Soils called crucial to combating climate change

As the Trump administration wavers on the U.S. commitment to the Paris Climate Agreement, about 200 scientists, climate activists, farmers, and NGO representatives from around the world convened outside Paris earlier this month to focus on how to bring soil carbon sequestration to scale—and fast.

The event, “Sequestering Carbon in Soil: Addressing the Carbon Threat,” highlighted what’s viewed as the mitigation gap: that even if nations cut carbon emissions to zero, the action would fail to keep global temperature change within the 1.5 to 2 degrees C goal stipulated in the Paris agreement. To get closer to that stated goal, the group believes “carbon sinks,” such as carbon-rich soils, are essential. There is more carbon in soil than in the atmosphere and all the world’s plants combined, despite a loss of more than half of carbon stocks in the world’s farmed soils from over-cultivation, erosion, and desertification. As an added benefit, soil carbon also increases fertility and water retention, bolstering food production.

In a keynote, Christiana Figueres, former executive secretary of the U.N. Framework Convention on Climate Change, likened carbon to the real estate business: “Location, location, location. It’s all about: Where is the carbon? It is a friend or enemy, depending on its location. Carbon in the soil is a friend. Carbon in the atmosphere is an enemy.”

She noted the “happy coincidence” that drawing down carbon benefits both the atmosphere and the local farmer, saying, “Carbon in the soil is a very good proxy for the health of the land, and carbon in the atmosphere is a very good proxy for the lack of health of the planet.”

Different estimates of the potential for soil carbon sequestration were discussed. One benchmark is the 4 per 1,000 Initiative presented at the COP 21 conference on carbon sequestration, which calls for annual soil carbon increases on agricultural lands of 0.4 percent—the equivalent of nearly one-third of current carbon emissions. Speakers highlighted agricultural approaches that build carbon stocks in the soil, including agroforestry, restorative grazing practices, silvopasture (integrated livestock and forestry), and the use of green manure and cover crops, particularly legumes.

This month’s event highlights the emergence of “a new wing of the climate movement”, said Diana Donlon, director of the Food & Climate Campaign at the Center for Food Safety. “We have an opportunity to work in parallel with emissions reductions efforts by scaling up land-based solutions in a way that includes such underrepresented groups as rural communities, smallholder farms, indigenous groups, and women.”

Some scientists called the estimated sequestration rates too low, presenting the risk that soil carbon-building strategies may not be pursued as aggressively as needed. Said Roland Bunch, an agricultural consultant and researcher who has been working in tropical Africa and Central America, “The figures should be at least 50 percent higher and probably 100 percent higher.” According to Australian soil microbiologist Christine Jones, the proposed rates lagged because researchers are primarily evaluating current practices. “They are not looking at the innovators who are getting higher rates,” she said, adding that estimates tend to consider “the top increments of the soil profile,” whereas the largest, most stable carbon increases occur at root level, which in perennial or intercropped systems can be several meters deep. Soil carbon saturation—the theoretical limit for soil carbon uptake—would not be a factor for thousands of years “and certainly not a reason not to do it,” said Jones. 

Policies and financial mechanisms to promote soil carbon sequestration were discussed, as was the need for monitoring methods accessible to small farmers, such as mobile apps. Another theme was the importance of bridging scientific and local knowledge, including indigenous practices. P.K. Nair of the University of Florida called attention to the “importance of multi-species systems that small farmers have been doing for thousands of years.” Such approaches, he said, “are known to be relatively higher [in] potential to sequester soil carbon because species together use resources in a complementary way.”

On the event’s third and final day, a group of participants issued a statement expressing concern that a narrow focus on carbon could lead to a commodification of soil with the unintended consequence of increased corporate control of agricultural lands. An emphasis on improving the livelihoods and sovereignty of small farmers, they wrote, “will in turn lead to healthy soils rich in organic matter and carbon as an added benefit and ultimately contribute to the adaptation to and mitigation of climate change.”

Said Christine Jones: “I would like to see a future in which every piece of agricultural land is functioning as a net carbon sink. If so, we would have this problem solved.”

(Note: An earlier version of this story misspelled Christiana Figueres’ name. It has been corrected.)