Historical warming events shed light on the Earth’s natural climate stabilization processes, like the weathering of rocks, which decreased levels of carbon dioxide in the atmosphere. Presently, augmenting this rock weathering could potentially aid in counteracting climate change. Nevertheless, its success is contingent on the regional geological attributes and the likelihood of creating clay, which could impede this process.
Is it possible that incorporating pulverized minerals into farm soil could help in reducing global temperature levels? Researchers from Mainz University are examining ancient warming periods from 40 and 56 million years ago for insights.
The planet is experiencing a rise in temperatures, a reality made starkly apparent during this summer’s global heatwaves. Geological records reveal that the Earth has undergone numerous periods of warming. One significant episode, the Paleocene–Eocene Thermal Maximum (PETM), occurred approximately 56 million years ago, causing an average temperature increase of 5 to 8 degrees Celsius.
This dramatic warming was likely triggered by increased volcanic activity that released large quantities of carbon dioxide into the atmosphere. The high temperatures during the PETM endured for around 200,000 years.
In 2021, Professor Philip Pogge von Strandmann from Johannes Gutenberg University Mainz (JGU) investigated what eventually led to a reversal of this warming trend and a return to cooler climatic conditions following the PETM.
Essentially, rainwater reacted with atmospheric carbon dioxide to form carbonic acid, which then accelerated the weathering of rocks, releasing calcium and magnesium. These elements, along with carbonic acid, were carried by rivers to the oceans, where they combined with carbon dioxide to form limestone, an insoluble carbonate.
Pogge von Strandmann remarked, “It acts as a feedback loop that regulates the climate. Higher temperatures speed up the chemical breakdown of rocks, which lowers atmospheric carbon dioxide levels, enabling the climate to stabilize.”
It took twice as long for the climate to recover 40 million years ago
Another period of warming known as the Middle Eocene Climatic Optimum (MECO) took place 16 million years after the PETM. Similar levels of carbon dioxide were emitted due to volcanic activity as with the PETM, yet the climate took much longer to regain equilibrium.
This period of warming lasted an extraordinary 400,000 years, twice as long as the PETM. The question is, why did it take so much longer for the climate to recover during this interval?
Illustrations show the correlations among climatic shifts, carbon dioxide levels, and clay formation throughout the MECO. Credit: Alexander Krause
Pogge von Strandmann and his team, including lead author Alex Krause, started comparing oceanic carbonates and clay minerals from 40 million years ago with those from 56 million years ago. “Similar to the PETM, there was enhanced weathering and erosion during the MECO.
However, less rock was exposed on the Earth’s surface 40 million years ago. Instead, dense global rainforests, with soil predominantly composed of clay minerals, covered the Earth,” said the geoscientist. Unlike rock, clay does not undergo weathering; it is a result of weathering. “Therefore, despite the high temperatures, the prevalence of clay-rich soil inhibited effective rock weathering, a phenomenon known as soil shielding,” he explained.
Using weathering to combat climate change
How might this historical knowledge be applied to the current climate crisis? “We’re examining ancient climates to determine if and how we can exert a positive influence on our current climate. One possibility could be to promote chemical weathering of rocks. This could be facilitated by tilling finely ground rock into agricultural land,” suggested Pogge von Strandmann.
The tiny rock particles would break down quickly, binding atmospheric carbon dioxide and thus aiding climate recovery. Negative emissions technologies (NETs) that capture carbon dioxide are under intensive research worldwide. However, if weathering leads to clay creation, the effectiveness of this process would be greatly diminished, as discovered by Pogge von Strandmann.
Clay traps the calcium and magnesium that should be transferred to the ocean. Consequently, carbon dioxide would keep entering the oceans but not be sequestered, having the potential to return to the atmosphere. In this scenario, the weathering would have a negligible effect on climate.
If the rock particles completely dissolve due to weathering, then the process would be optimally effective. Conversely, if all the weathered material transforms into clay, the process’s impact would be entirely negated.
In practice, the outcome will likely be a balance between these two outcomes: While the PETM saw significant rock erosion that led to quicker climatic normalization, clay predominated during the MECO. The degree to which the crushed rock dissolves versus how much becomes clay depends on various local conditions, including the existing levels of clay and rock. Therefore, to determine if enhanced weathering is a feasible strategy, it is essential to first ascertain the extent of clay produced during the weathering process at each site.
The study also included collaboration with scientists from University College London, the University of Essex in the UK, and Utrecht University in the Netherlands.
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Frequently Asked Questions (FAQs) about rock weathering climate change
Can enhancing rock weathering help combat current climate change?
Enhancing rock weathering may help combat climate change by increasing the chemical breakdown of rocks, which can bind atmospheric carbon dioxide. This method’s efficacy depends on local geological conditions and whether clay, which inhibits weathering, is formed.
How did rock weathering affect ancient global temperatures?
Rock weathering during ancient warming events like the PETM reduced atmospheric carbon dioxide levels. Rainwater and CO2 formed carbonic acid, which weathered rocks and released calcium and magnesium. These elements, combined with CO2 in the oceans, formed limestone, reducing the greenhouse effect.
Why did the climate take longer to stabilize during the MECO compared to the PETM?
During the MECO, which occurred 16 million years after the PETM, extensive global rainforests rich in clay minerals covered Earth. This clay-rich soil shielded the underlying rocks from weathering, a process essential for removing atmospheric carbon dioxide, hence the longer period for climate stabilization.
What might be the modern application of rock weathering for climate recovery?
Modern applications could involve incorporating finely ground rock into agricultural soils to speed up weathering, thereby capturing atmospheric carbon dioxide. This is a form of negative emissions technology (NET), potentially aiding in climate recovery if conditions are optimal for rock dissolution over clay formation.
More about rock weathering climate change
- Understanding the Paleocene–Eocene Thermal Maximum (PETM)
- Middle Eocene Climatic Optimum (MECO) Insights
- Potential of Enhanced Weathering
- Climate Change Mitigation Strategies
- Professor Philip Pogge von Strandmann’s Research
