Leakage of nitrous oxide emissions within the Spanish agro-food system in 1961–2009

Abstract

In this paper we examine the trends of nitrous oxide (N₂O) emissions of the Spanish agricultural sector related to national production and consumption in the 1961–2009 period. The comparison between production- and consumption-based emissions at the national level provides a complete overview of the actual impact resulting from the dietary choices of a given country and allows the evaluation of potential emission leakages. On average, 1.5 % of the new reactive nitrogen that enters Spain every year is emitted as N₂O. Production- and consumption-based emissions have both significantly increased in the period studied and nowadays consumption-based emissions are 45 % higher than production-based emissions. A large proportion of the net N₂O emissions associated with imported agricultural goods comes from countries that are not committers for the United Nations Framework Convention on Climate Change Kyoto Protocol Annex I. An increase in feed consumption is the main driver of the changes observed, leading to a remarkable emission leakage in the Spanish agricultural sector. The complementary approach used here is essential to achieve an effective mitigation of Spanish greenhouse gas emissions.

Appendix: Technical notes about the emission factors

The N₂O EFs for most of the studied crop products were calculated as averages of the values provided in the LCA databases USDA, LCA Food DK and Ecoinvent (USDA 1998; Nielsen et al. 2003; Ecoinvent Centre 2007,), implemented in SimaPro 7. These products are wheat, rice (Oryza sativa), barley, maize, rye (Secale cereale), oats (Avena sativa), sorghum (Sorghum sp.), other cereals, potatoes, sugar cane (Saccharum officinarum), sugar beets (Beta vulgaris), pulses, sunflower (Helianthus annuus) seed, rape (Brassica napus) and mustard (Sinapis sp.) seed, cotton (Gossypium sp.) seed, other oil crops, tomatoes (Solanum lycopersicum), other vegetables and other fruits. World median EF values from Nemecek et al. (2011) were used for treenuts, groundnuts (Arachis hypogaea), palm kernels (Elaeis guineensis), onions (Allium cepa), oranges (Citrus x sinensis) and mandarins (Citrus reticulate), bananas and platains (Musa x paradisiaca) and apples (Malus domestica). Data from Audsley et al. (2009) was used for estimating the EFs of tea (Camelia sinensis), pepper (Piper nigrum), pimento (Capsicum annuum), cloves (Syzigium aromaticum) and other spices. Coffee (Coffea sp.) EF was taken from Hergoualc’h et al. (2007). When we did not find specific EFs, we used the EF of a similar crop. Particularly, sorghum EF was used for millet (Panicum miliaceum); potato EF for cassava (Manihot sculenta), sweet potatoes (Ipomoea batatas) and other roots; pulses average EF for beans and other pulses; oilcrops average EF for coconuts (Cocos nucifera) (incl. copra); sunflower and rapeseed average EF for sesame (Sesamum indicum) seed; oranges EF for lemons (Citrus x limon), limes (Citrus x aurantifolia), grapefruit (Citrus x paradise) and other citrus; coffee EF for cocoa (Theobroma cacao) beans; and banana EF for pineapples (Ananas comosus) and dates (Phoenix dactylifera).

Given the uncertainty in LCA-based EFs of soybeans, and the importance of this crop in Spanish international trade, an empirically-based EF of 1.253 g N-N₂O/kg product was calculated using world average emission data from Jensen et al. (2012) and yield data from FAOStat. The EFs of grapes, olives and forages were 0.058, 0.189 and 0.201 g N-N₂O/kg product, respectively, and they were estimated using Spanish data, as described in the methods section.

The EFs of the processed products were calculated from EFs of primary products using processing ratios obtained from Ecoinvent (Ecoinvent Centre 2007), FAOSTAT, and from own estimations (Table 3). Economic allocation was used to divide the N₂O emissions between the co-products. All meat values refer to carcass weight. Poultry meat EF was assumed for other meat. Butter and cream were assumed to have 80 % and 18 % fat contents, respectively. Allocation of emissions from the incoming milk to dairy products was done using dry mass as a suitable proxy for economic value. Milk category refers to raw milk assuming 4 % fat content (Table 4).

Herein we present an example of the calculation of N₂O emissions associated with animal products. As we indicate in the methodology section, the calculation of N₂O emissions associated with animal products requires particular attention. We considered different EFs for production, imports and exports, in order to reflect differences between Spanish and foreign production systems, and to avoid double counting of emissions involved in other sections of the study. All these calculations require a last correction for meat because production data include not only national production (indigenous meat), but also those animals imported alive that are slaughtered in Spain. Herein we present the example of the calculations for bovine meat N₂O emissions (Tables 5, 6, 7 and 8).

For products produced in Spain we only took into account N₂O emissions associated with manure management and direct excretion of grazing animals because other emissions have been already accounted in the crops and processed products calculations. For imported products we used a complete EF that includes also feed production. This EF is general and not specific to any country. For exported cattle meat we used a complete EF (i.e., including feed production) specific for Spain. For imported as live animals we used same EF as for imported cattle meat. For exported as live animals only feed production is considered (9.13 g N-N₂O/kg product; Leip et al. 2010). Finally, we correct the emission taking into account the live animals: To the final account we remove imported as live animals to the production and we add this to the import value. We also add exported as live animals emissions to the export emissions.

Table 3 Weight of primary matter per kg of processed product and proportion of the N₂O emissions allocated to the co-products

Table 4 Emission factors used for the animal production

Table 5 Production and trade of bovine meat in 2009 in Spain

Table 6 Emission factors for cattle

Table 7 Results of the production multiplied by the EF

Table 8 Emission of N-N₂O associated to production, import and export of cattle meat in 2009