PhD (M/F) entitled "Comprehensive assessment of land CDR fate of additional carbon, uncertainties, and feedbacks"

Job Description

Thesis Subject

Comprehensive assessment of land CDR
fate of additional carbon, uncertainties, and feedbacks

Terrestrial Carbon dioxide removal (mCDR) aims to offset anthropogenic CO₂ emissions either through engineered approaches or by enhancing natural biogeochemical processes. Nature-based solutions primarily rely on increasing net carbon uptake by terrestrial ecosystems, notably through afforestation, reforestation, and changes in forest and crop management. While such approaches are increasingly embedded in national mitigation strategies, large uncertainties remain regarding both their effectiveness and durability.
A central unresolved question concerns the fate of the additional carbon absorbed by terrestrial ecosystems, particularly forests: in which pools (biomass, litter, soils) is this carbon stored, over what timescales, and how vulnerable is it to climate variability, disturbances, and management choices? The long-term effectiveness of land-based CDR critically depends on the residence time of this additional carbon and on feedbacks with the climate system. Moreover, uncertainties in the representation of key processes—such as photosynthesis, carbon allocation, turnover, mortality, soil carbon dynamics, and disturbance regimes—limit confidence in current CDR estimates.

This PhD project aims to provide a comprehensive assessment of land-based CDR by quantifying where additional carbon is stored, how long it persists, and how robust these outcomes are to uncertainties in process representation and model parameters. The work will focus on land-use change and management practices in forests and crops, with particular attention to their interactions with climate change and Earth system feedbacks.
The project will rely on the land surface models SURFEX/ISBA and ORCHIDEE, which form the land components of the French Earth System Models CNRM-ESM and IPSL-CM, respectively. Recent developments in forest management in ORCHIDEE and irrigation in ISBA will be fully exploited. Uncertainty quantification will be addressed through systematic exploration of model parameter space and sensitivity analyses within these modelling frameworks.

Task 1 – Fate and efficiency of land CDR at the global scale
Objectives
• Quantify the efficiency of land-based CDR through land-use change and management in forests and crops.
• Track the fate of additional carbon across ecosystem pools (aboveground biomass, belowground biomass, litter, soil organic carbon) and assess associated residence times.
• Evaluate sensitivity to elevated atmospheric CO₂ and increasing disturbances (droughts, fires).
Methods
• Offline point-scale simulations with ISBA and ORCHIDEE on available stations offering either chronosequences of soil carbon stock and forest biomass (e.g, Boysen et al. 2021).
• Diagnose carbon allocation, turnover rates, and pool-specific storage times.
• Identify key processes controlling carbon permanence and vulnerability (and associated model parameters)

Task 2 – Uncertainty in process representation and parameter-space exploration
Objective
• Quantify uncertainties in land CDR storage efficiency and carbon permanence arising from model structure and parameter choices.
Methods
• Identify key uncertain processes and parameters controlling photosynthesis, carbon allocation, mortality, soil carbon turnover, and disturbance responses.
• Define physically and observationally plausible parameter ranges.
• Conduct structured sensitivity experiments and perturbed-parameter ensembles within ISBA and ORCHIDEE.
• Bracket uncertainty in total carbon uptake, pool partitioning, and persistence timescales, including defining alternative configurations with optimistic and pessimistic set of parameters for what-if experimental set-up.

Task 3 – Resilience of land carbon sinks and Earth system feedbacks
Objective
• Assess the resilience of land carbon sinks under climate change and identify feedbacks associated with land-based CDR.
Methods
• Perform fully coupled Earth System Model simulations using the set of parameters selected from Task 2 (upscaling hypothesis) using the best, the optimistic and the pessimistic sets of parameters
• Evaluate side effects of CDR on the water cycle, energy balance, and biogeophysical feedbacks.
• Focus on forest vulnerability to drought and fire, and on water-cycle impacts of crop management and irrigation.
• Assess reversibility and risks of carbon loss under extreme events.

Task 4 Interaction between mCDR and other climate intervention method
Objective: How CDR (land and marine) methods can be influenced by other climate intervention such as SAI (stratospherical aerosol injection).
Method: Collaboration within the GEOSIC project to explore

Your Work Environment

The PhD position will be hosted at CNRM (Toulouse, France) and funded through the GEOSIC project, which aims to improve our understanding of the interactions between CO₂ removal methods, Earth system feedbacks, and other climate intervention approaches. This research framework will provide the PhD candidate with a multidisciplinary scientific environment at the interface of Earth system modelling, the carbon cycle, land-use change, and the assessment of climate change mitigation strategies.

Constraints and risks

None

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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