Reference ecological states for contextualization

Large-scale agriculture is linked to a shift from natural to anthropogenic emissions. Despite the agrifood system being assumed as an activity that starts emitting GHGs from a zero baseline, the current quantification of their net climate impact neglects the warming associated with baseline conditions (reference ecosystems), such as those before agricultural establishment, thus failing to consider the carbon (C) balance status before land use change [3]. Broadly speaking, neglected mechanisms related with land use/land use change are the natural C and reactive nitrogen (N) emitters, such as herbivores and wetlands, albedo shapers (determined primarily by land cover) or disturbances in C sequestration (e.g., wildfires). As a proof of concept, the importance of considering these natural baseline conditions was recently demonstrated in East Africa. A reference ecosystem (Serengeti National Park) was compared with the adjacent Loliondo Game Controlled Area, analogous in functional terms yet managed through low-input pastoralism by local Maasai people, resulting in both areas showing similar megaherbivore biomass and GHG emissions [4]. This suggests that, at least in some areas of the world, natural GHG emissions have always been significant, and abandoning grazing livestock activity may not necessarily lead to a net GHG reduction.

The main challenge for these counterfactual scenarios is defining the reference ecosystem or biome that land use would move towards, if abandoned, rewilded, or restored (except in hysteresis situations; e.g., desertification). While some tropical biomes have reference primary ecosystems (forests or savannas), there is still much discussion and debate about other areas where the ecological reference is subjected to interpretation after thousands of years of human interference [5], leading to the so called “Uncertain Ecosystems” [6]. In this sense, Pauné [7] has shown how large forested areas of the Mediterranean are pastoral ecosystems impoverished by a lack of herbivory and partially extinct biocenosis, where large fires perpetuate the system. Assuming one reference status over another has significant effects on net warming associated with land use (such as net GHG emissions, C sinks and albedo).

Measurement according to subsectors and site conditions

There have been some attempts to integrate the reference ecological states into existing methodologies (e.g., classical attributional and consequential LCA) to capture the overall implications of the agrifood system transition into climate change, although some limitations exist. Pardo et al. [8] proposed to include estimated local natural emissions into the ecosphere in some pastoral systems, resulting in a substantial reduction of the carbon footprint of the subsequent food products. For albedo changes, the International Reference Center for Life Cycle Assessment and Sustainable Transition (CIRAIG) has recently calculated global characterization factors of warming associated with albedo (in kg CO₂e/m 2/yr) for different land uses, reporting that impacts of agricultural land use would be largely equivalent to negative emissions in many cases.

Beyond the non-inclusion of reference state limitations, the methodologies for quantifying GHG emissions from livestock are subject to large uncertainties when applied in extensive livestock systems, specially for low- and middle-income countries (e.g., in Africa: [9]).

All these caveats, which are particularly and inherently linked to different types of food production systems, need to be incorporated into debates around food sustainability, whether in policy instrumentation (e.g., the EU Common Agricultural Policy) or in connection with evidence-based information for consumers. For instance, current metrics used for climate impact, like the carbon footprint, tend to focus on foods with high methane intensity (e.g., ruminants and rice), while ignoring other critical aspects mentioned above. This can lead to strategies with strong messages advocating for heavy reductions in rice consumption or transitioning from grazing ruminant-based livestock systems to “sustainably” intensified and generally landless monogastric-based livestock systems.

For whom and from whom? Socio-ecological features

Additionally, there is a growing recognition of the importance of assessing agrifood systems within cultural and socio-economic contexts. The latter comes from the necessity to translate the land use impacts and GHGs quantification into successful policies, as there are complex systems shaping food production, dietary patterns, and activities along the entire food chain. Given the diverse contexts of households, food chain actors, and food environments, research and policy must account for these complexities [10]. This is relevant since decisions about what we eat lead to changes in land use, with implications in vegetation structure, affecting C stocks, wildfires and albedo.

For example, during the last cenutry Spain moved from multifunctional extensive farming towards industrialized livestock and from the 1960s to an increase of meat (pork and broiler), milk and eggs consumption and a processed food industry. Such landscape changes, e.g., an increase in cropland expansion, has led to lower Soil Organic C levels and an increase in C and N footprint [11] and wildfire severity [12] and C release. In parallel, a cultural disconnection between city and country in a market economy framework has reduced the options for local or traditional consumption, deeply affecting changes in landscape, rural economy, health and nutrient cycles (emissions).

The oversimplification of messages around this, added to the globalization of diets around the world, are causing a decline in traditional and Indigenous agrifood systems. In low-income regions such as Sub-Saharan Africa, these traditional food systems have been vital for improving nutrition and food security [13]. At the same time, globalization and industrialization in mid- and high-income countries have resulted in increased consumption of ultra-processed foods high in fat and sugar and animal-based proteins [14]. These trends generate different degrees of affordability for healthy and sustainable diets [15]. Moreover, the High Level Panel of Experts on Food Security and Nutrition highlights how these disparities are also observed within countries, where socio-economic status significantly influences the choices of consumers. However, consumers’ choices are limited by the food supply within the food environment.

In summary, given the variations in contexts across regions and countries, both research and political decisions for food sustainability assessment models should be tailored to reflect these differences alongside the agrifood network and site-based baselines. This approach is necessary to identify potential opportunities for reducing impacts and informing policy decisions. For instance, at the production level, enhancing productions linked with the territories needs to be taken into account. At the retail and consumption levels, information related to typologies of production can enhance accountability for both retailers and consumers. Finally, special attention is needed when examining the consumption side of agrifood systems, particularly regarding socioeconomic disparities and vulnerable hotspots.