Sink it or lose it: the carbon trade-off

by Rolf Sommer | CIAT (International Center for Tropical Agriculture)
Monday, 20 March 2017 09:26 GMT

In this 2015 file photo, the mud covered hand of local resident Toshiichi Nakazawa, 75, is pictured holding a shovel in Joso, Ibaraki prefecture, Japan. REUTERS/Issei Kato

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* Any views expressed in this article are those of the author and not of Thomson Reuters Foundation.

We must take advantage of the ability to sink carbon in soil if we are to meet the Paris climate targets

In the race to keep climate change in check, our soils are an important ally. A natural carbon sponge, they represent the earth’s largest terrestrial store of this essential, life-giving element.

And if we’re to meet the climate targets laid out in the Paris Agreement, then we must take advantage of the ability to sink carbon in soil, especially because this can offset harmful greenhouse gas emissions elsewhere. 

But while we’re at the forefront of understanding how to make the most of soils to remove carbon dioxide from the atmosphere, our research shows that we’ve still got a way to go before we can realize the full potential of long-term carbon storage – or carbon sequestration. 

Before anything else, we need to be realistic about how much carbon our soils actually can store, how long this will take, how this changes from region to region, and how much this would contribute to climate change mitigation.

Evidence is improving and research advancing, but we still don’t have enough data. Not surprisingly, many aspirations are based on quite a bit of guesswork. 

At the International Center for Tropical Agriculture (CIAT), we have found that even using the best soil management techniques known to science, we can’t seem to store enough carbon – if any – to put a notable dent in global emission figures.

Yet what we do know is that carbon is being lost from soils, especially in the humid tropics, where there is a high turnover of the organic matter in which carbon is found. So we need to focus on reducing – and avoiding - carbon losses before we talk about carbon storage, or sequestration.

One of the contributors to carbon loss is tilling the soil, a common activity on most smallholder farms in developing countries. Here, only very small amounts of organic matter - from crop residues, manure or compost - are dug back into the soil, as these resources are usually in short supply. 

It’s a tall order to call on African smallholders to mitigate greenhouse gas emissions and build carbon in the soil when food insecurity, drought and other challenges are looming. For them, harvesting food – to eat or sell – is the number one priority. And, these farmers already contribute very few emissions to start with, paling in comparison with large commercial farms. 

But our research shows that little changes could have tremendous impacts. For instance, quantifying the climate smartness of best soil protection and restoration practices in Kenya, Ethiopia, Burkina Faso, India and Benin revealed that there are methods that can sustainably intensify farming systems without adding to greenhouse gas emissions. 

If we can convince farmers to adopt small soil conservation practices, we can slow carbon loss down significantly, quickly and without too much effort. The bottom line is that we need more sophisticated management practices than the ones being advocated right now, since sustainable and smart cropping systems have not yet been widely adopted. 

As just one example, good management and applying manure in combination with a judicious use of mineral fertilizers, while also reducing tillage could make all the difference. Yet, there’s a reason such systems have not found their way into farmer’s fields before now. 

Whatever solutions we come up with for turning soils into carbon sinks, they need to be compatible with the realities farmers face. All management practices should boost farm productivity without putting stress on resources, finances or workloads of men and women.

We must both recognize the importance of reducing carbon losses while also finding ways to incentivize farmers to “buy” in to improved ways of managing the soil, like those advocated in conservation agriculture.

And at the same time, we need to look at the bigger picture. There are many other ways to reduce or offset greenhouse gas emissions. For example, livestock are a big contributor to agriculture’s methane emissions. Just improving the quality of livestock feed is enough to reduce this – currently a major lost opportunity. 

We also need to vastly improve wetland conservation and the establishment of new forests, and look at the combined impact of all these measures to capture carbon. And we need to add up these numbers: with the science at our fingertips, by how much can we slow down carbon loss from the soils? What does this mean for climate change mitigation targets globally? 

Only then will we really be able to address the question of how much carbon we can actually sink or store in the soils. Whatever the result, the greater challenge lies in translating these discussions into real benefits for farmers: those facing the frontline impacts of climate change.

Rolf Sommer is a principle soils scientist at the International Center for Tropical Agriculture (CIAT). He will be speaking at the Global Symposium on Organic Carbon in Rome, 21st – 23rd March.

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