France’s “4 per 1000” soil carbon initiative, unveiled with some fanfare at the 2015 United Nations climate conference in Paris, could run into “severe limitations” in its practical application, the UK’s Rothamsted Research Institute concludes in a recent paper in the journal Global Change Biology.
“It’s a bit of a scientific dream, but we have a lot of evidence that supports this dream,” Jean-Paul Moatti, CEO of the French Research Institute for Development, told SciDevNet in December 2015. The project description for 4 Pour 1,000 stated that a 0.4% annual increase in carbon stocks in the top 40 centimetres of soil, plus an end to deforestation, would be enough to offset carbon emissions from human activity.
But the Rothamsted researchers say France has been stepping back from that claim. The impetus behind the initiative was the hope “that if this rate of carbon sequestration was achieved for all soils globally to a depth of 40 centimetres, the carbon removed from the atmosphere would equal annual CO2 emissions from fossil fuels of 8.9 gigatonnes,” they write. But “later enunciations of the initiative” have been more cautious in their projections.
Based on increases in soil organic carbon in 16 long-term experiments in the southeastern UK, the researchers found that letting land lie fallow, retaining crop residues, and adding manure can indeed “increase SOC stocks, often at rates well above the 0.4% per year rate.”
However, they also identify “many situations where these practices cannot be widely adopted, either because they are impractical for farmers or because of wider global issues.” In particular, they note food security concerns that might arise on both local and global levels should too much land be set aside to sequester carbon with the express purpose of climate mitigation.
“A more logical rationale for promoting practices that increase SOC is the urgent need to preserve and improve the functioning of soils, both for sustainable food security and wider ecosystem services,” they conclude.