Quantifying Agroecosystem Greenhouse Gas Emissions in Spain, 1900-2008

Editor’s Note: This is part of a monthly series showing the work of the Sustainable Farm Systems project

Agricultural production (including crop, livestock and forestry) is a major contributor to anthropogenic greenhouse gas (GHG) emissions, even considering that most estimations do not take into account all processes directly and indirectly involved. Fossil fuel use in fertilizer production, mechanization and irrigation are important contributors to agricultural GHG emissions, but the overall emission balance is dominated by non-fossil fuel emissions, including mainly methane (CH₄) from ruminants, manure and rice fields, nitrous oxide (N₂O) from soils and manure, and biogenic carbon dioxide (CO₂) from deforestation. This pattern distinguishes agriculture from other activities such as transport, buildings or industry, in which most emissions can be more directly traced to fossil fuel use. This raises the question: What has been the effect of agricultural industrialization on the carbon intensity of food production and on the total amount of agricultural GHG emissions? As part of the international project “Sustainable Farm Systems: Long-Term Socio-Ecological Metabolism in Western Agriculture, 1700-2000”, the Agro-ecosystems History Laboratory of University Pablo de Olavide in Seville (Spain) is studying how industrialization processes and dietary changes have shaped the carbon footprint of Spanish agriculture between 1900 and 2008. This period covers the practical totality of its metabolic transition from solar-based traditional activity to fossil fuel-based industrial activity.

Spanish agriculture has experienced vast technological and structural changes in the twentieth century. Rapid industrialization in the second half of the century led to the extended use of fossil fuel-based inputs for mechanization, fertilization, irrigation and pest management, and in the last decades to the import of massive amounts of animal feed, much of it cultivated in deforested areas. These changes fed population growth, a rise in the share of animal products in the average diet, and an increase of high-value crop products for export. These historical changes deeply altered nutrient, material and energy fluxes, up to the present situation of high environmental pollution, energy and feed dependencies and low energy efficiency. [1] [2] [3] Today, GHG emissions from agriculture contribute approximately 11% of Spanish greenhouse gas emissions according to the National Emissions Inventory. [4] However, this figure only includes N₂O and CH₄ emissions, so the magnitude of the total carbon footprint and its evolution in response to the historical socio-ecological changes are unknown so far.

GHG diagram — Figue 1. Schematic representation of the main fluxes and processes considered for the estimation of the greenhouse gas emission balance of Spanish agroforestry sector

As part of the Sustainable Farm System (SFS) project, we estimate the evolution of the carbon footprint of Spanish agriculture from a life cycle assessment perspective, including all the relevant processes involved and adjusting emission factors to agro-climatic characteristics and temporal technological changes. The main fluxes studied are represented in a simplified way in Figure 1. First, we reconstruct the life cycle inventories of Spanish agriculture and livestock production, i.e., the main inputs and outputs of these activities, based mainly on historical sources and biomass partitioning coefficients. [5] Next, we estimate the evolution of greenhouse gas emissions associated to the industrial production of the major agricultural inputs, based mainly on the evolution of their embodied energy. [6] We then estimate field emissions of nitrous oxide and livestock emissions of trace gases following IPCC methodology and specific Mediterranean emission factors. [7] [8] Finally, we also estimate the carbon balance of the forest based on historical land use, harvest, wildfires and vegetation growth data. [9]

The preliminary results show drastic changes in the GHG emissions balance of the Spanish agroforestry sector that took place since 1900 (Figure 2). Emissions from traditional early twentieth century were dominated by enteric CH₄ emissions from ruminants (cows, sheep and goats) and field N₂O emissions (mainly from grazing). After the Spanish Civil War (1936-39) and the Autarchy period of Francisco Franco’s dictatorship in the 1940s and early 1950s, the Spanish agricultural sector experienced rapid industrialization that was reflected in the fast growth in GHG emissions. This growth was first dominated by fossil fuel-based inputs such as machinery fuel and fertilizers, and later by irrigation energy and specially by livestock-associated emissions,including manure management and feed imports (mainly land use change emissions from soybean cultivation in Latin America). In parallel, the stock of trees biomass grew, but the functionality of the forest decreased, as timber and pulp wood harvests did not compensate for the fall in firewood and grazing biomass, and the increase in wildfires losses.

Spanish GHG chart — Figure 2. Greenhouse gas emission balance of the Spanish agroforestry sector, 1900-2008 (Teragrams of CO2-equivalents)

Overall, the carbon footprint of Spanish agriculture increased six-fold, while per-capita emissions increased almost three-fold and emissions per kilocalorie produced roughly doubled. These changes, driven by the rising demand for animal products and increased waste of food products, took place despite substantial improvements in the efficiency of industrial inputs production and animal feed conversion ratios. Therefore, this preliminary analysis of historical GHG emissions in Spanish agriculture suggests that the significant productivity growth achieved by agricultural industrialization came with a much greater growth in environmental impacts, indicating that efficiency gains in specific processes could not offset structural changes associated to agroecosystem intensification and consumption patterns.

Notes

[1] García-Ruiz, R., Guzmán, G., Infante-Amate, J., Soto, D., Aguilera, E., Cid, A., Herrera, A., Gil, I., Molina, M.G.d., 2015. From shortage to wastage: soil fertility management in the socio-ecological transition of Spanish Agriculture, 1900-2010. Rural History 2015. European Rural History Organisation, Girona, Spain.

[2] Infante Amate, J., Soto Fernandez, D., Aguilera, E., García-Ruiz, R., Guzmán, G.I., Cid, A., González De Molina, M., 2015. The Spanish transition to industrial metabolism. Long-term material flow analysis (1860-2010). Journal of Industrial Ecology 19, 866-876.

[3] Lassaletta, L., Billen, G., Romero, E., Garnier, J., Aguilera, E., 2014. How changes in diet and trade patterns have shaped the N cycle at the national scale: Spain. Regional Environmental Change 14, 785-797.

[4] MAGRAMA, 2013. Inventario de emisiones de gases de efecto invernadero de España 1990-2011. Ministerio de Medio Ambiente, Medio Rural y Marino, Madrid.

[5] Guzmán, G.I., Aguilera, E., Soto Fernández, D., Cid, A., Infante-Amate, J., García-Ruiz, R., Herrera González de Molina, A., Villa Gil-Bermejo, I., González de Molina, M., 2014. Methodology and conversion factors to estimate the net primary productivity of historical and contemporary agroecosystems. Sociedad Española de Historia Agraria – Documentos de trabajo, DT-SEHA 1407. http://hdl.handle.net/10234/91670

[6] Aguilera, E., Guzmán, G.I., Infante-Amate, J., Soto, D., García-Ruiz, R., Herrera, A., Villa, I., Torremocha, E., Carranza, G., González de Molina, M., 2015. Embodied energy in agricultural inputs. Incorporating a historical perspective. Sociedad Española de Historia Agraria – Documentos de trabajo DT-SEHA 1507. http://hdl.handle.net/10234/141278

[7] IPCC, 2006. Guidelines for National Greenhouse Gas Inventories vol. 4. Agriculture, Forestry and Other Land Use. Intergovernmental Panel on Climate Change, Japan.

[8] Aguilera, E., Lassaletta, L., Sanz-Cobena, A., Garnier, J., Vallejo, A., 2013. The potential of organic fertilizers and water management to reduce N2O emissions in Mediterranean climate cropping systems. Agriculture, Ecosystems and Environment 164, 32-52.

[9] Infante-Amate, J., Soto Fernández, D., Iriarte-Goñi, I., Aguilera, E., Cid, A., Guzmán Casado, G.I., García-Ruiz, R., González de Molina, M., 2014. La producción de leña en España y sus implicaciones en la transición energética. Una serie a escala provincial (1900-2000). DT-AEHE. Asociación Española de Historia Económica.