Page 37 - FAO-IPCC Expert meeting on climate change

Greenhouse gas fluxes from agriculture and land systems: a scoping of mitigation options
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Aquaculture produces over 55 million tonnes of fish and shellfish annually, generating high amounts of nitrous oxide emissions. These emissions are predicted to make up approximately 6 percent of anthropogenic nitrous oxide emissions by 2030, representing a major new source of gas to monitor. Likewise, the expansion of shrimp culture has resulted in a significant loss of mangroves (approximately 38 percent) where massive amounts of carbon are stored in the sediments, more than any forest ecosystem in the world. This loss is the most rapid of any type of forest in the world, in some cases, in the order of 2−7 percent per annum.
A key characteristic relatively neglected in GHG emission measurements is the processing of food. To date there are very few studies that analyse emissions throughout the entire food supply chain. A life cycle analysis from the United Kingdom divides up the emissions along the supply chain assigning 40 percent to food production and 30 percent to transport, packaging and processing, both largely derived from the use of fossil energy, with production being less energy intensive than processing. These results are likely to differ depending on the type of food and how it
is produced. As a general rule, food products derived from livestock will tend to have a greater proportion of life
cycle emissions at the production stage, whereas horticultural products would have a greater proportion of lifecycle emissions from the transportation and processing end. But to date, there are no global reviews that fully quantify GHG emissions along the food supply chain, suggesting a critical gap in knowledge.
3.2 Mitigation targets of a 1.5 oC world require negative emissions
The Paris Agreement includes the Bio-Energy with Carbon Capture and Storage (BECCS) incentive, a new technology that removes carbon dioxide from the atmosphere by way of biomass conversion technologies and stores it underground. The inclusion of this factor suggests that it is, indeed, feasible to keep the world warming increase below 1.5 oC . Whether it is realistic to consider BECCS or not is yet unclear. Major research efforts will take place over the coming years to elucidate the problem. Proposed by the International Institute for Applied Systems Analysis as a result of biosphere analyses that revealed unexpectedly higher amounts of emissions as a result of forest fires and methane gas, among others, BECCS aims to sequester such gases. While BECCS is not a typical (or easily accessible) mitigation technology, integrated assessment modelers have relied on it to identify ways to achieve 1.5 o C warming worldwide.
What is clear is that in order to achieve 1.5 o or 2.0 oC global warming, some type of negative emissions are necessary, and BECCS may provide an exceptional solution. One potential course of action lies within the land use sector whereby carbon sequestration can take place through wood burial or similar. Alternatively, the trend of increasing greening activities may be beneficial, although this may cause a reversal in emissions in terms of the magnitude of reforestation and ecological restoration. Finally, it is not clear whether BECCS would have potentially negative consequences for food security.
3.3 Soil carbon sequestration: potential and mitigation options
Soil carbon balance relies on the removal from the atmosphere of CO2 by way of photosynthesis and its incorporation into the plant. A residue then forms, which enters the soil and returns into the atmosphere as CO2 by way of heterotrophic respiration. Soil carbon sequestration (SCS) is simply the management of the soil carbon balance, which is effected by increasing the amount of plant residues that go into the soil and increasing the soil’s organic matter. It
is possible, through conservation agriculture, to reduce the rate of heterotrophic (soil) respiration which releases CO2 into the atmosphere. The duration of SCS is finite as the soil’s organic carbon balance tends to tilt towards equilibrium point. Once SCS has been saturated, little more carbon can be sequestered, despite additional amounts of carbon in the soil (with the exception of peat soils, which are organic).
There are various ways to achieve a rise in the soil carbon balance. These include conservation, no-till and converting land back to forests. The potential for GHG mitigation from soil carbon is the subject of debate in the literature. A white paper, issued by the Rodale Institute of Pennsylvania31 reports that if the world’s agriculture were to shift to organic methods, the amount of carbon sequestration would be equivalent to total fossil fuel emissions. The potential for carbon sequestration depends on the area of the land, as well as the practices that are adopted, some of which rate
31 Rodale Institute. (2014).
FAO-IPCC Expert meeting on climate change, land use and food security