Beyond COP 21: Potential and challenges of the "4 per Thousand" initiative

Climate change negotiations at the 21st Conference of the Parties to the United Nations (UN) Framework Convention on Climate Change (COP21) in Paris (November 30 to December 11, 2015) were unique because soil carbon (C) and agriculture were on the agenda for the first time ever since COP meetings started 21 years ago. The “4 per Thousand” proposal calls for a voluntary action plan to enhance soil organic carbon (SOC) content of world soils to a 40 cm (16 in) depth at the rate of 0.4% per year. The strategy is to promote SOC sequestration through adoption of recommended management practices (RMPs) of C farming including conservation agriculture (CA), mulch farming, cover cropping, agroforestry, biochar, improved grazing, and restoration of degraded soils through soil-landscape restoration, etc. Theoretically, the world's cropland soils could sequester as much as 62 t ha−1 (25 tn ac−1) over the next 50 to 75 years (0.8 to 1.2 t ha−1 y−1 [0.3 to 0.5 tn ac−1 yr−1]) with a total C sink capacity of ~88 Gt (~97 billion tn) on 1,400 Mha (3,500 million ac). In addition, there is also SOC sequestration potential of grazing lands, forest lands, and degraded and desertified lands. With global implementation,…