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Global Symposium on Soil Organic Carbon

Key messages

The role of soil organic carbon in climate change and food security

Soil organic carbon (the carbon stored in soil organic matter) is crucial to soil health, fertility and ecosystem services, including food production – making its preservation and restoration essential for sustainable development.

Even as our climate changes, with negative impacts on agriculture, farmers will need to produce up to 60 per cent more food by 2050 as the population swells to nine billion. To meet these needs, soils need to be as productive as possible.

Soils with high carbon content are likely to be more productive and better able to filter and purify water. The water stored in soil serves as the source for 90 per cent of the world’s agricultural production and represents about 65 per cent of fresh water.

Soil organic carbon plays a big role in climate change, presenting both a threat and an opportunity to help meet the targets of the Paris Agreement.

The first meter of soil across the globe holds an estimated 1,417 gigatonnes (Gt) of carbon – almost double the amount in our atmosphere and dozens of times the levels of man-made emissions each year. At greater depths, soil holds three times as much carbon as in the atmosphere.

Soil organic carbon is sensitive to how the soil is managed; poor land management practices cause soils to lose organic matter/carbon and release greenhouse gases.

Already, the degradation of one third of the world’s soils has released up to 78 Gt of carbon into the atmosphere.

  • Deforestation causes about 25 per cent of soil organic carbon loss.
  • Subsoils (soil depths greater than 20-30 cm with mostly lower carbon content), have massive potential for carbon sequestration as they can store up to 760-1520 Gt of additional carbon (Lorenz and Lal, 2005).

Research must focus on the applicability of management practices that allocate more carbon to a greater depth, such as

  • cultivation of deep rooting crops or forages or
  • a technique that moves buried carbon-rich soil material from the surface to a greater depth is deep ploughing; this can raise soil organic carbon levels by over 40 per cent after 5 decades (Alcántara et al., 2016).

Further damage to soil carbon stocks through poor land management would hamper efforts to limit global temperature rise this century and so avoid increased floods, droughts and other negative climate change impacts.

As the climate changes, it is likely that more carbon will be lost to the atmosphere than be sequestered into the soil, resulting in a land carbon–climate feedback loop that could further accelerate climate change.

Of particular concern are hotspots such as peatlands, permafrost and grasslands, which contain the highest amount of soil organic carbon. 

The benefits of action

By sustainably managing soils and rehabilitating degraded land, we can mitigate climate change and improve food security. Carbon sequestration, monitoring and maintenance in soils can also enhance climate resilience, as a healthy amount of soil organic carbon can help plants cope.

Soil rehabilitation in agricultural and degraded soils can remove up to 51 Gt of carbon from the atmosphere.

However, soil organic carbon sequestration is a slow and reversible process. Sustainable soil management practices need to be adopted over the long-term. Governments now need to support land users to implement them. The Voluntary Guidelines for Sustainable Soil Management constitute a tool to guide such a process.

The symposium brings together the science, policy and land-use community to build momentum for preserving soil organic carbon and re-carbonizing degraded soils.

The symposium specifically targets increased action in three areas:

  • Measuring, mapping, monitoring and reporting changes in soil organic carbon;
  • Fostering soil organic carbon sequestration for climate change adaptation and mitigation and land degradation neutrality;
  • Maintaining/restoring soil organic carbon stocks in vulnerable hotspots.