This challenge will study land-based mitigation of climate change by enhancing carbon sequestration in biomass and soils, and reducing their CH4 and N2O emissions. We will investigate the contributions of and interactions between technology-driven and ‘nature-based’ solutions (leading to new food production systems) through which LUM can mitigate climate change over different time horizons, their economic feasibility, and indirect environmental consequences. At the international level, this work will contribute to climate assessments including IPCC‘s upcoming special reports on the 1.5°C climate targets and to the IPBES assessment.


Research line 1.1: Reducing GHG emissions in the land-use sector, in support of the Paris agreement

In the first phase, the teams will review the Intended Nationally Determined Contributions reported to the UNFCCC before the COP21 (INDCs to become NDCs) for the LUM sector in different countries and calculate their impact on GHG emissions, radiative forcing, and climate change for the horizon 2030-2035. In the second phase, the LUM component of the new (NDCs will be updated every 5 year as per the Paris Agreement) will be analyzed in terms of economic costs and socioeconomic implications and compared with mitigation in other sectors. In the last phase, the analysis will be extended to include ecological feedbacks, and connected to the long-term scenarios of RL 1.2.


Research line 1.2: Impact of land-based carbon dioxide removal on climate and the environment

This research line will investigate the impacts of large-scale deployment of land-based carbon dioxide removal (CDR including BECCS) technologies causing the ‘negative emissions’ assumed in most low warming IPCC scenarios for the next century (1.5°C to 3.5°C Shared Socioeconomic Pathways, or SSPs). In the first phase, the potential of CDR technologies will be benchmarked against the wealth of readily available data on carbon sequestration and ecosystem primary productivity collected by the teams (e.g. forest management, afforestation, increased soil carbon storage). In the second phase, building on the storylines of the SSP scenarios, we will attempt to estimate the poorly known environmental impacts and climate feedbacks of future CDR technologies, in particular BECCS. These impacts concern water and nutrient demands and limitations (HBAN, GEOPS, AGRONOMIE), air quality (emissions of pollutants by soils; ECOSYS, LATMOS, BIOGER), as well as soil fertility changes (AGRONOMIE, ECOSYS, SADAPT) and biodiversity. In the third phase, the full GHG balance effects including CO2, N2O and CH4 fluxes, and important biophysical climate feedback loops from land based CDR (e.g., altered surface albedo from large scale BECCS production) will be assessed for SSP scenarios, using the IPSL Earth System Model, thus meeting the first frontier science priority proposed in the scientific vision (1.1). Plausible environmental costs will be incorporated into the Integrated Assessment Model of CIRED (Waisman et al. 2012).


Research line 1.3: Consistent scenarios for the role of agriculture and managed forests in climate mitigation

In this research line, the teams will work together to better quantify the full climate mitigation potential of LUM (crop and livestock production, forestry). In the first phase, the consistency between IPCC SSP scenarios, IPBES scenarios, and OECD Representative Agricultural Pathways (RAPs) will be analyzed for future changes in LUM. The resulting GHG emission trajectories (and their uncertainties) will be estimated using ecosystem models at regional scale (mainly for France, the EU, and for Africa and China with collaborations) and at global scale. In the second phase, based on the synthesis of published results of low-GHG agricultural and forestry practices and field data, we will produce alternative pathways of more efficient land-based GHG mitigation, that will be incorporated in the LUM socioeconomic models of ECOPUB (Europe) and CIRED (global). The cost-competitiveness of land-based measures will be evaluated and their price, land use and international trade impacts quantified. In the third step, the teams will quantify the implications of the above LUM mitigation scenarios for irrigation water (HBAN), fertilizer use (AGRONOMIE, ECOSYS), biodiversity (IDEEV, CIRED), and the climate feedbacks from altered biophysical land properties (LMD, LSCE) using the CLAND-CMP platform, a frontier research topic proposed in Sect. 1.1.