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Of all the ideas that circulated during the recent American Geophysical Union meeting at the Moscone Center, one of the most outlandish-sounding schemes was from a San Francisco entrepreneur who claims he can help conquer climate change by sprinkling pebbles on tropical beaches. The proposal appears, to the uninitiated, to be a first-class boondoggle, but California’s top climate scientists not only support the notion that rocks can sequester carbon, they are clamoring for viable experiments to test the theory.
The idea was mentioned in the 2016 Paris climate agreement, a pledge by nearly 200 nations to cut emissions and prevent global temperatures from rising more than 3.6 degrees Fahrenheit above average preindustrial levels, the point at which warming could begin to have catastrophic consequences. President Trump plans to withdraw the United States from the Paris agreement in 2020.
Studies using crushed volcanic rock on crops have been conducted in the Midwest, Australia, Malaysia and the United Kingdom. In California, UC Davis researchers started field experiments this year with pulverized volcanic rock on 100 acres of alfalfa, corn and almond crops and on rangeland across the Central Valley.
Project leader Ben Houlton, director of the John Muir Institute of the environment at UC Davis, said the study — funded with $5 million from California’s cap-and-trade program — uses a metabasalt taken from the tailings at a local mine and subjects it to the same weathering process as the beach project would, except on land. The rock he uses was selected because it has potassium and zinc in it, which is good for crops. It is pulverized and mixed with the topsoil, where microbial activity causes the weathering that allows carbon dioxide to be consumed.
The idea, Houlton said, is to make the process healthful for crops and useful economically — crop yields have gone up 15% to 20% using the material — providing an incentive for sequestering carbon.
Houlton said his models have shown that farmers could capture between 5 and 10 billion tons of CO2 per year — a little less than a third of what is emitted worldwide — if 75% of earth’s croplands were treated this way. “I think the capacity for a global scale solution is there,” he said, “but there is still a lot of progress to make on the science that is needed to validate this approach.”