Search

International audience; Mineral nitrogen (N) application in agriculture has significantly increased food production over the past century. However, the intensive use of N-fertilizers also impacts negatively the environment, notably through greenhouse gas emissions and biodiversity loss and remains a major challenge for policymakers. In this paper, we explore the effects of a public policy aiming at halving agricultural mineral nitrogen use across the European Union (EU). We investigate the impacts on food security, climate mitigation, and biodiversity conservation and we analyse the potential trade-offs and synergies between them. Despite the uncertainties associated with monetary valuation and the choice of modeling approach, our results show that climate-and-biodiversity-related benefits of halving N use in EU agriculture more than offset the decrease in agricultural benefits.; L'application d'azote minéral (N) dans l'agriculture a considérablement augmenté la production alimentaire au cours du siècle dernier et a joué un rôle important dans la sécurité alimentaire mondiale. Cependant, l'utilisation intensive des engrais azotés a également un impact négatif sur l'environnement, notamment à travers les émissions de gaz à effet de serre et la perte de biodiversité, et reste un défi majeur pour les décideurs. Dans cet article, nous explorons les effets d'une politique publique visant à réduire de moitié l'utilisation d'azote minéral agricole dans l'Union européenne (UE). Nous étudions les impacts sur la sécurité alimentaire, l'atténuation du changement climatique et la conservation de la biodiversité et nous analysons les compromis potentiels et les synergies entre eux. Malgré les incertitudes associées à l'évaluation monétaire et au choix de l'approche de modélisation, nos résultats montrent que les avantages de la réduction de moitié de l'utilisation de N dans l'agriculture de l'UE, liés l'atténuation du changement climatique et à la conservation de la biodiversité, compensent largement la baisse des bénéfices agricoles.

Methane is a short-lived greenhouse gas (GHG) modelled distinctly from long-lived GHGs such as carbon dioxide and nitrous oxide to establish global emission budgets for climate stabilisation. The Paris Agreement requires a 24–47% reduction in global biogenic methane emissions by 2050. Separate treatment of methane in national climate policies will necessitate consideration of how global emission budgets compatible with climate stabilisation can be downscaled to national targets, but implications of different downscaling rules for national food production and climate neutrality objectives are poorly understood. This study addresses that knowledge gap by examining four methods to determine national methane quotas, and two methods of GHG aggregation (GWP100 and GWP*) across four countries with contrasting agriculture, forestry and other land use (AFOLU) sectors and socio-economic contexts (Brazil, France, India and Ireland). Implications for production of methane-intensive food (milk, meat, eggs and rice) in 2050 and national AFOLU climate neutrality targets are explored. It is assumed that methane quotas are always filled by food production where sufficient land is available. Global methane budgets for 1.5 °C scenarios are downscaled to national quotas based on: grand-parenting (equal percentage reductions across countries); equity (equal per capita emissions); ability (emission reductions proportionate to GDP); animal protein security (emissions proportionate to animal protein production in 2010). The choice of allocation method changes national methane quotas by a factor of between 1.7 (India) and 6.7 (Ireland). Despite projected reductions in emission-intensities, livestock production would need to decrease across all countries except India to comply with quotas under all but the most optimistic sustainable intensification scenarios. The extent of potential afforestation on land spared from livestock production is decisive in achieving climate neutrality. Brazil and Ireland could maintain some degree of milk and beef export whilst achieving territorial climate neutrality, but scenarios that comply with climate neutrality in India produce only circa 30% of national calorie and protein requirements via rice and livestock. The downscaling of global methane budgets into national policy targets in an equitable and internationally acceptable manner will require simultaneous consideration of the interconnected priorities of food security and (land banks available for) carbon offsetting.

The Paris Agreement commits 197 countries to achieve climate stabilisation at a global average surface temperature less than 2 °C above pre-industrial times, using nationally determined contributions (NDCs) to demonstrate progress vis-à-vis this goal. Numerous industrialised economies have targets to achieve territorial climate neutrality by 2050, primarily in the form of “net zero” greenhouse gas (GHG) emissions. However, particular uncertainty remains over the role of countries’ agriculture, forestry and land use (AFOLU) sectors for numerous reasons, inter alia: the need to balance mitigation of difficult-to-abate agricultural emissions against food security; agriculture emissions of methane do not need to be reduced to zero to achieve climate stabilisation; land use should be a large net sink globally to offset residual emissions. These issues are represented at a coarse level in integrated assessment models (IAMS) that indicate the role of AFOLU in global pathways towards climate stabilisation. However, there is an urgent need to determine appropriate AFOLU management strategies at national level within NDCs. Here, we present a new model designed to evaluate detailed AFOLU scenarios at national scale, using the example of Ireland where 34 % of national GHG emissions originate from AFOLU. GOBLIN (General Overview for a Back-casting approach of Livestock Intensification) is designed to run randomised scenarios of agricultural activities and land use combinations in 2050 within biophysical constraints (e.g. available land area, livestock productivities, fertiliser-driven grass yields and forest growth rates). Based on AFOLU emission factors used for national GHG inventory reporting, GOBLIN then calculates annual GHG emissions out to 2050 for each scenario. The long-term dynamics of forestry are represented up to 2120, so that scenarios can also be evaluated against the Paris Agreement commitment to achieve a balance between emissions and removals over the second half of this century. We outline the rationale and methodology behind the development of this biophysical model intended to provide robust evidence on the biophysical linkages across food production, GHG emissions and carbon sinks at national level. We then demonstrate how GOBLIN can be applied to evaluate different scenarios in relation to a few possible simple definitions of “climate neutrality”, discussing opportunities and limitations.

World agriculture needs to find the right balance to cope with the trilemma between feeding a growing population, reducing its impact on biodiversity and minimizing greenhouse gas (GHG) emissions. In this paper, we evaluate a broad range of scenarios that achieve 4.3 GtCO2,eq/year GHG mitigation in the Agriculture, Forestry and Other Land-Use (AFOLU) sector by 2100. Scenarios include varying mixes of three GHG mitigation policies: second-generation biofuel production, dietary change and reforestation of pasture. We find that focusing mitigation on a single policy can lead to positive results for a single indicator of food security or biodiversity conservation, but with significant negative side effects on others. A balanced portfolio of all three mitigation policies, while not optimal for any single criterion, minimizes trade-offs by avoiding large negative effects on food security and biodiversity conservation. At the regional scale, the trade-off seen globally between biodiversity and food security is nuanced by different regional contexts.

The increased use of legumes is viewed as a promising option to mitigate climate change, as they are a source of proteins and provide nitrogen to the soil. In this paper, we evaluate a strategy for the increased use of legumes in Europe until 2050 by integrating a large array of food and natural system processes into a consistent modeling framework. Three contrasting scenarios are studied: a supply-side scenario entailing a change in the animal feed mix, a demand-side scenario entailing a shift in human diet, and a combination of the shift in human diet with a reforestation in Europe. We find that mitigated emissions are much higher in the two diet shift scenarios (-231 and -259 MtCO2eq, respectively) than in the supply-side scenario (-10 MtCO2eq). Therefore, the main environmental benefit of legumes is to provide proteins as a substitute for animal products rather than enabling a lower consumption of synthetic fertilizer through increased leguminous nitrogen fixation. Diet shift scenarios require a lower use of lands that can then be used to either reduce intensification or reforest. In the former case, the reduction in emissions concerns almost exclusively non-CO2 emissions, mainly through enteric fermentation and manure management, and occurs largely outside Europe. In the latter case, the livestock sector still represents a substantial share of the emission reduction but is outpaced by CO2 emissions through carbon sequestration. An increase in legume production substantially reduces greenhouse gas emissions from the AFOLU sector only when combined with a change in diet, and its combination with reforestation allows the emission reduction to be relocated to Europe through carbon sequestration. Our study concludes that an increase in legume production accompanied by appropriate measures on both the supply and demand side can be effective in reducing emissions. These results can be used to design the European Commission’s “Farm to Fork” strategy for sustainable food and to support climate-friendly farming practices of the post-2020 European common agricultural policy.

International audience; Hypertelescopes are large optical interferometric arrays, employing many small mirrors and a miniature pupildensifier before the focal camera, expected to produce direct images of celestial sources at high resolution. Their peculiar imaging properties, initially explored through analytical derivations, had been verified with simulations before testing a full-size testbed instrument. We describe several architectures and optical design solutions and present recent progress made on the Ubaye hypertelescope experiment. Arecibo-like versions with a fixed spherical primary meta-mirror, or an active aspheric one, have a suspended focal beam combiner equipped for pupil-drift accommodation, with a field-mosaic arrangement for observing multiple sources such as exoplanetary systems, globular clusters or active galactic nuclei. We have developed a cable suspension and drive system with tracking accuracy reaching a millimeter at 100m above ground.