Some vegetation ecosystems could reach a tipping point -a threshold beyond which the climate could be abruptly and permanently affected- including the Sahara and the boreal forests (Armstrong McKay et al., 2022). The aridification of the Sahara and the southward shift of the boreal forests during the Holocene have been successfully reproduced with the IPSL Earth System Model including dynamical vegetation, highlighting the abrupt end of the African Humid Period as well as multi-decadal variability in the high northern latitudes. However, only natural vegetation has been considered, without accounting for its replacement by land use expansion in certain regions (Braconnot et al., 2025). Since vegetation changes affect radiative fluxes and the water cycle, taking land use into account could impact the feedbacks that regulate long-term climate and potentially influence the occurrence of tipping points.

In this context, the objectives of the internship are:
1) to assess the impact of land use on regional climate and identify how it affects aridification;
2) to determine how much these feedbacks depend on the background climate-vegetation state.

The starting point will be to isolate the feedbacks in simulations with and without land use, and with either dynamical or prescribed vegetation representing the mid-Holocene and pre-industrial periods. Adapted statistical analysis and analytical methods will be developed to isolate climate-vegetation feedbacks and possible nonlinear effects between natural vegetation and land use.

References

Armstrong McKay, D. I., Staal, A., Abrams, J. F., Winkelmann, R., Sakschewski, B., Loriani, S., Fetzer, I., Cornell, S. E., Rockström, J., & Lenton, T. M. (2022). Exceeding 1.5°C global warming could trigger multiple climate tipping points. Science, 377(6611), eabn7950. https://doi.org/10.1126/science.abn7950

Braconnot, P., Viovy, N., & Marti, O. (2025). Dynamic vegetation highlights first-order climate feedbacks and their dependence on the climate mean state. Earth System Dynamics, 16(6), 2113–2136. https://doi.org/10.5194/esd-16-2113-2025