This activity is expected to foster and enhance collaboration between the modelling and observing (satellite, ground-based, airborne) communities and advance towards an enhanced global and regional assessment of the methane sources and sinks from land and the ocean, their short and long-term evolution as well as the related natural and anthropogenic processes and impacts on atmospheric chemistry and dynamics and on Earth radiation budgets. The expected outcomes hereafter are complying with the recommendations formulated by the user community during the ESA ATMOS-2021 conference^[1].

Project results are expected to contribute to all of the following outcomes:

• A significant European effort to develop an enhanced methane assessment capacity including extensive advanced in situ data at multiscale and from multi-platforms, novel satellite observations, and enhanced modelling efforts to quantify and understand hotspots and background for natural and anthropogenic methane emissions with unprecedented resolution in space and time.
• An increased coordination of in-situ observations of methane emissions including enhancing communication and networking between the relevant observation communities.
• Enhanced science base in Europe to perform global and regional (European) scale high-resolution assessment of the methane sources and sinks in relevant environments, their short and long-term changes, the related natural and anthropogenic sources, and impacts on atmospheric chemistry and dynamics.
• Clear policy advice on current and future climate contributions of methane on global and regional (European) scale, including elaboration on effective mitigation options.
• Provision of a significant contribution to IPCC and related scientific efforts regarding reducing methane emission uncertainties similar to those of the Global Carbon Project^[2].
• Contribution to achieve the goals of the COP26 Glasgow agreement on methane emission reductions and to the EU methane strategy^[3].

The challenge of this topic is to further quantify and understand natural and anthropogenic methane emissions based on carefully selected European land sites and European sea sites with unprecedented resolution in space and time that should leverage the latest advances in observations from satellite, ground-based, and airborne, together with advances in reconciling inverse and bottom-up modelling approaches.

The proposal will address this challenge through:

• Deploying large coordinated in situ, ground-based and airborne observation monitoring campaigns over different Earth’s ecosystems (terrestrial, terrestrial-aquatic continuum, and marine sub-seafloor) and key anthropogenic sources (e.g. agriculture, waste, mining, oil and gas industry) with comparable and scalable measurement approaches.
• Running these campaigns during an extended period of time and planning them beyond the duration of the projects, building on existing measurement infrastructures and initiatives, in order to support the validation of satellite products, but as well to support the development of new and enhancement of existing models and data assimilation techniques.
• Evaluating temporal change in methane release over centuries at selected, relevant sites from existing long-time series.
• Advancing towards an integrated methane observing system (on “facility scale”) that capitalises on the latest advances in observations from satellite, in situ, ground-based remote sensing and airborne instruments as well as results from citizen observations.
• Advancing the capacity of models and data assimilation techniques, related to methane emissions through specifically exploiting novel medium and high-resolution satellite data (e.g. GHGSat, PRISMA, Sentinel-2, Landsat-8/9, Worldview-3).
• Delivering inverse modelling to separate methane sources and sinks and to attribute inverse modelling estimated fluxes to specific processes building on sufficient spatial resolution to identify the origin, for instance, of large local emissions.
• Advancing towards an enhanced spatially and temporary high-resolution global and regional assessment of the methane sources and sinks and its dynamics over time, the related natural and anthropogenic processes, and impacts on climate.

This topic is part of a coordination initiative between the European Space Agency (ESA) and the EC on Earth System Science. Under the EC-ESA Earth System Science Initiative, both institutions aim at coordinating efforts to support complementary collaborative projects, funded on the EC side through Horizon Europe, and on the ESA side through the ESA FutureEO programme as part of the ESA Atmosphere Science Cluster^[4] and relevant ESA activities related to the use of the TROPOMI and other relevant missions.

Proposals should address the collaboration with ongoing or future ESA Atmosphere Science Cluster projects, including those that will be funded through dedicated coordinated invitations to tender, and should towards this end include sufficient means and resources for effective coordination.

ESA will contribute to this effort by providing a dedicated Earth observation satellite scientific component to complement, collaborate and coordinate with this activity. In particular, ESA will contribute with dedicated set of complementary scientific activities with special focus on exploring and exploiting the new capabilities offered by TROPOMI in combination with other relevant European and international satellite missions including novel very high-resolution observations.

When dealing with models, actions should promote the highest standards of transparency and openness, as much as possible going well beyond documentation and extending to aspects such as assumptions, code and data that is managed in compliance with the FAIR principles^[5]. In particular, beneficiaries are strongly encouraged to publish results data in open access repositories and/or as annexes to publications. In addition, full openness of any new modules, models or tools developed from scratch or substantially improved with the use of EU funding is expected.

Projects should take into account, during their lifetime, relevant activities and initiatives for ensuring and improving the quality of scientific software and code, such as those resulting from projects funded under the topic HORIZON-INFRA-2023-EOSC-01-02 on the development of community-based approaches.

[1] https://atmos2021.esa.int/

[2] https://www.globalcarbonproject.org/

[3] https://ec.europa.eu/energy/sites/ener/files/eu_methane_strategy.pdf

[4] https://eo4society.esa.int/communities/scientists/esa-atmosphere-science-cluster/

[5] FAIR (Findable, Accessible, Interoperable, Reusable).