Dr James Hansen – Weathering Heights (a potential climate change carbon capture fix)

  • Published on July 14th, 2020

In 2007 Bill McKibben asked me whether 450 ppm would be a reasonable target for atmospheric CO2, if we wished to maintain a hospitable climate for future generations.  450 ppm seemed clearly too high, based on several lines of evidence, but especially based on paleoclimate data for climate change.

climate change and weathering and the late cretaceous
Map of the continents in the late cretaceous (Wikimedia Commons)

By Dr James Hansen

We were just then working on a paper,[1] Climate sensitivity, sea level and atmospheric carbon dioxide, that included consideration of CO2 changes over the Cenozoic era,[2] the past 65 million years, since the end of the Cretaceous era.  The natural source of atmospheric CO2 is volcanic emissions that occur mainly at continental margins due to plate tectonics (“continental drift”).  The natural sink is the weathering process, which ultimately deposits carbon on the ocean floor as limestone.

David Beerling, an expert in trace gas biogeochemistry at the University of Sheffield, was an organizer of the meeting at which I presented the above referenced paper.  Soon thereafter I enlisted David and other paleoclimate experts to help answer Bill’s question about a safe level of atmospheric CO2, which we concluded was somewhere south of 350 ppm.[3]

Since then, my group at Climate Science, Awareness and Solutions (CSAS), has continued to cooperate with David’s group at the University of Sheffield.  One of the objectives is to investigate the potential for drawdown of atmospheric CO2 by speeding up the weathering process.  In the most recent paper, which was published in Nature last week, David and co-authors report on progress in testing the potential for large-scale CO2 removal via application of rock dust on croplands.

A press release on the paper is available here.

Weathering, nature’s process of removing CO2 from the air, can be sped up by grinding silicate materials into fine dust and spreading it on soils that can otherwise benefit from the addition. Many farmers are accustomed to liming their fields, and have equipment for such purpose.  The silicate particles will dissolve slowly, react with CO2, forming carbonates.  Much of this carbonate will eventually find its way to the ocean, ending up as limestone on the ocean floor.

In order for enhanced weathering to play an important role in CO2 drawdown it will be necessary to demonstrate that it provides a significant benefit in increased soil fertility and crop yield.  If governments also provide a financial incentive via a carbon market, the chances of obtaining large-scale by-in by farmers will be much increased.

Other CO2 drawdown approaches, such as reforestation, are important, but require management to assure that the carbon sink is maintained.  We will need the combination of reforestation, enhanced weathering, and other techniques to draw down atmospheric CO2 to a safe level.

Of course, the most important action required to avoid dangerous climate change is to phase over to carbon-free energies as rapidly as is economically justified.  In that event, it should be possible to bring down atmospheric greenhouse gas levels before slow amplifying climate feedbacks occur, the most dangerous climate impacts need never occur, and we can bend the climate curve back toward the climate within which that humanity and nature lived during the Holocene.

About the Author

Dr. James Hansen directs the Program on Climate Science, Awareness and Solutions of the Earth Institute at Columbia University. The Guardian calls him "The Father of Climate Science" - his 1988 Congressional testimony on climate change helped raise broad awareness of global warming. He is often in the news advocating for a price on carbon and other forms of climate action, divesting from fossil fuels, and helping his grandchildren sue the government over their future. He is the author of "Storms of my Grandchildren".

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