Pollution atmosphérique et climat

National audienceClimate change and air quality are closely related: through the policy measures implemented to mitigate these major environmental threats but also through the geophysical processes that drive them. We designed, developed and implemented a comprehensive regional air quality and climate modelling system to investigate future air quality in Europe taking into account the combined pressure of future climate change and long range transport. Using the prospective scenarios of the last generation of pathways for both climate change (emissions of well mixed greenhouse gases) and air pollutants, we can provide a quantitative view into the possible future air quality in Europe. We find that ozone pollution will decrease substantially under the most stringent scenario but the efforts of the air quality legislation will be adversely compensated by the penalty of global warming and long range transport for the business as usual scenario. For particulate matter, the projected reduction of emissions efficiently reduces exposure levels.Changement climatique et qualité de l'air sont intimement liés : à travers les politiques de gestion mises en oeuvre pour atténuer ces menaces environnementales majeures mais aussi à travers les processus géophysiques qui les gouvernent. Afin de pouvoir étudier l'évolution de la pollution atmosphérique en Europe en prenant en compte l'influence conjointe du changement climatique et du transport à longue distance, nous avons conçu, développé et mis en oeuvre un système complet de modélisation régionale du climat et de la qualité de l'air. En utilisant des scénarios prospectifs de dernière génération relatifs au changement climatique (émissions de gaz à effet de serre) mais aussi pour les polluants à courte durée de vie, nous avons pu proposer une quantification de l'évolution future de la qualité de l'air en Europe. D'après le scénario le plus volontariste, la pollution liée à l'ozone sera réduite de manière substantielle mais les efforts positifs induits par les politiques de gestion de la qualité de l'air seront contrebalancés par le changement climatique et le transport à longue distance pour le scénario statu-quo. En ce qui concerne les particules, les réductions d'émissions futures réduiront de manière efficace les niveaux d'exposition

Geological evidence of extensive N-fixation by volcanic lightning during very large explosive eruptions

La mayor parte del nitrógeno (N) accesible para la vida está atrapado en el dinitrógeno (N 2 ) , la molécula atmosférica más estable. Para ser metabolizado por los organismos vivos, el N 2 debe convertirse en formas biológicamente asimilables, el llamado N fijo. Hoy en día, casi toda la fijación del N se logra mediante procesos biológicos y antropogénicos. Sin embargo, en los primeros ambientes prebióticos de la Tierra, la fijación de N debe haber ocurrido mediante procesos abióticos naturales . Uno de los procesos más invocados son las descargas eléctricas , incluidas las de tormentas eléctricas y relámpagos asociados con erupciones volcánicas. A pesar de la frecuente aparición de relámpagos volcánicos durante las erupciones explosivas y de los convincentes experimentos de laboratorio, no se había encontrado evidencia de una fijación sustancial de N en ningún archivo geológico. Aquí, informamos sobre el descubrimiento de una cantidad significativa de nitrato en depósitos volcánicos de erupciones formadoras de calderas neógenas , que están bien correlacionadas con las concentraciones de especies emitidas directamente por los volcanes (azufre, cloro). La composición multiisotópica (δ18O, Δ17O) de los nitratos revela que se originan a partir de la oxidación atmosférica de los óxidos de nitrógeno formados por rayos volcánicos . Según este primer archivo geológico de nitratos volcánicos, estimamos que, en promedio, se pueden fijar alrededor de 60 Tg de N durante un gran evento explosivo. Nuestros hallazgos sugieren un papel único que potencialmente desempeñan las erupciones explosivas subaéreas en el suministro de elementos esenciales para el surgimiento de la vida en la Tierra

Inter-model comparison of global hydroxyl radical (OH) distributions and their impact on atmospheric methane over the 2000–2016 period

The modeling study presented here aims to estimate how uncertainties in global hydroxyl radical (OH) distributions, variability, and trends may contribute to resolving discrepancies between simulated and observed methane (CH4) changes since 2000. A multi-model ensemble of 14 OH fields was analyzed and aggregated into 64 scenarios to force the offline atmospheric chemistry transport model LMDz (Laboratoire de Meteorologie Dynamique) with a standard CH4 emission scenario over the period 2000–2016. The multi-model simulated global volume-weighted tropospheric mean OH concentration ([OH]) averaged over 2000–2010 ranges between 8:7*10^5 and 12:8*10^5 molec cm-3. The inter-model differences in tropospheric OH burden and vertical distributions are mainly determined by the differences in the nitrogen oxide (NO) distributions, while the spatial discrepancies between OH fields are mostly due to differences in natural emissions and volatile organic compound (VOC) chemistry. From 2000 to 2010, most simulated OH fields show an increase of 0.1–0:3*10^5 molec cm-3 in the tropospheric mean [OH], with year-to-year variations much smaller than during the historical period 1960–2000. Once ingested into the LMDz model, these OH changes translated into a 5 to 15 ppbv reduction in the CH4 mixing ratio in 2010, which represents 7%–20% of the model-simulated CH4 increase due to surface emissions. Between 2010 and 2016, the ensemble of simulations showed that OH changes could lead to a CH4 mixing ratio uncertainty of > 30 ppbv. Over the full 2000–2016 time period, using a common stateof- the-art but nonoptimized emission scenario, the impact of [OH] changes tested here can explain up to 54% of the gap between model simulations and observations. This result emphasizes the importance of better representing OH abundance and variations in CH4 forward simulations and emission optimizations performed by atmospheric inversions

Climate change penalty and benefit on surface ozone: a global perspective based on CMIP6 earth system models

Funder: Hadley CentreFunder: BEISFunder: NERCFunder: Met Office; doi: http://dx.doi.org/10.13039/501100000847Funder: Japan Society for the Promotion of Science; doi: http://dx.doi.org/10.13039/501100001691Funder: Public Investment Program of the Ministry of Development and Investments of GreeceAbstract: This work presents an analysis of the effect of climate change on surface ozone discussing the related penalties and benefits around the globe from the global modelling perspective based on simulations with five CMIP6 (Coupled Model Intercomparison Project Phase 6) Earth System Models. As part of AerChemMIP (Aerosol Chemistry Model Intercomparison Project) all models conducted simulation experiments considering future climate (ssp370SST) and present-day climate (ssp370pdSST) under the same future emissions trajectory (SSP3-7.0). A multi-model global average climate change benefit on surface ozone of −0.96 ± 0.07 ppbv °C−1 is calculated which is mainly linked to the dominating role of enhanced ozone destruction with higher water vapour abundances under a warmer climate. Over regions remote from pollution sources, there is a robust decline in mean surface ozone concentration on an annual basis as well as for boreal winter and summer varying spatially from −0.2 to −2 ppbv °C−1, with strongest decline over tropical oceanic regions. The implication is that over regions remote from pollution sources (except over the Arctic) there is a consistent climate change benefit for baseline ozone due to global warming. However, ozone increases over regions close to anthropogenic pollution sources or close to enhanced natural biogenic volatile organic compounds emission sources with a rate ranging regionally from 0.2 to 2 ppbv C−1, implying a regional surface ozone penalty due to global warming. Overall, the future climate change enhances the efficiency of precursor emissions to generate surface ozone in polluted regions and thus the magnitude of this effect depends on the regional emission changes considered in this study within the SSP3_7.0 scenario. The comparison of the climate change impact effect on surface ozone versus the combined effect of climate and emission changes indicates the dominant role of precursor emission changes in projecting surface ozone concentrations under future climate change scenarios

Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence

Intergovernmental Panel on Climate Change (IPCC) assessments are the trusted source of scientific evidence for climate negotiations taking place under the United Nations Framework Convention on Climate Change (UNFCCC). Evidence-based decision-making needs to be informed by up-to-date and timely information on key indicators of the state of the climate system and of the human influence on the global climate system. However, successive IPCC reports are published at intervals of 5–10 years, creating potential for an information gap between report cycles. We follow methods as close as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One (WGI) report. We compile monitoring datasets to produce estimates for key climate indicators related to forcing of the climate system: emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. The purpose of this effort, grounded in an open-data, open-science approach, is to make annually updated reliable global climate indicators available in the public domain (https://doi.org/10.5281/zenodo.11388387, Smith et al., 2024a). As they are traceable to IPCC report methods, they can be trusted by all parties involved in UNFCCC negotiations and help convey wider understanding of the latest knowledge of the climate system and its direction of travel. The indicators show that, for the 2014–2023 decade average, observed warming was 1.19 [1.06 to 1.30] °C, of which 1.19 [1.0 to 1.4] °C was human-induced. For the single-year average, human-induced warming reached 1.31 [1.1 to 1.7] °C in 2023 relative to 1850–1900. The best estimate is below the 2023-observed warming record of 1.43 [1.32 to 1.53] °C, indicating a substantial contribution of internal variability in the 2023 record. Human-induced warming has been increasing at a rate that is unprecedented in the instrumental record, reaching 0.26 [0.2–0.4] °C per decade over 2014–2023. This high rate of warming is caused by a combination of net greenhouse gas emissions being at a persistent high of 53±5.4 Gt CO2e yr−1 over the last decade, as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that the rate of increase in CO2 emissions over the last decade has slowed compared to the 2000s, and depending on societal choices, a continued series of these annual updates over the critical 2020s decade could track a change of direction for some of the indicators presented here.HORIZON EUROPE Framework ProgrammeH2020 European Research CouncilResearch Councils UKEngineering and Physical Sciences Research CouncilPeer Reviewe

IPCC, 2023: Climate Change 2023: Synthesis Report, Summary for Policymakers. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland.

This Synthesis Report (SYR) of the IPCC Sixth Assessment Report (AR6) summarises the state of knowledge of climate change, its widespread impacts and risks, and climate change mitigation and adaptation. It integrates the main findings of the Sixth Assessment Report (AR6) based on contributions from the three Working Groups1 , and the three Special Reports. The summary for Policymakers (SPM) is structured in three parts: SPM.A Current Status and Trends, SPM.B Future Climate Change, Risks, and Long-Term Responses, and SPM.C Responses in the Near Term.This report recognizes the interdependence of climate, ecosystems and biodiversity, and human societies; the value of diverse forms of knowledge; and the close linkages between climate change adaptation, mitigation, ecosystem health, human well-being and sustainable development, and reflects the increasing diversity of actors involved in climate action. Based on scientific understanding, key findings can be formulated as statements of fact or associated with an assessed level of confidence using the IPCC calibrated language

Dilemmes de la géo-ingénierie climatique

International audienceA mesure que les effets du changement climatique se font de plus en plus dramatiques et que la fenêtre d'opportunité d'un développement soutenable et résilient du point de vue climatique est en train de se refermer, les recherches sur la géoingénieurie sont de plus en plus discutées. La géoingénieurie climatique vise à "corriger" le climat à grande échelle pour pallier l'effet des activités humaines. Sur la base de la sixième évaluation du GIEC, achevée mi-2023, et du rapport intermédiaire de la commission mondiale d'éthique des sciences et technologies de l'UNESCO, nous expliquons ici les motivations qui sous-tendent ces projets, les nouveaux risques qu'ils font courir aux personnes et écosystèmes et la difficulté de positionnement des chercheurs

Dilemmes de la géo-ingénierie climatique

A mesure que les effets du changement climatique se font de plus en plus dramatiques et que la fenêtre d'opportunité d'un développement soutenable et résilient du point de vue climatique est en train de se refermer, les recherches sur la géoingénieurie sont de plus en plus discutées. La géoingénieurie climatique vise à "corriger" le climat à grande échelle pour pallier l'effet des activités humaines. Sur la base de la sixième évaluation du GIEC, achevée mi-2023, et du rapport intermédiaire de la commission mondiale d'éthique des sciences et technologies de l'UNESCO, nous expliquons ici les motivations qui sous-tendent ces projets, les nouveaux risques qu'ils font courir aux personnes et écosystèmes et la difficulté de positionnement des chercheurs

Dilemmes de la géo-ingénierie climatique

International audienceA mesure que les effets du changement climatique se font de plus en plus dramatiques et que la fenêtre d'opportunité d'un développement soutenable et résilient du point de vue climatique est en train de se refermer, les recherches sur la géoingénieurie sont de plus en plus discutées. La géoingénieurie climatique vise à "corriger" le climat à grande échelle pour pallier l'effet des activités humaines. Sur la base de la sixième évaluation du GIEC, achevée mi-2023, et du rapport intermédiaire de la commission mondiale d'éthique des sciences et technologies de l'UNESCO, nous expliquons ici les motivations qui sous-tendent ces projets, les nouveaux risques qu'ils font courir aux personnes et écosystèmes et la difficulté de positionnement des chercheurs