Summary
This is a voluntary international action plan under the Lima-Paris Action Agenda to increase the carbon stock in the top 40 cm (approx. 16 in.) of the world’s soils by an average of 0.4% per year. That is to increase it by just 4 parts per thousand parts of carbon now in the soil. (Carbon is only 27% by weight of a CO2 molecule, so this would sequester considerably more CO2 by weight.) It is not an effort to increase total soil carbon content by 0.4% per year.
France has taken the lead in developing and administering the initiative and to date it has been subscribed to by more than thirty countries since it was launched at COP 21 in Paris in December, 2015. These countries include Australia, Austria, Ethiopia, Germany, Japan, Mexico, Morocco, the Netherlands, New Zealand, the Philippines, Spain, Portugal, the United Kingdom and Uruguay. Almost 200 entities have also now signed the action plan including international organizations, research institutes and universities, financial organizations, producer and agricultural groups and “civil society” organizations (environmental and food security related groups, related companies, etc.) Only a few are U.S. based.
These signatory organizers agree that the “4/1000 annual growth rate of the soil carbon stock intends to show that even a small increase in the soil carbon stock (agricultural soils, notably grasslands and pastures, and forest soils) is crucial to improve soil fertility and agricultural production and to contribute to achieving the long-term objective of limiting the temperature increase to +1,5/2°C.”
They state “The parties to the agreement also state that the objectives and techniques called for are based on “robust scientific research.”
They further conclude that “A 0.4% annual growth rate of the soil carbon stock would make it possible to stop the present increase in atmospheric CO2.” In other words, this approach could achieve “net zero” emissions levels. They estimate that the benefits of implementing the techniques to achieve this would continue for twenty to thirty years.
Parties agree to submit plans for how they will achieve this increase in soil carbon stocks in their countries, share techniques and promote additional research.
Discussion
The international support for this agreement, particularly from developed countries, is a very strong endorsement of the credibility of soil sequestration as a major option for dealing with climate change concerns through a method that is clearly “win/win/win.” It allows for advocates of soil sequestration to simply defer to this international consensus to answer anyone who is skeptical of the power of this approach and instead move directly to discussions of how great the potential is, how it can be implemented and similar issues.
That said, there are limitations to this approach which must be recognized. They are not an argument against using this agreement to advocate for or in defense of the power of soil sequestration but merely a reason to be precise in stating what the agreement claims to be able to accomplish.
One of these limitations actually strengthens the argument for soil sequestration. The calculations cited to support the potential for net negative emissions are based on increasing the carbon store in only the top 40 centimeters ( about 16 inches) of the soil. However, research in the U.S. and around the world clearly shows that Carbon can be and generally is sequestered into much greater depth of the soil, six feet or more in some cases. This means that the potential for sequestration is far greater than the baseline numbers used to support the 4 per Thousand agreement’s conclusion of what is necessary to achieve net zero emissions.
It is common for soil carbon levels to increase by 1% or more after a few years of management techniques that enhance carbon sequestration. This is an increase in the total soil carbon content and not in the existing soil carbon stock. So, to take an example, if the soil carbon content doubles from 1% to 2% on one acre, that would be the equivalent to increasing the soil carbon stock by 0.4% on about 250 acres of other land. It is not unusual to triple and even quadruple soil carbon levels under enhanced management in a relatively short time. In one case documented by the USDA, for example, (Gene Goven farm in North Dakota) soil carbon levels doubled in one year.
How much larger the potential is can be estimated based on research findings. But certainly the scientific consensus that the 4 per Thousand levels of soil sequestration at this relatively shallow depth can achieve the agreement’s goal is very significant. But the fact that sequestration will occur at greater depths as well is especially encouraging. One estimate of the actual immense potential is the estimate by Sachs, et. al. in “Reestablishing the Evolutionary Grassland–Grazer Relationship to Restore Atmospheric Carbon Dioxide to Preindustrial Levels” is that the world’s historic grazing lands alone could sequester all anthropogenic CO2 produced for the past 10,000 years.
Another limitation of the 4 per Thousand agreement is that for forests it is only focusing on the carbon stock in forest soils, not the above ground biomass which invariably accounts for a larger portion of the carbon stored in forests. Including sequestration in forest biomass (which was specifically mentioned in the Paris Agreement) significantly increases the amount of carbon that can be sequestered and reduces the amount of soils in which carbon stocks have to increase by 0.4% per year to achieve net zero emissions.
Finally, the agreement appears to de-emphasize carbon sequestration in cropland soils compared to pasture, grassland and forest soils. Yet, research shows that various agricultural techniques that have a number of beneficial economic and environmental impacts can result in significant carbon sequestration, especially at depths down to 1 foot and below.
In summary, these and similar limitation show that the projections for potential soil carbon sequestration outlined in the 4 per Thousand agenda for action is very conservative.
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