CHALLENGE 1 - LAND-BASED CLIMATE MITIGATION

This challenge mainly aims at evaluating the land-based climate mitigation options on different aspects (climate, green houses gases emissions, economical costs, etc.) and how these land-based mitigation options are integrated into National Determined Contributions (NDCs). The challenge one is divided into three research lines which are divided into different work packages. Research lines are strongly embedded with important interactions between all the work packages. The details on the research lines are provided below.

Research line 1.1: Review and design of global and regional land-based mitigation scenarios

The plan of this research line is to first review the different types of land-based mitigation measures (LMM) currently incorporated in future climate scenarios by integrated assessment models under different climate warming objectives (SSPs-RCPs). The specific LMMs that will be reviewed are biofuels associated with CO2 capture and sequestration known as BECCS, afforestation and reforestation, soil carbon storage, reduction of N2O and of CH4 emissions including the scale of deployment in each region, the timing of deployment and assumed costs in integrated assessment models. Then a meta-analysis of the current BECCS yields in different regions and for different levels of fertilization / irrigation inputs will be performed. Finally, the abatement potential, cost and potential applicability of land-based mitigation will be calculated with a detailed socio-economic model for France with regional details building up upon previous national projects.

Research line 1.2: Multi-criteria assessment of selected land-based mitigation measures

This research line will focus on the environmental and ecological impacts of developing land-based mitigation, while the efficiency and GHG abatement potentials of candidate LMM measures are addressed in RL1.1. Most of the literature on LMM focuses on the latter aspects while their impacts other than GHG emissions are often only qualitatively addressed although they are likely to be significant when LMM are deployed at a relevant scale. Limitations imposed by natural resources, e.g. the availability of water and nutrients to grow biomass and of N to bind with increasing soil organic C pools or water to grow biomass feedstock for BECCS is also acknowledged but still debated for lack of an adequate evaluation framework. Other constraints may be positive or negative effects on ecosystem services provided by agroecosystems and forests (e.g. biodiversity habitat, erosion control, water quality and quantity regulation). Research Line 1.2 will review the state-of-the-art on the main impacts of LMM and the methodology available to assess them through an international workshop supplemented by adhoc meta-analyses and simulation work. This will provide insight into the potential impacts of large- scale LMM deployment scenarios in two contrasting socio-economic and biophysical contexts.

Research line 1.3: Evaluation of NDCs in the AFOLU and agriculture sector and their mitigation potential

At COP21, 128 countries proposed a land use and management (LUM) section in their INDC, concerning both mitigation and adaptation. The associated measures make up circa 25% of the total GHG emissions reductions. NDCs are not very detailed at the moment (depending upon countries) about the LMMs that will be used to reach proposed targets and they also differ in their structure. In general, the AFOLU sector concerning forests and land use is part of many NDCs, whereas the agricultural sector is not the focus of NDCs because of potential food security tradeoffs of agricultural LMMs. This RL will provide a thorough analysis of the NDCs for the AFOLU sector and compare them with national plans and targets. The potential contribution of agriculture will be estimated based on the reports / plans of some countries for this sector (e.g. the French government objective to cut agricultural emissions by 20% of the 1990 values by the year 2026), encompassing their economic, social and environmental impacts, as well as propose a re-appraisal of their mitigation potential based on the findings of RL1.2. We propose to review the Nationally Determined Contributions reported to the UNFCCC at the COP21 for the LUM sector in different countries and calculate their impact on GHG emissions, radiative forcing, and climate change for the horizon 2030-2035. Then, a re-appraisal of selected NDCs will be proposed to emphasize the key measures or uncertainties of the LUM sector in various national contexts with a particular focus on soil carbon sequestration.

The activities of young CLand researchers within Challenge 1 on Land-based climate mitigation are currently continuing through:

• The work of Thais Diniz Oliveira on interactions within the Integrated Assessment Models (IAM).
• The completion of Yang Su's meta-analysis work on the impact of conservation agriculture on yields on a global scale.
• The work of Elisa Bruni published this year concerning the estimation of the carbon inputs necessary to reach the 4 ‰ objective.
• The study carried out by postdoctoral researcher Yuanyuan Huang on N2O emissions and their intensity in relation to fertilizer inputs.
• The writing of a literature review "Large scale deployment of soil C sequestration to mitigate climate change" following the workshop organized at the end of 2018 in Paris.