Science Briefs

Improving the Quantification of Food System Emissions

The Food Climate Partnership (FCP) is a new initiative developed jointly by experts from the NASA Goddard Institute for Space Studies, Columbia University's Center for Climate Systems Research and Center on Global Energy Policy, Agricultural Model Intercomparison and Improvement Project (AgMIP), New York University, and the United Nations Food and Agricultural Organization. This group of experts has developed new analyses on greenhouse gas (GHG) emissions from the food system. This improved quantification of food system emissions can help to provide scenarios used by global climate models (GCMs) to project future changes in Earth's climate. We reported our findings in two companion papers as part of an Environmental Research Letters special issue on "Sustainable Food Systems".

Photo of a farmer in using a roller crimper to terminate cover crops.

A farmer in Evansville Indiana, uses a roller crimper to terminate cover crops. (Credit: Indiana NRCS/Brandon O'Connor via USDA on Flickr)

The food system has a major role to play in climate change mitigation. Better scientific understanding is needed of the processes through which GHGs are emitted — from production to processing, from supply chains and retail to food preparation and waste — as well as insight into how good policies are developed and implemented.

Table of reporting categories of NGHGIs (see caption)

Comparative mapping between reporting categories in National Greenhouse Gas Inventories (NGHGIs), organized by IPCC and FAOSTAT definitions used for food system accounting in this work. (Credit: Tubiello et al., 2021)

Actionable tracking of food system emissions in a new database with both country and global coverage, resulted in an estimated total emissions from the food system amounting to 16 billion metric tons (Gt) of carbon dioxide equivalent (CO2eq) in 2018, an 8 percent increase since 1990. This represents 33 percent of all human-caused GHG emissions.

The global food system represents a larger GHG mitigation opportunity than previously estimated and one that cannot be ignored in efforts to achieve the Paris Agreement goals. Notably, the research finds that the GHG emissions inventories that countries report to the United Nations Framework Convention on Climate Change (UNFCCC) poorly characterize the food system and underestimate its contribution to climate change.

The new country-level database considers GHG emissions linked to farm gate production, land use change at the boundary between farms and natural ecosystems, and supply chains including consumption and waste disposal, to provide improved assessments of food system emission trends at the global, regional, and country levels.

Climate change mitigation and adaptation strategies associated with the food system are likely to be inefficient and possibly counterproductive unless food-related emissions from the various sectors (agriculture, transport, industry, waste, and energy) are conceptualized as a unified whole. The food system and the climate system are deeply intertwined. Better data can help lead to better policies for cutting emissions and protecting the food system from a changing climate.

Impact on the more than 500 million smallholder households around the world is a particularly acute issue in the least-developed countries, where relatively larger shares of the population rely on agriculture for their livelihoods.

One emergent theme is that optimal GHG strategies require a focus on activities both before and after farm production, ranging from the industrial production of fertilizers to refrigeration at the retail level. GHG emissions from these food system activities are growing fast.

Agriculture in developed countries emit large quantities of greenhouse gases, but their share can be obscured by large emissions from other sectors like electricity, transportation and buildings. Looking at the entire food system can not only illuminate opportunities to reduce emissions from agriculture, but also improve efficiency across the whole supply chain with technologies such as refrigeration and storage.

In other key findings, the FCP found that global per capita emissions, which decreased from 1990 to 2010 from 2.9 to 2.2 metric tons CO2eq, were characterized by important differences between developed and developing economies. Per capita emissions in developed countries, at 3.6 metric tons CO2eq in 2018, were nearly twice those in developing countries.

Bar chart of agricultural land emissions, by activity and NGHGI sector (Tubiello et al., 2021)

Agricultural land emissions, by activity and NGHGI sector. (Credit: Tubiello et al., 2021)

Net forest conversion — from natural ecosystems to agricultural croplands or pastures, a proxy for deforestation — remained the largest GHG emission source over this period, at nearly 3 billion metric tons CO2 per year, but declined significantly over time, by over 30 percent from 1990 to 2018.

GHG emissions from domestic food transportation, which were globally 0.5 Gt CO2eq in 2018, have increased by nearly 80 percent since 1990, and nearly tripled in developing countries. GHGs generated by food system energy use — largely carbon dioxide from fossil fuels — along the supply chain amounted to over 4 Gt CO2eq in 2018, an increase of 50 percent since 1990.

Global emissions from food waste disposal, half of which consist of methane, totaled nearly 1 Gt CO2eq in 2018.

Reference

Rosenzweig, C., F. Tubiello, D. Sandalow, P. Benoit, and M. Hayek, 2021: Finding and fixing food system emissions: The double helix of science and policy. Environ Res. Lett., 16, no. 6, 061002, doi:10.1088/1748-9326/ac0134.

Tubiello, F., C. Rosenzweig, G. Conchedda, K. Karl, J. Gütschow, X. Pan, G. Griffiths Obli-Laryea, S. Qiu, J. De Barrios, A. Flammini, E. Mencos Contreras, L. Souza, R. Quadrelli, H. Heiðarsdóttir, P. Benoit, M. Hayek, and D. Sandalow, 2021: Greenhouse gas emissions from food systems: Building the evidence base. Environ. Res. Lett., 16, no. 6, 065007, doi:10.1088/1748-9326/ac018e.

Please address all inquiries about this research to Dr. Cynthia Rosenzweig.

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