Mitigating climate change – every little bit helps

25 June, 2014 by (comments)

If only we could put a little bit of extra carbon into our soils – that could save the planet from overheating, or so the theory goes.

After all, of all the greenhouse gases in the atmosphere that are causing global temperatures to rise, and thus climate change, carbon dioxide (CO2) is by far the most important. Put carbon into the soil, and problem solved. Right?

Not according to a new paper from CIAT senior soil scientist, Rolf Sommer, presenting new predictions of the global climate change mitigation potential of soil organic carbon sequestration on agricultural land.

In it he concludes that, given the various technical difficulties to turn all soils on the globe into carbon sinks, and limitations in the speed of sequestration, soil carbon sequestration has only a humble potential to contribute to the mitigation of climate change.

So what’s new?

If only we could put a little bit of extra carbon into our soils – that could save the planet from overheating, or so the theory goes.

Similar figures on the limited potential of soil organic carbon sequestration have been published before, yet exaggerated hopes on how this alone could do the trick have repeatedly resurfaced.

But, Sommer argues, these don’t take into account the dynamics of soil organic carbon sequestration, which has received little attention.

It is commonly assumed that the introduction of soil carbon sequestration measures on agricultural land, such as conservation agriculture, will continue to fix carbon at a constant rate for some decades into the future. The reality is likely to be different. Soil in any particular place can’t soak up infinite amounts of carbon. There are limits.

So, a global effort to sequester carbon would lead to a steady rise in annual soil organic carbon sequestration, but after two or three decades, amounts of carbon ‘soaked up’ would peak and then slowly drop to zero, as less and less land would become available to turn into a carbon sink and the land already under sequestration reaches it limit. We’d reach a new, albeit higher, organic carbon equilibrium, but would be limited in how much more carbon could be sequestered.

That’s not to say that soils don’t have a role to play in climate change mitigation. In Sommer’s words: “Every little bit helps.”  And certainly over the first decades of concerted effort to sequester carbon in soil this could store up to 9 % of total emissions. There is no single silver bullet to save our climate. More likely, effective climate change mitigation will be the sum of many contributors, including soil organic carbon sequestration.

And, of course, increasing the amount of organic carbon in soils almost automatically increases soil fertility and thus our means to produce enough food for a rapidly growing global population, which is another story….

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Rolf Sommer’s paper – Dynamics and climate change mitigation potential of soil organic carbon sequestration – is free to download from the Journal of Environmental Management until 23 September 2014.

The paper is a contribution to the Climate Change, Agriculture and Food Security (CCAFS) Low Emissions Agriculture research theme, which supports agricultural development that reduces greenhouse gas emissions or sequesters carbon while improving the livelihoods of smallholder farmers.

 

 

 

 

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