The level of oxygen in the Earth’s atmosphere is unique in our solar system and reflects the long history of life on Earth. It also leads to a singular oxidizing chemistry that regulates the levels of atmospheric reactive trace gases. This is of importance since some of these reactive gases, even if in trace amount, can strongly interact with life and climate. Indeed, reactive trace gases might have been key factors in massive life extinctions in the deep past via abrupt climate warming, the collapse of the stratospheric protective ozone layer, or intense acid rains. During the Cenozoic era (the last 66 Ma), environmental conditions have vastly varied but these changes, less abrupt or more localized than previously in the Earth history, have allowed life to diversify continuously and allowed in particular the mammalian evolution. If there were changes in the atmospheric composition, notably oxidizing capacity, during this period, those changes should therefore have been spatially limited or of moderate amplitude. Yet the Cenozoic era covers a wide variety of environmental conditions related to a gradual cooling of the climate of great amplitude (> 20 ° C) from a hot world, with a very strong greenhouse effect allowing tropical vegetation at high latitudes and very active carbon and nitrogen biogeochemical cycles, to the current glacial climate. In such varied climate and environments, one can expect modifications in the regulation of reactive compounds by atmospheric chemistry. Over the last decade, field observations and then laboratory and theoretical works have revealed chemical mechanisms involved in the pristine atmospheres, such as the recycling of radicals over forests or a new halogenated chemistry over the oceans. This has definitely changed our vision of the oxidising capacity of the atmosphere in untouched areas. In PaleOX, we aim to explore how the oxidizing capacity of the atmosphere has evolved throughout the Cenozoic era and how this has affected the lifetime of reactive short-lived climate forcers such as ozone or methane. To this end, PaleOX aims to study the atmospheric reactivity for five key periods of the Cenozoic by bridging the gap between the cutting-edge past climate modelling methodologies and the state of the art in atmospheric chemistry. A new Earth system model with up-to-dated representations of pristine atmospheric chemistry at its heart will be assembled to simulate consistently atmospheric chemical composition and climate at different stages of the Cenozoic. In parallel, unreleased samples of volcanic sulfate deposits coupled with advanced analysis of their isotopic composition will bring new information on the importance of past atmospheric oxidation pathways, bringing valuable constrains to the numerical analyses. The ultimate goal of this project is to determine how the self-cleaning capacity of the atmosphere changed during the Cenozoic era taking into account information and assumptions about the evolution of vegetation, fires and climatic constraints based on various proxies available in the literature. The fact that modelling methodologies currently used to study deep time climates tend to neglect interactions between chemical cycles of short lived climate forcers and climate will be examined. The possible role of these chemistry-climate links in modulating climate change and gradients will be explored and conditions of surfaces (e.g. UV levels, concentrations of compounds that can alter the functioning of ecosystems, acid deposition) will be characterized. The feedback loops induced by changes in chemical composition of the atmosphere will be assessed in various contexts.

Laser absorption techniques are increasingly used for isotope ratio measurements. These methods offer specific advantages such as the ability to discriminate between isobaric isotopologues (e.g., 16O-13C-16O vs 16O-12C-17O). Their precision, however, still lags behind that of modern mass spectrometers. This project aims to develop an integrated dual-inlet laser spectrometer capable of measuring isotopologue ratios in CO2 with an internal precision on the order of 0.01 permil, allowing measurements of subtle but significant isotopic anomalies in the oxygen isotope ratios (18O/16O and 17O/16O) of atmospheric CO2 and/or carbonate minerals. The corresponding “O-17 excess” (Delta-17O) is an important tracer of atmospheric chemistry and paleo-hydrology, but its measurement in CO2 (as opposed to O2 or H2O) remains challenging because of isobaric interference. Development of this new instrument will be based on close collaboration between stable isotope geochemists and laser spectroscopists from LSCE (Laboratoire des Sciences du Climat et de l'Environnement) and LIPhy (Laboratoire Interdisciplinaire de Physique). Building on our previous work and proof-of-concept experiments, we propose to build the first of a new generation of ultra-precise cavity ring-down spectrometers and to combine it with a custom dual-inlet system derived from existing IRMS devices. In order to attain the extreme precision levels quoted above, we plan to lock a DFB laser near 1.6~µm using optical feedback from a specially designed, ultra-stable "source cavity", resulting in a source with a very narrow linewidth around a highly stable center frequency, which will be injected in one or more ring-down cavities containing sample or reference gases. Design, assembly and initial testing will be performed at LIPhy, and the laser spectrometer will then be transferred to LSCE for accuracy tests, further optimizations, and initial geochemical applications. This process will take place in the context of a new PhD project which will include both instrumental development and early scientific applications, under dual LIPhy/LSCE supervision. As an added benefit, this will ensure a good transfer of theoretical and practical expertise from one lab to the other. By the end of this work, the instrument should be fully operational at LSCE, providing important new observations for paleo-climate and atmospheric studies. Technical advances from this project will provide a foundation for future implementations of this technique, and will certainly benefit a wide range of other laser spectrometric applications.

The ERC proposal BOREAS-STG19 was about winter cold-spells. The goal was to determine The (potential) changes in cold spells frequency/intensity due to anthropogenic forcing. Since they are notably difficult to determine because they rely on chaotic properties of the atmospheric circulation whose dynamics is high dimensional and turbulent, BOREAS-STG19 aimed at evaluating the role of thermodynamic vs dynamical components of these events from large to small spatial scales tracking energy exchanges in space, time and scale-space. The criticisms expressed by the PE10 panel focused on three aspects: i) the definition of cold-spell was misleading as BOREAS was focusing both on cold and snowy spells with the role of snowfall being unclear, ii) the usefulness of studying cold-spells in a context of warming climate was questioned, iii) the use of low dimensional models was questioned because their resolution is not adequate to represent small scales feedback for cold events. The BOREAS project submitted to the STG20 call addresses these issues by: i) focusing the project on snowstorms instead of cold spells, ii) showing evidence of the fact that the link between average warming and occurrence of snowstorms is far from being trivial, iii) substituting low dimensional climate models with state of the art convection permitting simulations, capable to provide a detailed representation of the physical processes leading to snowstorms. The abstract submitted to the STG20 call follows: “BOREAS assesses how climate change modify the frequency and intensity of snowstorms affecting European large populated areas in winter time. Anthropogenic emissions are responsible for temperature increase. Nonetheless, we still observe winter snowstorms. This apparent contradiction comes from the subtle effects of climate change on extreme events driven by the atmospheric circulation. Indeed, snowstorms are associated to extratropical cyclones which propagate in a southward– rather than eastward- direction as a result of the meandering of the mid-latitude jet-stream. In the present climate, the combination of higher surface winter temperatures with the advection of lower atmospheric cold air associated with those extratropical cyclones enhances evaporation and convective precipitations, often leading to more intense snowstorms than in the past. In a future climate it is unclear whether the effect of temperature increase will prevail on that of potential changes in the jet stream and convective feedback. BOREAS will clarify this by: 1) Tracking the changes in jet meandering amplitude in future emissions scenarios by projecting the jet dynamics in CMIP6 simulations on a subset of instantaneous indicators that track waviness, predictability and persistence of circulation patterns. This will assess the abundance of weather patterns possibly leading to snowstorms in the future. 2) Evaluating the capability of local convective feedback to enhance snowfalls despite increasing temperatures via a storyline approach based on simulations of past & present snowstorms with convection-permitting models, forced with future boundary conditions (e.g. higher sea-surface temperatures, different land-use & vegetation). Simulations will provide a comprehensive overview on future European snowstorms.” Based on these improvements, I request the ANR-Tremplin the funding to start the analysis of large scale drivers of snowstorms in existing climate simulations by evaluating the modifications in the tracks of extratropical cyclones travelling from polar regions to mid-latitudes in wintertime. The goal will be to assess changes in the frequency of polar extratropical cyclones travelling to mid-latitudes by evaluating the changes in the zonality of mid-latitude jet, projecting its dynamics on dynamical indicators and measuring shifts in waviness of mid-latitude patterns between present and future scenarios.

The H2020 call SC5-04-2017 « Towards a robust and comprehensive greenhouse gas verification system » will be opened on November 8 2016 and the deadline for the submission will be on March 7 2017. The present proposal requests support of the activities of the Laboratoire des Sciences du Climat et de l'Environnement (LSCE) for the preparation of a proposal to this call. The preparation is planned into three distinct phases: - Building the consortium, defining the general structure of the project, and hiring the services of a consultancy company (until June 2016) - Setting up the detailed structure of the project between June and September 2016 - Finalizing the proposal and adapting to the potential modifications of the call between November 2016 and February 2017. We feel that in order to properly address the H2020 call, and given its budget, a wide field of activities should be covered by our proposal. The proposal should thus be structured into a small number of components gathering several work packages. This would help define two level of interactions for the project coordination and highlight the logic of the proposal. A first meeting will be organized in Paris with a limited number (~20) of key potential partners with complementary expertise in the fields of the monitoring of the carbon and nitrogen stocks and land and anthropogenic fluxes, of operational systems for the earth observation, and of the set-up of Monitoring Reporting and Verification systems. This meeting and the subsequent interactions (mainly ours but also other involving the core team of the project) should lead to the selection of a first full list of the project partners by June 2016. In the meanwhile, we will try to hire the services of a consultancy company in order to support our coordination of the proposal. This service should be operational before June 2016. During the rest of the preparation of the proposal, we will stay strongly aware of the need to adapt to potential modifications of the H2020 call or to issues that could imply changes in the list of partners. The detailed structure of the project will be finalized by frequent interactions with the partners between June and September 2016. The PBS, list of tasks and their leads will be finalized and a preliminary text circulated among the partners by September 2016. The last phase will be the writing of the proposal in response to the call, relying on core partners identified to lead or co-lead different tasks, and receiving support from the consultancy company selected in the first phase.

This ANR application aims to support the application for an H2020 RIA project, PROCCOPE, that has already passed the first stage with optimal evaluations for the criteria used for this stage: "Excellence" and "Impacts". PROCCOPE stands for "PROcesses of Climate change: COnstraints from Past Events". If granted, the ANR-PROCCOPE will help 1/ consolidating our External Advisory Board and strengthening the links with the users of our research, 2/ obtain careful scientific proof-reading of the project so that we have the best chances to obtain the European funding. PROcesses of Climate change, COnstraints from Past Events, PROCCOPE, gathers experts in climate model development, in climate model applications, and in past climates and environments. Indeed physical (e.g. isotopes in ice cores) and environmental (e.g. lakes, vegetation) records of past climate states and transitions provide direct evidence about the role of key Earth system processes in climate and environmental changes. PROCCOPE will focus on the northern extratropics and the Arctic and will capitalize on well-documented climate changes in the past that are as large, and sometimes as fast, as those expected in the future. By exploiting the different sensitivities and temporal resolutions of the paleodata sources, PROCCOPE aims to elucidate the relative importance of specific atmospheric, oceanic, sea-ice, land surface and aerosol processes in different climate states, and the relationships between these states and short-term climate variability and extreme events. State-of-the-art models (CMIP5) simulate large-scale features of past climates reasonably well but are still unable to capture iconic regional features. PROCCOPE aims to identify the processes at stake in these model-data discrepancies, focus on them during the model developments, test new representations under present-day and radically different past climate states, in order to build improved climate models and more reliable climate projections. We propose a new methodology based on systematic model benchmarking against a large range of climate states and transitions and process oriented analyses. Our key objectives are: (a) proving that we can explain past climate and environmental changes in terms of key processes operating in the climate system, (b) identifying the key processes affecting climate model performance for a range of climate states and implementing them to improve the models used for climate projections, and (c) delivering improved knowledge and environmental models for impact studies.