 7 degrees C cooler than today.
What triggered this dramatic change in global climate?
Our suspicion was that Earth’s tectonic plates were the culprit. To better understand how tectonic plates store, move and release carbon, we built a computer model of the tectonic ‘carbon conveyor belt’.
The carbon conveyor belt
Tectonic processes release carbon into the atmosphere at mid-ocean ridges—where two plates move apart—allowing magma to rise to the surface and form new ocean crust.
At the same time, at ocean trenches – where two plates meet – plates are being pulled down and pushed back into the depths of the earth. On their way down, they carry carbon back into the Earth’s interior, but also release some CO₂ through volcanic activity.
Our model shows that the Cretaceous greenhouse climate was caused by very fast-moving tectonic plates, which dramatically increased CO₂ emissions from mid-ocean ridges.
During the transition to the Cenozoic ice house climate, tectonic plate movement slowed and volcanic CO₂ emissions began to fall. But to our surprise, we discovered a more complex mechanism hidden in the conveyor belt system, involving mountain building, continental erosion, and the burial of the remains of microscopic organisms on the sea floor.
The hidden cooling effect of slowing tectonic plates in the Cenozoic
Tectonic plates slow down due to collisions, which in turn leads to mountain building, like the Himalayas and Alps that formed over the last 50 million years. This should have reduced volcanic CO₂ emissions, but instead our carbon conveyor belt model showed increased emissions.
We traced their source in carbon-rich deep-sea sediments, which were pushed down to feed volcanoes, increase CO₂ emissions, and reverse the effect of plate slowing.
So what exactly was the mechanism responsible for the decline in atmospheric CO₂?
The answer lies in the mountains, which were responsible for slowing down the plates in the first place, and in the storage of carbon in the deep sea.
As mountains form, they begin to erode. Rainwater containing CO₂ reacts with and breaks down a range of mountain rocks. Rivers carry the dissolved minerals into the sea. Marine organisms then use the dissolved products to build their shells, which eventually become part of carbon-rich marine sediments.
As new mountain ranges formed, more rock was eroded, accelerating this process. Huge amounts of CO₂ were stored and the planet cooled, although some of these sediments were subducted over arc volcanoes with their carbon outgassing.
Rock weathering as a possible carbon dioxide removal technology
That says the Intergovernmental Panel on Climate Change (IPCC). (opens in new tab) Large-scale deployment of carbon removal methods is “inevitable” if the world is to achieve net-zero greenhouse gas emissions.
The weathering of igneous rocks, especially rocks like basalt that contain a mineral called olivine, is very efficient in reducing atmospheric CO₂. Spreading olivine on beaches could absorb up to a trillion tons of CO₂ from the atmosphere (opens in new tab)according to some estimates (opens in new tab).
The rate of current man-made warming (opens in new tab) is such that a very rapid reduction in our carbon emissions is imperative to avoid catastrophic global warming. But geological processes, with a little human help, can also play their part in maintaining Earth’s “Goldilocks” climate.
This study was conducted by researchers from the University of Sydney EarthByte Group (opens in new tab)the University of Western Australia, the University of Leeds and the Swiss Federal Institute of Technology in Zurich use it gplates (opens in new tab) Open access modeling software. This was made possible by Australia’s National Collaborative Research Infrastructure Strategy (NCRIS) via AuScope (opens in new tab) and the Office of the Chief Scientist and Engineer, NSW Department of Industry.
This article is republished by The conversation (opens in new tab) under a Creative Commons license. read this original article (opens in new tab).
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