Preparation for a European capacity to monitor CO2 anthropogenic emissions

Topic description

Specific Challenge:

A recent expert report has assessed the need and opportunity for an independent European capacity for CO₂ anthropogenic emissions, which includes space-borne observation. It recommends stepwise approach to implement a requirement-driven integration of remote-sensing, in situ and modelling capabilities for an operational end-to-end system. While the report recognises the importance of other observing other GHGs contributing to global warming it focuses on closing specifically the gap of monitoring anthropogenic CO₂ emissions linked to the COP21 context. Also, as the use of satellite observations has been rather successful for CH₄ flux inversions in the past, the potential to monitor other GHGs in particular methane and carbon monoxide are to be investigated only as secondary mission objectives in this coordination and support action (CSA). It is noteworthy that designing a space-borne observation instrument for CO₂ anthropogenic emissions will largely benefit from lessons learnt in the context of the European Space Agency's Earth Explorer programme 8 with the Carbonsat exploratory mission.

The development, the implementation and eventually the operation of such a European capacity will need the involvement of various players, such as space agencies, operators of in-situ measurement stations and of numerical weather prediction, leading experts for modelling and data assimilation. In particular, it has to build on past activities of the European Space Agency (ESA) and will be coordinated with the ESA's on-going and future programmes. Initiating the establishment of this community while delivering first concrete elements is at the heart of this action to cluster all relevant existing competences within Europe on the CO₂ emissions topic and thus reach the critical mass required for addressing such a challenging endeavour.

Following the Copernicus Space Component Evolution Plan, the Commission has set up a CO₂ monitoring task force with two work packages addressing separate but interconnected tasks. The first work package (Task A co-convened by ESA and the Commission) is dealing with the Space Component (specifically: a CO₂ pre-operational mission), the second work package task (Task B convened by the Commission) is addressing the end-to-end operational emission monitoring system, including in addition inverse modelling, in-situ observation networks, and emission inventories. These activities will be conducted in full collaboration with ESA, EUMETSAT and ECMWF. As regards the interaction with the Task Force, the CSA is expected to act as an accompanying scientific and technical support to the CO₂ monitoring task force, which in turn will provide the necessary programmatic guidance.

To advance in a coordinated preparation of a mature European capacity there is need to bring together the key European stakeholders and competent entities which are engaged in activities that can answer the questions outlined below, have the ability to network with suitable research actors to fill the knowledge gaps, and have the required expertise to assess the needs for an end-to-end operational system, with due attention to potential international cooperation opportunities for tackling this global challenge.

Activities will encompass the coordination of ongoing efforts, include mutual identification of research and infrastructural gaps, and facilitate a cooperation of further research and development to be undertaken to reach sufficiently mature capacities for an operational integration as a subsequent step.

The following four areas need to be coordinated to prepare a suitable and operational European approach. To be adequate, the responses to these series of questions addressing engineering oriented issues should capitalize and benefit from basic research projects as available in the H2020 framework and ESA preparatory studies:

1. Reconciling top down and bottom up estimates

The combined use of both satellite and in-situ observations with advanced data assimilation techniques should offer the possibility to monitor the emissions of anthropogenic CO₂ and at the same time to better quantify the biogenic fluxes. However, satellite or surface measurements and different assimilation systems may currently deliver different estimates of sources and sinks of CO₂. There is thus a strong need to improve both the processing of satellite observations as well as the structure of the data assimilation systems (e.g., components, modelling framework), in particular when systems are conceived for implementation in an operational context like Copernicus. Empirical bias correction schemes have been designed for satellite observations to reconcile satellite versus in-situ flux estimates, but the origin of the inconsistencies is still debated: possible weaknesses of the chemistry transport models that link the two types of measurements, possible systematic errors of the retrieval algorithms or the high impact of biased prior information from external sources on the estimated fluxes are three causes that have been mentioned, among others. There is a need to reduce or even remove the empiricism from the processing chains for these measurements in order to increase their effective impact for carbon studies. Additionally, especially for flux estimates at national and sub-national scales, the transport model component of both the transport inversion schemes and the carbon cycle/Fossil Fuel data assimilation systems (CCDAS/FFDAS alike) needs to be improved, and more observational constraints need to be integrated in an objective way to separate fossil from biogenic fluxes and reduce uncertainty in the derived flux estimates.

Studies are to be undertaken, and ongoing efforts by participants are to be directed at reducing or even avoiding the need for satellite bias-correction schemes by proposing new methods (e.g., CCDAS as a physically-based filtering tool), new numerical experiments, and/or inter-comparison exercises, that allow identifying the origin of the above-mentioned biases, regardless their origin (measurements, physical equations, inputs to the physical equations, etc.). Proposals should also address current weaknesses of data assimilation systems with for instance the use of better transport model, improved model data fusion techniques or advanced surface flux descriptions.

2. Library of simulations for emissions and atmospheric transport

The development of an operational capacity for monitoring fossil CO₂ emissions needs to be based on a series of simulations of these emissions and atmospheric transport at the relevant spatial and temporal resolutions. The simulations should build upon actual inventory emissions derived from a catalogue of emission objects and uncertainties. These simulations should feature patterns representative of regions such as Europe benefiting from good bottom up data infrastructure reporting accurate inventories of emissions as well as other regions reporting less accurate but important contributions to the global CO₂ emissions. These simulations should be as realistic as possible that is, accounting for the natural CO₂ sinks and source fluxes, including cloud cover, atmospheric aerosol load and type and any other atmospheric contributions that could hinder the retrieval of atmospheric CO₂ content from space-borne sensors operating in the NIR and SWIR spectral domains.

Studies are to be undertaken, and ongoing efforts by participants are to be directed at providing series of simulation scenarios that could serve to adequately dimension a space mission, in particular as regards the spatial and temporal sampling that would be required to assess the fossil fuel emissions with a limited enough uncertainty to make it useful for policy makers.

3. Uncertainty trade-off for fossil fuel emissions

The adequate dimensioning of the ensemble of space-borne and in-situ observations to monitor fossil fuel CO₂ emission must be driven by requirements from policymakers in charge of assessing the impacts of international agreements that foresee the reduction of CO₂ emissions in the atmosphere. The monitoring of anthropogenic emissions from space-borne sensors involves inverse transport modelling methods together with source and sink process models that have intrinsic limits regarding the accuracies that can be reached. It is essential to assess these current limits, so that the likely emission uncertainties associated with ensemble CO₂ observations can be estimated reliably for a variety of spatial and temporal resolutions. The potential synergies between actual CO₂ emissions estimates based on physical measurements and those derived from inventories and statistics should be addressed as well in view of reducing the overall budget of emission uncertainties.

Studies are to be undertaken, and ongoing efforts by participants are to be directed evaluating the current state of affairs and the possible improvements that should issue from an enhanced space-borne and in-situ observation scenarios. These studies should

• be based on a few modelling scenarios capturing typical situations of CO₂ emissions and atmospheric transport and accounting for biogenic sources and sinks;
• consider different scenarios regarding the density, reliability and quality of the information available in-situ;
• establish metrics and methods to assess CO₂ emission uncertainties at the appropriate scales and time-space resolutions;
• outline a set of concrete protocols for undertaking future closure experiments between top down and bottom up emission datasets at a variety of scales.

4. Attributing CO₂ emissions from in-situ measurements

Physically-based estimates of fossil fuel CO₂ emissions using jointly transport and process models together with space-borne observations require dedicated in-situ observation networks to attribute the emissions to anthropogenic activities in contrast to natural sources. Several techniques are available to achieve this task including measurements of atmospheric CO and radiocarbon concentration measurements. The latter are critically dependent on in-situ sampling and, consequently, sampling protocols have to be established according to the spatial and temporal variability of the main emission sources and the required space-time resolution of the estimates. Sampling scenarios need to be elaborated which could optimally contribute to achieving the task.

Studies are to be undertaken, and ongoing efforts by participants are to evaluate the optimisation of in-situ network of radiocarbon measurements in the space-time dimension so that concurrent CO₂ observations from space-borne instruments can be fully exploited to derive accurate estimates of fossil fuel emissions. To this end, a family of typical emission scenarios representing local and regional scales processes have to be considered. These scenarios should feature a range of realistic cases and conditions that could be taken as representative of a larger ensemble of occurrences. The optimization of the sampling procedures should be based on generic techniques enabling to trace the sources and evolutions of the uncertainties in the assessment of the contributing fossil fuel emissions.

The Commission considers that a proposal requesting a contribution from the EU of EUR 3.5 million with a duration of two to three years would allow this specific challenge with its several components to be addressed appropriately. Nonetheless, this does not preclude submission and selection of a proposal requesting other amounts. It is intended to fund a single project coordinating the different activities listed above.

The proposal is expected to lay the mature foundation for an independent space-borne observation capacity for CO₂ in the context of Europe's Climate Change challenges. Coordination and networking efforts are expected to lay the foundation for the operational integration of all relevant European capacities as a subsequent step.

More specifically, the results are to:

• Make a significant contribution to addressing the unresolved issue of ground-based versus space derived estimates of CO₂ fluxes.
• Generate a large database of CO₂ sources, sinks and atmospheric transport processes to help dimensioning the various elements to develop an operational EU anthropogenic CO₂ emission monitoring capacity.
• Establish a set of requirements regarding the accuracy as well as spatial and temporal resolutions for anthropogenic CO₂ emissions estimates, such that the policymakers can be provided with reliable CO₂ emission trends to evaluate the impact of (I)NDCs.
• Shape the appropriate dimension and distribution of a surface network to separate biogenic from anthropogenic CO₂ emissions.