Climate interventions known as geoengineering typically conjure up images of the skies, with sophisticated approaches to deflecting the sun’s rays, or of machines that scour carbon emissions from the air. But some ideas, like ‘enhanced weathering,’ are more earthbound and they, too, are fraught with challenges.
New research from Universität Bremen suggests that enhanced weathering, meant to accelerate a natural process that traps carbon dioxide (CO2) in water and rock, may actually fail to remove as much CO2 as it causes. The net positive effect was demonstrated by Dr. Alexandra Klemme and her colleagues, with results published last week in the journal
Nature Communications.
Weathering removes CO2 from the atmosphere slowly, on chemical and geological timelines that extend across thousands of years. The enhanced weathering idea involves
intentionally crushing rocks into powder so there’s more surface area for the CO2 to bind to rock, forcing the chemical process that traps CO2 to speed up.
“Spreading pulverized rock over land – for example agricultural land – is being discussed as a possible method for reducing atmospheric CO2,” Klemme explains.
It’s been considered a promising strategy, especially in the world’s peatlands. Tropical heat and humidity also accelerate the natural weathering process so, in theory, peatlands have been considered optimal zones for trying to make enhanced weathering work. That’s especially true in Southeast Asia, where peatlands already absorb significant amounts of carbon from the atmosphere but the land use loss to agriculture is changing the equation.
While it’s been thought that enhanced weathering could offset those losses, Klemme’s team found quite the opposite may be true.
Warm and humid conditions further accelerate the weathering process, making tropical peatlands one of the possible target areas for enhanced weathering. About half of these peatlands are located in Southeast Asia. They store huge amounts of carbon and, in their natural state, absorb CO2 from the atmosphere. Today, a large proportion of these peatlands have been converted into agricultural land. “In most cases, this is associated with drainage and leads to peatland transforming from CO2 sinks into CO2 sources,” explains Dr. Klemme. It is hoped that using enhanced weathering in these regions will counteract these CO2 sources. “In addition, enhanced weathering would increase the pH value in the acidic soils. The agricultural industry would welcome this because it increases plant growth.”
Increased pH Value Destabilizes Peat Soils
However, this approach will not have the desired effect, because increasing the pH value through enhanced weathering would destabilize the peat soils. Beyond increasing CO2 emissions from peat soils, Dr. Klemme discovered that this technique resulted in more carbon leaching into rivers, thus raising CO2 emissions from rivers and coastal areas. The research was based on measurements from peat-draining river flows in Indonesia and Malaysia. The Institute of Environmental Physics, the Leibniz Centre for Tropical Marine Research, and Swinburne University have been taking the measurements over the past 10 years. The study shows that an increased pH value could lead to total CO2 emissions exceeding the expected CO2 uptake through enhanced weathering. “Therefore, this method can be ruled out,” says Dr. Klemme.
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