Ancient Climate Secrets – Could Crushing Minerals Stop Global Warming?

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Past global warming events provide insight into the natural mechanisms that regulated Earth’s climate, such as the weathering of rocks, which reduced CO2 emissions into the atmosphere. Today, improving the weathering of rocks could help mitigate climate change, but its effectiveness depends on local geological conditions and the potential for clay formation, which can hinder the process.

Can mixing crushed rock with building soil lower global temperatures? Scientists from the University of Mainz are studying global warming from 40 to 56 million years ago to find answers.

The Earth is getting hotter and the effects have become increasingly apparent around the world this summer. Looking back through geological history, global warming events are not uncommon. About 56 million years ago, during the Paleocene-Eocene Thermal Maximum (PETM), temperatures increased by an average of 5 to 8 degrees Celsius.

This temperature increase was likely caused by increased volcanic activity and the resulting release of large amounts of carbon dioxide into the atmosphere. These elevated temperatures lasted for about 200,000 years.

In 2021, Professor Philip Pogge von Strandmann from the Johannes Gutenberg University Mainz (JGU) had already conducted research into the effect that ultimately led to global cooling and climate recovery after the PETM warming.

In short: Rainwater combines with atmospheric carbon dioxide, resulting in carbon dioxide pickles this caused improved weathering of the rock, releasing calcium and magnesium. Rivers then transported the calcium, magnesium and carbon dioxide to the oceans where the calcium, magnesium – as well as carbon dioxide – came together to form insoluble limestone.

“In other words, there is a feedback effect that helps keep the climate under control. High temperatures accelerate the chemical weathering process of rocks, reducing carbon dioxide levels in the atmosphere, allowing the climate to recover,” said Pogge von Strandmann.

The climate took twice as long to regenerate 40 million years ago

Climate warming occurred again 16 million years after the PETM during the Middle Eocene Climatic Optimum or MECO. Although volcanic activity resulted in the release of approximately the same amounts of carbon dioxide into the atmosphere as during the PETM, it took much longer for the climate to recover.

The warming effect lasted as long as 400,000 years, twice as long as in the PETM. Why was the recovery so slow during that period?

Changes in climate, carbon dioxide concentrations and clay formation during the MECO

The graphs illustrate changes in climate, carbon dioxide concentrations and clay formation during the MECO. Credit: Alexander Krause

Looking for an answer, Pogge von Strandmann and co-authors, including first author Alex Krause, began analyzing 40-million-year-old oceanic carbonates and clay minerals to compare the results with those of comparable 56-million-year-old examples. . “Just like during the PETM, there was also more intensive weathering and erosion in the MECO.

However, 40 million years ago there was much less exposed rock on the Earth’s surface. Instead, the Earth was largely covered by a global rainforest whose soil consisted largely of clay minerals,” the researcher explains. Unlike rock, clay does not age; in fact, it is actually the product of weathering. “Despite the high temperatures, widespread clay soil prevented rocks from becoming effectively weathered, a process known as soil conservation,” the geoscientist said.

Improved weathering for climate protection

How can we use this knowledge in today’s world? “We study paleoclimates to determine whether and how we can positively influence our current climate. One option could be to stimulate the chemical weathering of rocks. To help achieve this, we could plow finely ground rock into our fields,” said Pogge von Strandmann.

The fine-grained rock particles would erode quickly, resulting in the binding of carbon dioxide in the atmosphere, allowing the climate to recover. Negative emission technologies (NETs) such as these, which absorb carbon dioxide, are the subject of intense research around the world. However, if weathering leads to the formation of clay, the effects of the process would be significantly less efficient, as Pogge von Strandmann has discovered.

Clay retains the calcium and magnesium that would otherwise end up in the ocean. The carbon dioxide would continue to flow into the oceans, but would not be bound there and could escape back into the atmosphere. In this case, the weathering effect would have virtually no influence on the climate.

If the rock particles completely dissolve due to weathering, the improved weathering concept would prove to be 100 percent efficient. However, if all weathered materials were processed into clay, this effect would be completely canceled out.

In reality, the true outcome would likely lie somewhere between the two extremes: while there was increased erosion of bedrock in the PETM so that climate normalized more quickly, clay formation was predominant during the MECO. The extent to which the fractured rock dissolves and how much of it is preserved as clay depends on a range of local factors, such as pre-existing levels of clay and rock globally. Thus, to determine whether the process of enhanced weathering is a viable approach, it would first be necessary to find out how much clay is formed during the weathering process at each potential location.

Reference: “Improved clay formation key to preserving the Middle Eocene climate optimum” by Alexander J. Krause, Appy Sluijs, Robin van der Ploeg, Timothy M. Lenton and Philip AE Pogge von Strandmann, July 31, 2023, Natural Geosciences.
DOI: 10.1038/s41561-023-01234-y

Also involved in the project were researchers from University College London and the University of Essex in Great Britain, as well as Utrecht University in the Netherlands.

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