PhD thesis : Impacts of geoengineering through stratospheric aerosol injections on atmospheric dynamics and detectability in idealised and geopolitically constrained scenarios (M/F)

Job Description

Thesis Subject

This PhD thesis, funded by the ANR (PEPR TRACCS, GEOSIC project), aims to study the impact of solar geoengineering on atmospheric dynamics. Solar geoengineering (SRM) encompasses proposed methods for mitigating some of the impacts of climate change, but it does not address the underlying causes. SRM is primarily studied using climate modelling, and the feasibility of its deployment remains uncertain. Nevertheless, it has now also entered political discussions, raising questions that will need to be answered with scientific knowledge. The stratospheric aerosol injection (SAI) method aims to strengthen the stratospheric aerosol layer, for example by injecting gaseous SO2 into the stratosphere, which then transforms into sulphate aerosols. Variations in this aerosol layer can alter the stratospheric thermal structure and circulation, having dynamic impacts on a global scale. These impacts may manifest as changes in the QBO, the monsoon, the NAO and the polar vortex, for example.
This PhD project will use the IPSL coupled climate model (IPSL-CM) to study and analyse the potential impact of the SAI on atmospheric dynamics and the detectability of SAI deployment. The IPSL-CM contains a stratospheric aerosol microphysics module. It has recently been coupled with a 'controller' that allows the simulation of actors deploying the SAI by optimising injections to achieve a specific climate objective: for example, global temperature, precipitation in the Northern Hemisphere, and so on. In particular, the project involves integrating deployment scenarios developed with constraints from the humanities and social sciences (law, governance, security) into climate modelling, and assessing the impact of such SAI scenarios on the climate system. These scenarios will be implemented in the simulations via the controller mentioned above.
The thesis involves climate modelling using the IPSL-CM model, employing 'standard' SAI scenarios, such as those used in the GeoMIP model intercomparison project, and SAI scenarios developed as part of the GEOSIC project, as well as analysing the results to quantify the sources of changes in various dynamic phenomena. An observation simulator (e.g. lidar) will be set up to study the detectability of very weak initial emissions, identify detection thresholds for current instruments and assess requirements for future instruments.
The PhD student will learn to use the IPSL climate model, IPSL-CM, and carry out the necessary simulations, including controller calibration simulations. CMIP6 GeoMIP simulations will also be available to perform initial dynamic analyses whilst awaiting the new simulations. The PhD student will use and develop Python scripts for analysing results and may participate in the development of codes such as the observation simulator and the improvement of the controller.
The proposed thesis will investigate the impacts of SAI deployment through the analysis of modelling experiments, either based on GeoMIP simulations or by conducting various experiments on ad hoc scenarios developed by researchers in the GEOSIC project, based on research in geopolitics. We will implement the scenarios developed for the SAI deployment in a climate model coupled with a control module (PID) in order to quantitatively simulate possible governance systems and assess their level of resilience. The control module has already been coupled with a simplified climate model that was used to test non-coordinated deployment scenarios by two actors (Boucher et al. 2024, Määttänen et al. 2026). In 2025, the control module was coupled with the IPSL climate model (Boucher et al. 2020) to enable the simulation of SAI deployment by multiple actors with different climate objectives using a coupled climate model. The scenarios used involve actors who may or may not communicate/agree on actions and may or may not have common objectives, based on the governance scenarios derived from GEOSIC.
The PhD thesis will draw on two sets of simulations: 1) the standardised GeoMIP experiments carried out during CMIP6 and for the CMIP7 Fast Track using the IPSL model, and 2) the ad hoc experiments designed during the GEOSIC project (including a series of simulations to calibrate the controller parameters). The availability of GeoMIP simulations allows the PhD student to begin and develop the analysis of atmospheric dynamics, but they will also carry out new simulations on geopolitically relevant experiments during the project.
The analysis will first document how general circulation phenomena (jets, temperature and precipitation distributions) are affected by SAI and vary according to different SAI strategies. Substantial variations are indeed expected (e.g., Bednarz et al. 2023). Subsequently, the study will focus on quantifying and understanding the impacts on stratospheric overturning circulation (Brewer-Dobson circulation) and the quasi-biennial oscillation of tropical stratospheric winds. The LMDZ is one of the few global climate models (GCMs) to feature a realistic QBO and stratospheric circulation in the current climate, which allows these effects to be studied. The impacts of potential 'termination shocks' in the simulations will be studied in detail.
A detailed analysis of the momentum balance in the simulations using the transformed Eulerian mean (Andrews et al., 1989) will be carried out to assess the various contributions to changes in circulation, in particular to disentangle the direct effects of the modified radiation balance and the structure of the heating rate on updrafts and downdrafts and the associated vertical momentum advection, from indirect feedbacks due to changes in the propagation or excitation of large-scale Rossby waves. This improved understanding will provide us with a conceptual model of the stratosphere's circulation response to the SAI. The QBO has multiple teleconnections with the NAO, the state of the polar vortex and tropospheric convection, and this analysis will lead to a better understanding of the changes in general circulation caused by the SAI.
The thesis will also address the issue of the detectability of SAI deployment in various scenarios, thereby contributing to the GEOSIC project's research priorities regarding the geopolitical tensions that SAI deployment could provoke. To this end, we will implement two satellite instrument simulators: a space lidar simulator and a limb sounder simulator, using dedicated radiative transfer simulations corresponding to existing or proposed instruments. The virtual measurements will be compared with expected noise levels and observed natural variability.
Finally, this thesis will contribute to the final stages of the GEOSIC project by analysing the results of SAI deployment scenarios to study (by dedicated staff) their impacts on national security in France (defence, agriculture, water resources, etc.).
The candidate should have a background in physics, particularly atmospheric physics or a similar field, and experience in modelling and programming. The ability to work independently and as part of a team is expected, as well as good organisational skills and scientific writing abilities. Familiarity with Linux/Unix is an advantage.

Your Work Environment

The PhD is funded by the ANR through the PEPR TRACCS programme as part of the GEOSIC project (Geopolitics and Science of Interventions on the Climate).
The PhD student will be based at LATMOS in Jussieu and will be co-supervised by LATMOS (A. Määttänen) and LMD (A. Podglajen), and will work within a team of researchers specialising in atmospheric physics and research engineers with expertise in modelling, whilst interacting with a wider, interdisciplinary team within the GEOSIC project.
Collaborations within the GEOSIC project are foreseen, with a postdoc in international law who will lead the development of SAI deployment scenarios and the team working with them, and with the project's wider modelling group. Within IPSL, collaboration is envisaged with P. Sellitto's team (LISA) on SAI detectability. Further collaborations are envisaged within the GeoMIP community with international modelling groups to contribute to discussions on atmospheric dynamics during SAI deployment.
The research and findings will be published in peer-reviewed scientific journals and presented at international conferences. Presentations at meetings and webinars organised by the GEOSIC project and the PEPR TRACCS programme are also planned. The principles of open science will be applied (open-access publication).
The international connections of the PhD project will be ensured through presentations at international conferences and publications in scientific journals. The PhD student's participation in events organised by international networks such as GeoMIP will be encouraged by the supervisors. Any other opportunities, such as short research visits or the establishment of new collaborations, will be pursued where possible.
The PhD student will have access to a laptop, the IT infrastructures of LATMOS and the IPSL (ESPRI mesocentre) and the national supercomputing centres where the climate simulations will be carried out (such as the CEA's TGCC). The GEOSIC project includes funding for travel and other expenses during the thesis.
A background check of the candidate by the Security and Defence Officer is mandatory.
Interviews for shortlisted candidates are likely to take place on 22 April (morning).

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

The research professions