Laboratoire des Sciences du Climat et de l'Environnement

Lithospheric delamination involves short-lived crustal and surface responses, alkaline magmatism, high heat flow and extension. In the Western Mediterranean, delamination is hypothesized to have triggered uplift at the origin of the Messinian Salinity Crisis (MSC). But delamination as the primary cause of uplift is questioned due to the insufficient temporal resolution. We report new U-Pb ages and clumped isotope analyses from calcite veins formed in an eastern Betic intramontane basin. They reveal a brief fluid event from 8.5 to 5 Ma linked to extension and retreating delamination. After extension, shortening and uplift began at 4.5–3 Ma across the boundary between the Cabo de Gata arc basement and the Iberia margin. We show that the MSC occurred before shortening and during delamination. Slab detachment caused the demise of the MSC, the formation of a new plate boundary fault and tectonic escape between Africa and Iberia around 5 Ma.

Methane is an important greenhouse gas¹ and its atmospheric concentration has almost tripled since pre-industrial times2, 3–4. Atmospheric methane mixing ratios vary seasonally, with the seasonal cycle amplitude (SCA) having decreased in northern high latitudes and increased in the subtropics and tropics since the 1980s5,6. These opposing SCA trends can help understanding of long-term changes in the global methane budget, as methane emissions and sinks have opposing effects on the SCA⁵. However, trends in the methane SCA have not yet been explored in detail5,6. Here we use a suite of atmospheric transport model simulations and attribute the observed trends in the seasonal amplitude of methane to changes in emissions and the atmospheric sink from reaction with the hydroxyl radical (OH). We find that the decreasing amplitude in the northern high latitudes is mainly caused by an increase in natural emissions (such as wetlands) owing to a warmer climate, adding evidence to previous studies suggesting a positive climate feedback7, 8–9. In contrast, the enhanced methane amplitude in the subtropics and tropics is mainly attributed to strengthened OH oxidation. Our results provide independent evidence for an increase in tropospheric OH concentration10,11 of 10 ± 1% since 1984, which together with an increasing atmospheric methane concentration suggests a 21 ± 1% increase in the atmospheric methane sink.

Natural dust storms are associated with changes to atmospheric photochemical processes, including changes in surface ozone, a critical global air pollutant. Here, we quantified the change in surface ozone during dust storms for regions in China by using a synthesis of measurements and modeling approaches. Our results showed that notable reductions of the average ozone concentration (2.0 to 12.2 parts per billion by volume) were observed during the 12 dust storm events from 2016 to 2023, relative to predust storm levels. The chemical interactions of dust particles with ozone production processes played crucial roles in explaining approximately 13 to 35% of the observed ozone reduction, alongside the impact of intense meteorological disturbances on transport and formation of ozone. Among these interactions, the uptake of ozone, reactive nitrogen, and hydroperoxyl radical by dust particles could substantially contribute to the ozone suppression. This study highlighted the importance of interactions between severe dust pollution and atmospheric photochemistry.

Water scarcity is a global challenge in many emerging economies, including China. China is one of the most extensive freshwater users and has set water efficiency improvement goals for 2030 at the prefecture level. However, no systematic water use and savings comparison exists across prefectures and sectors. Here, we used datasets of water withdrawal for 10,608 industrial and 1715 agricultural sub-sectors for 343 prefectures, and explored the opportunities to reduce water use. Results show that 10% of the least water-efficient industrial sub-sectors represent a disproportionate 46% water use. 18.9 km³ (±3.2%) water saving in industry and 50.3 km³ (±2.3%) in agriculture could be achieved, equivalent to Russia’s annual demand. A minority of sectors, including cloth(ing)- and chemical-manufacturing, rice-, vegetable- and fruit-cultivation, could contribute the most to water savings. Our study is essential for identifying water use and efficiency information for individual prefectures and sectors.

Optimal preservation of tissues from the field to long‐term cryo‐storage is paramount to securing genetic resources for research needs. DNA preservation techniques vary, with flash freezing currently considered the gold standard in tissue preservation. However, flash freezing tissue samples in the field presents challenges, necessitating a more comprehensive understanding of the quantity and quality of preserved DNA from different techniques in archival collections. We compared metrics from DNA extractions from field‐collected amphibian, squamate and bird tissues from archival collections that were flash‐frozen in liquid nitrogen or fixed in either ethanol or tissue lysis buffer prior to archival cryopreservation. We also included DNA extracted from tissues of known liquid nitrogen tank failures to provide a baseline of DNA degradation under the very worst‐case scenario. Flash‐frozen tissues often preserved higher yields of DNA, but peak fragment size, the percentage of fragments larger than 10 kb and DNA integrity numbers were all significantly reduced compared to tissues first preserved in fixative buffers. This pattern was observed across independent samples and between flash‐frozen and buffer‐preserved pair replicates. Degradation seen in flash‐frozen tissues was also distinct to tissues from known tank failures. We suggest that degradation in flash‐frozen tissues occurred during shipping, sample sorting/accession or during subsequent subsampling when tissues may partially or fully thaw, exposing DNA to damaging freeze–thaw processes. By contrast, tissues in fixative buffers were likely protected from freeze–thaw damage. This study highlights that using multiple field preservation methods and minimising freeze–thaw cycles for flash‐frozen tissues may provide the most robust protection against the DNA degradation sources encountered by field collections.

The North Atlantic Deep Water (NADW) is a key component of modern climate systems, redistributing heat from equatorial to polar regions and contributing to the Atlantic Meridional Overturning Circulation. However, the timing of its emergence and the mechanisms driving its formation remain uncertain. This study explores ocean circulation patterns during the middle Eocene (48–38 Ma) and early Miocene (23–16 Ma) using simulations with the IPSL‐CM5A2 climate model. In the middle Eocene simulations, reduced surface salinity in the North Atlantic prevents NADW formation, regardless of atmospheric CO2 $C{O}_{2}$ levels or the presence of an Antarctic ice sheet. Conversely, early Miocene simulations suggest that paleogeographic shifts promote higher Atlantic salinity, enabling NADW formation. Specifically, the closure of the Polish Strait and the narrowing of the Central American Seaway enhance salt retention in the Atlantic and increase salt transport from subtropical to subpolar regions. Additionally, changes in African monsoonal precipitation—characterized by a reduction and eastward shift across Central Africa—reduce freshwater influx into the Atlantic between the middle Eocene and early Miocene. These combined factors weaken North Atlantic stratification, facilitating NADW development during the early Miocene. This research provides a timeline for NADW initiation and insights into the processes driving its formation.

Accurate mapping of vegetation canopy height and biomass distribution is essential for effective forest monitoring, climate change mitigation, and sustainable forestry. Here we present high-resolution remote sensing-based canopy height (10 m resolution) and above ground biomass (AGB, 50 m resolution) maps for the forests of the Iberian Peninsula from 2017 to 2021, using a deep learning framework that integrates Sentinel-1, Sentinel-2, and LiDAR data. Two UNET models were developed: one trained on Airborne Laser Scanning (ALS) data (MAE: 1.22 m), while another using Global Ecosystem Dynamics Investigation (GEDI) footprints (MAE: 3.24 m). External validation with 6,308 Spanish National Forest Inventory (NFI) plots (2017–2019) confirmed canopy height reliability, showing MAEs of 2–3 m in tree-covered areas. AGB estimates were obtained through Random Forest models that linked UNET derived height predictions to NFI AGB data, achieves an MAE of ~29 Mg/ha. The creation of high-resolution maps of canopy height and biomass across various forest landscapes in the Iberian Peninsula provides a valuable new tool for environmental researchers, policy makers, and forest management professionals, offering detailed insights that can inform conservation strategies, carbon sequestration efforts, and sustainable forest management practices.

Because of human population growth and changes in diet, global livestock and associated ammonia , emissions are projected to increase through the end of the century, with possible impacts on atmospheric chemistry and climate. In this study, we propose a methodology to project global gridded livestock densities and emissions from agriculture until 2100. Based on a downscaling method, future livestock distribution has been estimated until 2100 for three Shared Socio‐economic Pathways (SSP2‐4.5, SSP4‐3.4, and SSP5‐8.5) and used in a global process‐based model (Calculation of AMmonia Emissions in ORCHIDEE, CAMEO) to estimate agricultural ammonia emissions during the 21st century. Emissions under SSP4‐3.4 and SSP5‐8.5 calculated by CAMEO compare well with the range estimated by the Integrated Assessment Models (IAM; 50 to 66 ) in the framework of the Phase 6 of the Coupled Model Intercomparison Project (CMIP6). Some opposite trends arise under SSP2.4‐5 where CAMEO emissions increase consistently in response to the increasing trends in synthetic fertilizer use under this scenario. Africa is identified as the most emitting region worldwide, with emissions ranging from 10 to 16 in 2100. Through a set of simulations, we estimated climate change as responsible for 20 % of future increase in emissions. The produced data sets of future emissions is an alternative option to IAM‐based emissions for studies aiming at projecting the evolution of atmospheric chemistry and its impact on climate. Further model developments involving the bi‐directional property of and refinement in the future changes of agricultural practices constitute interesting perspectives.

Since spring 2023, global mean temperatures have surged, repeatedly surpassing historical monthly records. Although various causes have been proposed, their relative contributions remain unclear. Here we show that, using a novel attribution framework that combined a reduced complexity model with an observationally constrained statistical model, we recreated the annual global temperature for 1855-2024 with strong agreement with observations (r = 0.99). This approach captures key previous climate variations, including mid-20th century cooling, the 1998-2012 warming slowdown, and the recent temperature spike. We found that the 2022-2024 warming relative to the 2010-2021 level was caused mainly by an increase in atmospheric carbon dioxide (41%, 95% confidence interval: 35-50%) and a surge in the Atlantic Multidecadal Oscillation (39%, 23-50%), followed by the ascending solar cycle (9%, 1-19%). Our results suggest that the ongoing rise in carbon dioxide concentration has intensified recent warming. These coincidental peaks and troughs in anthropogenic and natural drivers may increase the likelihood of extreme temperature events.

The neodymium isotope signatures (εNd) of the authigenic fraction have been extensively used to reconstruct past seawater εNd and hydrological circulation. Among the various methods, sequential extraction of hydrogenic ferromanganese oxyhydroxides from bulk sediments represents a rapid and straightforward approach that may potentially induce artifacts due to the potential release of non‐seawater‐derived Nd during the extraction procedure. Here we investigated different methods for extracting past seawater Nd isotope compositions from a core collected in the Adriatic Sea whose tephra layers have been previously well documented. We analyzed εNd in planktonic foraminifera samples and in non‐decarbonated sediment leachates obtained with three solutions commonly used in the context of the Mediterranean Sea: (a) 0.02 M hydroxylamine hydrochloride (HH) solution, (b) 1N HCl, and (b) a 25% (v/v) acetic acid (AA). Our results show that (a) the foraminiferal εNd remains unaffected by the diagenesis of tephra content; (b) all three methods indicate significantly more radiogenic εNd values in tephra levels (up to 1.5 εNd unit), which is attributed to tephra dissolution accounting for 2.7% of extracted Nd; (c) of the three leaching methods applied to samples with low tephra content, hydroxylamine hydrochloride (HH) yields εNd values that are more consistent with those obtained on planktonic foraminifera; (d) the εNd values of planktonic foraminifera in core MD90‐917 remained constant indicating that the Adriatic deep water primarily reflects the local Nd isotope composition over the last 20 kyr.

While past major climate transitions can be unequivocally identified, understanding of underlying mechanisms and timescales remains limited. We employ a dimensional analysis of benthic stable isotope records across different timescales to uncover how Cenozoic climatic fluctuations are associated with changes in the number of feedbacks and mechanisms involved. Our analysis indicates that warmer and colder climates respond substantially differently to orbital forcing. Notably, large numbers of feedbacks dominated during the Icehouse (3.3 Ma to present) state at obliquity and eccentricity timescales, and during the Warmhouse (66–56 Ma and 47–34 Ma) and Hothouse (56–47 Ma) states at precession timescales. During the Coolhouse (34–3.3 Ma) state the number of active feedbacks was low and had no dominant timescale. Coupling between climate signals that affect oxygen and carbon isotope records appears high only in the Icehouse state, and low to absent in all other states. We also find that anomalously high active feedback numbers and very high coupling occurred across all timescales during the Paleocene-Eocene Thermal Maximum (PETM, 56 Ma), which suggests a complete system perturbation. In conclusion, our findings challenge the notion of a simple and unique conceptual model of interconnected feedbacks in reproducing Cenozoic paleoclimate variability, given that different numbers of active feedbacks with different levels of coupling governed different timescales between climate states, which then affected the inherent (in-)stability of each climate state.

As part of the REgional Carbon Cycle Assessment and Processes‐2 (RECCAP‐2) project of the Global Carbon Project, here we estimate the GHG budgets (anthropogenic and natural sources and sinks) for the South Asia (SA) region as a whole and each country (Afghanistan, Bangladesh, Bhutan, India, Nepal, Pakistan, and Sri Lanka) for the decade of 2010–2019 (2010s). Countries in the region are experiencing a rapid rise in fossil fuel consumption and demand for agricultural land, leading to increased deforestation and higher greenhouse gas emissions. This study synthesizes top‐down (TD) and bottom‐up (BU) dynamic global vegetation model results, BU GHG inventories, ground‐based observation upscaling, and direct emissions for major GHGs. The fluxes for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) analyzed include fossil fuel emissions, net biome productivity, land use change, inland waters, wetlands, and upland and submerged soils. Our analysis shows that the overall total GHG emissions contributed to a net increase of 34%–43% during the 2010s compared to the 2000s, primarily driven by industrial activities. However, terrestrial ecosystems acted as a notable exception by serving as a CO2 sink in the 2010s, effectively sequestering atmospheric carbon. The sink was significantly smaller than overall carbon emissions. Overall, the 2010s GHG emissions based on BU and TD were 4,517 ± 639.8 and 4,532 ± 807.5 Tg CO2 eq, with CO2, CH4, and N2O emissions of 2165.2 ± 297.1, 1,404 ± 95.9, and 712 ± 466 Tg CO2 eq based on BU models 2,125 ± 515.1, 1,531 ± 205.2, and 876 ± 446.0 Tg CO2 eq based on TD models. Total emissions from SA in the 2010s accounted for approximately 8% of the global share. The terrestrial CO2 sinks estimated by the BU and TD models were 462.9 ± 195.5 and 210.0 ± 630.4 Tg CO2, respectively. Among the SA countries, India was the largest emitter contributing to 80% of the region's total GHG emissions, followed by Pakistan (10%) and Bangladesh (7%).

The age of the Senèze mammalian fauna has been discussed since it was first reported in 1892. 40Ar/39Ar ages reported by Nomade et al. (2014) and recalculated here to agree with current standards placed the deposits between 2.20 and 2.07 Ma. Paleomagnetic data collected in 2001 and 2004 help to narrow the age range, especially of the levels yielding fossils in 2001–2006. In the western sector, fossils can be securely dated between 2.10 and 2.08 Ma, while in the southeastern sector, they are slightly older, between 2.20 and 2.18 Ma. Senèze is one of the few later Cenozoic European sites dated by both argon geochronometry and paleomagnetism, which makes these ages so precise. Experiments with ESR/U-series dating on teeth proved unsuccessful as a result of the early U-uptake and high natural dose rate in the sediments of Senèze.

The new fieldwork at Senèze ran from 2000 to 2006, with the goals of clarifying the age, stratigraphy and taphonomy of Senèze, as well as finding additional remains, especially of the less well-known taxa. Here we summarize the findings of each chapter and discuss their broader implications. Four geological chapters consider field methods, stratigraphy, volcanology and tephra mineralogy and dating. Following a chapter on palynology, two chapters discuss non-mammalian paleontology: ichthyology and ornithology. Eight chapters cover work on the fossil mammals. The chapter on biochronology places Senèze among other sites at the start of MNQ 18. Based on that work and the mammal chapters, it is possible to review the relative frequency of mammalian families in the total Senèze assemblage. Of some 2200 specimens, over half are cervids, with bovids, rhinocerotids and equids far behind. According to data from palynology and the habitat preferences of the more common mammals, the paleoenvironment around the Senèze maar would have included forest, woodland and grassland, perhaps in a warmer and moister climate than today. Taphonomic studies revealed that bones often rested a long time under water, lacked any indication of carnivore attack and often displayed pathologies in their joints. Combining these results and those from stratigraphy, it is proposed that most associated skeletons were preserved after large mammals fell into the lake and drowned without being disturbed.

Afforestation and reforestation, both of which refer to forestation strategies, are widely promoted as key tools to mitigate anthropogenic warming. However, the carbon sequestration potential of these efforts remains uncertain in satellite-based assessments, particularly when accounting for dynamic climate conditions, vegetation-climate feedback, fire-dominated disturbance, and the trade-offs associated with surface albedo changes. Leveraging a coupled Earth system model, we estimated that global forestation mitigates 31.3 to 69.2 Pg C eq (carbon equivalent) during 2021–2100 under a sustainable shared socioeconomic pathway. Regionally, the highest carbon mitigation potential of forestation concentrates in tropical areas, while mid-high-latitude regions demonstrate higher heterogeneity, highlighting the need for region-specific strategies and further refinement of nature-based mitigation plans. Our findings underscore the importance of considering disturbances and minimizing adverse albedo changes when estimating the carbon mitigation potential of forestation initiatives. We also advocate for the development of consistent, high-resolution maps of suitable areas for targeted forestation, avoiding environmentally sensitive lands and potential conflicts with other human activities.

Targeting urban air quality improvements in India, the National Clean Air Program (NCAP) was launched in 2019 to reduce PM2.5 concentrations by 20%–30% in 122 initial cities over a 7 year period (2017–2024). However, considering the regional nature of air pollution nationwide and the significant emission load from rural areas, a potentially large fraction of urban PM2.5 might originate from emissions outside of a city’s boundary, i.e. transboundary emissions. Here, we couple top-down (STILT-PM2.5) and bottom-up (WRF-Chem) modeling approaches with a new, nationwide, monthly-resolved, and fine-scale (5 km × 5 km) anthropogenic emission inventory to assess the impact of transboundary emissions to urban PM2.5 concentrations across 143 cities (122 NCAP and 67 million plus -cities with population >1 million, among which 46 cities are also NCAP cities). We find that, on average, ∼85% (STILT-PM2.5: 82% [95% CI: 80–85%; IQR: 77%–94%] & WRF-Chem: 89% [95% CI: 87%–91%; IQR: 88%–96%]) of urban PM2.5 across the 143 cities originates from transboundary emissions, with domestic biomass burning (32%), energy generation (16%) and industry (15%) being the leading average emission sources to the transboundary contribution. In addition, 107 of the 122 NCAP cities from both modeling approaches have annual transboundary PM2.5 contributions exceeding 80%, indicating that an entire mitigation of within-boundary emissions alone in these cities will not achieve the most conservative targets outlined as part of NCAP. Our findings underscore the need for multi-scale, regional action planning and implementation to achieve PM2.5-air quality targets throughout India.

The Net Ecosystem Carbon Balance (NECB) is a crucial metric for understanding integrated carbon dynamics in Arctic and boreal regions, which are vital to the global carbon cycle. These areas are associated with significant uncertainties and rapid climate change, potentially leading to unpredictable alterations in carbon dynamics. This mini-review examines key components of NECB, including carbon sequestration, methane emissions, lateral carbon transport, herbivore interactions, and disturbances, while integrating insights from recent permafrost region greenhouse gas budget syntheses. We emphasize the need for a holistic approach to quantify the NECB, incorporating all components and their uncertainties. The review highlights recent methodological advances in flux measurements, including improvements in eddy covariance and automatic chamber techniques, as well as progress in modeling approaches and data assimilation. Key research priorities are identified, such as improving the representation of inland waters in process-based models, expanding monitoring networks, and enhancing integration of long-term field observations with modeling approaches. These efforts are essential for accurately quantifying current and future greenhouse gas budgets in rapidly changing northern landscapes, ultimately informing more effective climate change mitigation strategies and ecosystem management practices. The review aligns with the goals of the Arctic Monitoring and Assessment Program (AMAP) and Conservation of Arctic Flora and Fauna (CAFF), providing important insights for policymakers, researchers, and stakeholders working to understand and protect these sensitive ecosystems.

Accurate accounting of greenhouse‐gas (GHG) emissions and removals is central to tracking progress toward climate mitigation and for monitoring potential climate‐change feedbacks. GHG budgeting and reporting can follow either the Intergovernmental Panel on Climate Change methodologies for National Greenhouse Gas Inventory (NGHGI) reporting or use atmospheric‐based “top‐down” (TD) inversions or process‐based “bottom‐up” (BU) approaches. To help understand and reconcile these approaches, the Second REgional Carbon Cycle Assessment and Processes study (RECCAP2) was established to quantify GHG emissions and removals for carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), for ten‐land and five‐ocean regions for 2010–2019. Here, we present the results for the North American land region (Canada, the United States, Mexico, Central America and the Caribbean). For 2010–2019, the NGHGI reported total net‐GHG emissions of 7,270 TgCO2‐eq yr⁻¹ compared to TD estimates of 6,132 ± 1,846 TgCO2‐eq yr⁻¹ and BU estimates of 9,060 ± 898 TgCO2‐eq yr⁻¹. Reconciling differences between the NGHGI, TD and BU approaches depended on (a) accounting for lateral fluxes of CO2 along the land‐ocean‐aquatic continuum (LOAC) and trade, (b) correcting land‐use CO2 emissions for the loss‐of‐additional‐sink capacity (LASC), (c) avoiding double counting of inland water CH4 emissions, and (d) adjusting area estimates to match the NGHGI definition of the managed‐land proxy. Uncertainties remain from inland‐water CO2 evasion, the conversion of nitrogen fertilizers to N2O, and from less‐frequent NGHGI reporting from non‐Annex‐1 countries. The RECCAP2 framework plays a key role in reconciling independent GHG‐reporting methodologies to support policy commitments while providing insights into biogeochemical processes and responses to climate change.

Aim Testing the impact of climate on diversification is a major goal of evolutionary biology. Birth‐death models like palaeoenvironment‐dependent diversification (PDD) models, for example, allow exploring the potential correlations between diversification dynamics and past environmental changes, such as temperature, among other abiotic variables. So far, such studies have been limited to proxy‐derived global temperature trends, because these are the only temperature records that are easily accessible and almost continuous over multimillion‐year periods. Innovation In this study, we propose a methodology to generate spatialised and/or seasonal palaeotemperature time series. To do so, we take advantage of temperature variables simulated by climate models for several ‘snapshots’ of the last 100 million years. Based on the hypothesis that a long‐term global temperature drift is imprinted, to some degree, on all regional and seasonal temperature records, we use the global proxy‐derived temperature record as the mean of interpolation between discrete climate simulations. We then evaluate the possibility of constraining the PDD models, as implemented in RPANDA, with these hybrid temperature time series. We assess if these regional and seasonal temperature trends may be more relevant to the evolutionary history of a given clade than the global temperature record used so far. Main Conclusions Our results show that PDD models using seasonal and/or regional hybrid temperature time series tend to receive high statistical support. This offers promising perspectives for refining our understanding of the impact of regional and seasonal temperature evolution on diversification dynamics, and calls for continuing development of deep‐time palaeoclimate modelling and interdisciplinary studies.