Socio-economic scenarios and resulting global warming levels structure the understanding of causal chains of greenhouse gas emissions, air pollution control, land-use changes, the response of the Earth system, climatic impact-drivers, exposure, vulnerability, adaptation responses, and climate-related risks. Following the French Academy of Sciences workshop on “The climate emergency, a turning point” (2024), this manuscript provides an overview of the concepts and methodologies underpinning the Sixth Assessment Report of the Intergovernmental panel on Climate Change (IPCC) regarding the development of scenarios and the assessment of risks from the perspective of the physical science basis of climate change, and selected recent updates and advances. It includes (i) a brief overview of the current state of the global and regional climate and impacts in France, (ii) an overview of future warming scenarios spanning socio-economic scenarios, (iii) constrained climate projections for global warming, and (iv) low-likelihood, high-impact outcomes which are relevant to inform robust decision-making and risk management.
Over the past thirty years, the silicon cycle at the scale of continental ecosystems has become an important topic within the scientific community. Since the 1990s, this research has been driven primarily by growing awareness of the need to quantify the impact of anthropogenic activities on the environment, as well as by advances in understanding the beneficial role of silicon in cultivated plants and its application in agricultural practices. This review highlights the major developments in the study of the silicon cycle at the soil-plant scale since the pioneering work of Bartoli, particularly his cycle model (Bartoli, F. Environ. Biogeochem. Ecol. Bull. 35 (1983), pp. 469–476). Phytoliths are now recognized as key players in the silicon cycle at both local and global scales. They represent a significant source of dissolved silicon (DSi), especially in highly weathered soils. Human activities such as deforestation, grazing, agriculture, and urban land use have been shown to disrupt the Si cycle. The concept of plant-available silicon indicator (PAS) has been developed and is now used alongside other routine soil parameters (e.g., pH and grain size) to identify the drivers of DSi. In the future, greater attention should be given to the determination and the dynamics of the available Si pools in plants, the quantification of the effects of biological factors other than plants, and the impact of atmospheric silicon inputs. The main factors influencing the terrestrial biogeochemical cycle of silicon should be integrated into models to predict the evolution of silicon in soils.
We examine the accumulation and provenance of non-ferrous metals in a shallow peat sequence (60 cm) collected in the Valley of Chassezac (Narcettes, Cevennes) in the French Massif Central (FMC), one of the oldest mining districts in Europe. The core is dated between the Modern period (<250 years old) and the 5th millennium BCE ( 14 C and pollens). Trace metal (Pb, As, Sb, Cu, Ni, Zn) enrichments generally increase from mid-core at 31 cm [70 CE–180 BCE] to the top, with maxima during the Modern period (0–18 cm, <250 yr). Statistical analyses (Principal Component Analysis and a source apportionment MixSIAR Bayesian model) applied to trace metals and stable Pb isotopes enable to discriminate the excess Pb imprint and its geographic provenance from Pb–Ag mining in France and surrounding countries within the first 31 cm. The most striking findings are the almost non-existent imprint from the numerous Spanish mines and the overwhelming French and Italian source imprints. Few Greek mines also contribute Pb enrichment, most particularly at depth, during the Roman period and late Iron Age. As expected from its proximity to the Narcettes core, the FMC (northern area and the mont Lozère) and mines from the Alps dominate the French contribution. The significant input from the mont Lozère extends its well-known medieval Ag–Pb exploitation into the Roman, and possibly, Gallic periods. Finally, a specific enrichment centered at 47–51 cm [3.2–4.1 ky BCE] is clearly discerned for Zn, Cu and Ni that may be associated with indigenous Cu smelting from nearby Cu mining districts in the Languedoc region (Cabrières and Roquemengarde). This finding would signify one of the oldest atmospheric metal contamination at a remote French site.
This paper synthesizes recent research conducted within the framework of the Human–Environment Observatory (OHM) Pyrenees Haut-Vicdessos, focusing on long-term environmental contamination in this Pyrenean mountain territory. Drawing on studies in biogeochemistry, paleoecology, and atmospheric sciences, it contrasts two persistent pollutants with distinct temporal trajectories: lead and atmospheric microplastics. Lead represents a legacy contaminant linked to centuries of mining and industrial activity, whereas microplastics, whose accumulation has sharply increased since the 1950s, exemplify an emerging and globally distributed form of pollution reaching even remote mountain environments. Together, these investigations illustrate how past and present human activities leave lasting chemical imprints in high-altitude ecosystems. They also open new questions about the persistence, mobility, and ecological consequences of emerging pollutants, underscoring the need for integrated monitoring and risk-assessment strategies in mountain environments.
Groundwater systems are components of the Critical Zone, in dynamic balance with the climate and human pressure. Water and heat fluxes control biogeochemical processes and regulate both resource potential and system vulnerability. Evaluating system responses to climate and land use changes requires an estimation of subsurface structure, flow dynamics, and the spatial distribution of recharge and discharge zones. Classical hydrological data, such as water levels and river discharge, are commonly coupled with unconventional methodologies, including heat tracing, electrical resistivity tomography, and surface wave analysis. Their coupling via time-lapse monitoring and inversion frameworks enables the characterization of thermal, electrical, and mechanical interactions, thus encouraging a transition from static structure description to transient representations of groundwater. We identify key challenges, including data limitations, model uncertainty propagation, and the integration of transient variables and parameters into inversion workflows. Petrophysical and geostatistical approaches help overcome these issues by coupling geophysical and groundwater models, quantifying spatio-temporal uncertainties, and addressing scale change. Finally, choices regarding experimental design, parameter reduction, dimensionality, model hypotheses, and inversion scale must be assessed to balance parsimony with model accuracy. These developments underscore the central role of hydrogeophysics in advancing Critical Zone science and sustainable groundwater management. Emphasizing transient processes is essential for capturing how subsurface systems evolve over time in response to environmental changes.
