Agriculture has a preponderant role in the global carbon accounts, especially when its GHG emissions are added to those from forestry and land use change. Logic of efficacity would ask for intervention first and foremost in this sector, as one of the heaviest contributors. However, this logic is questionable, as it implicitly assumes that each tonne of greenhouse gas that is emitted in the atmosphere is equally harmful, or in other words, that it is worth equal avoidance. Yet, it would be easily agreed that all sectors do not hold equal importance, strategically. For example, a tonne emitted for the manufacture of a vibrating seat, or ice tongs, is easily regarded as less necessary than a tonne emitted to produce medicines, or food. In that sense, agriculture is a crucial sector where emissions will not easily be reduced, given their high degree of necessity (particularly in developing countries) – except through the artificial agency of trade, which is not a solution at global scale.
Mitigation of GHG emissions begins with their accurate measurement. However, carbon accounting is particularly laborious regarding the agricultural sector, due to a number of factors. Firstly, different gasses are emitted – three in the main: 1) nitrous oxide (N2O) from fertilizers and organic matter applied to soils, 2) methane (CH4) from ruminant* digestion and rice cultivation, and 3) carbon oxide (CO2) from direct energy use (farm fuel, power, etc.). These gasses are emitted from different sources that are, apart from farm energy use, all biological, which means: fluctuating, changeable, varying – and sometimes, unpredictable. According to the season, the weather, the plot of land, the measurement location, the type of soil, the surroundings, the crop, the variety or the breed, and the agricultural (past and present) technique, results may vary very significantly – like for any living phenomenon under observation. Agriculture is no exception, even where technical standardization is maximized. This makes extrapolation very delicate, and biologists continue to carry on research on gas exchanges in agroecosystems to draw up more accurate patterns and refine estimations.
If the reduction of food production is not an option, can the agricultural sector increase its efficiency, that is to say, produce more calories per tonne of greenhouse gas?
The contraction of livestock breeding activity (responsible for 14.5% of total human-induced GHG emissions according to the FAO) is regarded – not without reason – as an unavoidable lever. Ruminants are among the main sources of CH4, and more generally, domestic animals need to be fed, which may be regarded as a loss of energy (it requires between 2 and 10 vegetal calories to produce one animal calorie). However, such a consideration is far too simple, and omits a number of critical aspects: first, apart from specialized industrial systems, crop production is most of the time intimately linked to livestock breeding, for the simple reason that ruminants provide to crops the most indispensable nutriment for them: nitrogen. In fact, crops and livestock empirically appeared in history to be highly complementary, the former providing crop residues to the latter, and the latter providing manure (nitrogen) to the former. This has been theorized as “polyculture-livestock systems”, which are found in all regions, proving their effectiveness. Removing livestock breeding would indeed cut direct emissions from ruminants. However, it would also break the ancient association with crops, and lead to the necessary use of synthetic fertilizers to compensate, which in turn would bring their own GHG emissions, from manufacture to field emanations. Moreover, livestock is a keystone species in many pastoral ecosystems (in extensive farming systems), providing crucial ecological services. They also constitute a labour force and sometimes the only way to exploit certain landscapes, such as pastures in the mountains. On the contrary, fertilizers often require mechanization for spreading, and most of all, they heavily disturb carbon and nitrogen cycles on a planetary scale, with severe consequences on biodiversity. While a reduction of meat consumption (and the large-scale livestock breeding that is associated) is certainly a necessary path to mitigate global emissions, there is a need here to distinguish intensive from extensive farming systems, and not forget the numerous services livestock do provide. It should not be considered like any other economic activity, like a factory that could be closed without consequences.
Other mitigation paths exist besides livestock reduction that may be highlighted. The cultivation of pulses (beans, peas, lentils…) constitutes an interesting alternative, as it consists of species that are capable to draw nitrogen directly from the air contained in soil, thus requiring neither fertilizers nor manure. The limitation of tillage and bare soils is another path, as soil working tends to increase gas release. With respect to CO2, reducing mechanization and increasing the energy efficiency of farm infrastructure will help to cut down emissions. Finally, turning to organic agriculture constitutes another mitigation path, as FAO indicates in its Low Greenhouse Gas Agriculture report (2009) that “a conversion to organic farming would mitigate 40% of the world’s agriculture GHG emissions” (p.11).
This important reduction would notably result from organic farming’s higher capacity to retain carbon and nitrogen in its soils. This brings us to the last, but not least, mitigation potential in agriculture that goes beyond the emissions of this single sector: carbon sequestration. A living soil with a high content of organic matter is capable of sequester large amounts of carbon every season. In some cases, pastures show a carbon sequestration rate that is similar to some forests. According to the FAO, combining organic farming with reduced tillage techniques could increase arable soils sequestration rates to at least 500 kg of carbon per hectare per year. Limiting land conversion to bare soils, shifting to conservation soil management and increasing the proportion of permanent crops, pastures and trees within farms could constitute a powerful mitigation policy that moreover would have very positive collateral effects, on biodiversity in particular.
*herbivores such as cattle, goats, sheep.
Hadrien Lantremange, Natural Capital Analyst