Why we can’t count on carbon-sucking farms to slow climate change
https://www.technologyreview.com/...hy-we-cant-count-on-carbon-sucking-farms-to-slow-climate-change/
The world’s farmlands do have the capacity to store billions of tons of carbon dioxide in the soil annually, according to a National Academies report last year. But there is still uncertainty concerning which farming techniques work, and to what degree, across different soil types, depths, topographies, crop varieties, climate conditions, and time periods.
It’s unclear whether the practices can be carried out over long periods and on a massive scale across the world’s farms without undercutting food production. And there are significant disagreements about what it will take to accurately measure and certify that farms are actually removing and storing increased amounts of carbon dioxide.
These uncertainties further complicate the well-documented challenges in setting up any reliable carbon offsets program. Studies have frequently found these systems can substantially overestimate reductions, as economic, environmental and political pressures all push toward issuing large numbers of offsets credits. The programs can also create opportunities for gamesmanship and greenwashing that undermine real progress on climate change, observers say.
As Climate Action Reserve looks to ramp up the use of these credits, some fear the group is on the verge of creating a standard that may well invite such behavior.
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The basic idea behind carbon farming, or regenerative agriculture, is that photosynthesis acts as a greenhouse gas pump, pulling CO2 from the air and converting it into sugars stored in leaves, stalks, and roots or excreted into soil. The hope is that farmers can increase the amount of carbon that is left behind in the fields, through practices like planting cover crops between harvests, and drilling seeds instead of continually upturning the soil through tilling.
But the process playing out in California highlights the challenges of establishing reliable standards that can be broadly applied. Such standards certify that the farmers getting paid to carry out the practices are in fact decreasing carbon dioxide in the atmosphere, lending confidence to people or businesses looking to purchase credits.
They’re essential to making offsets work, but hard to get right. Climate Action Reserve, which created the protocols that California largely adopted for the nation’s largest cap-and-trade program, released a draft “soil enrichment protocol” for public comment in April. It was scheduled to bring the standard before its board for a vote this month. But last week, the nonprofit announced a second public comment period after receiving numerous responses, several of which questioned whether the protocol will accurately measure additional levels of carbon uptake.
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The issue is that much of the soil carbon research to date finds that carbon uptake differs widely across soil types and other conditions, not just from region to region, but from plot to plot. So it’s difficult to develop any model “that can account for this inherent variability,” and requires them all to be rigorously tested and reviewed, says Jane Zelikova, chief scientist at the Carbon180 think tank, who also signed the letter. She argues that any modeling must be supplemented with thorough and randomized soil sampling, across fields, at varying depths and over time.
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The better approach could simply be to pay farmers directly to carry out practices to improve soil health and reduce environmental impacts, while thinking of any additional carbon storage as a welcome co-benefit–but not one that’s strictly relied upon to balance out another organization’s greenhouse gas pollution.
“Trying to precisely quantify carbon offsets is almost an impossibly hard problem and one where the deck is stacked against quality outcomes,” says Danny Cullenward, a lecturer at Stanford Law School and policy director of CarbonPlan. “I find it hard to believe we’re going to do a perfect job on this. But that’s what offsets require, because they allow higher emissions elsewhere.