Reliable quantification of the sources and sinks of greenhouse gases (GHGs), together with trends and uncertainties, is essential to monitoring the progress in mitigating anthropogenic emissions under the Paris Agreement.
Accurate estimation of GHG emissions and removals as an aid for decision-making by policy-makers at the national and European levels, and by regional authorities in Europe and other regions, will actively contribute to the international effort on GHG monitoring.
The current studies, will build on results from VERIFY project for the AFOLU sector described in detail by Petrescu et al., 2020 (https://essd.copernicus.org/articles/12/961/2020/), include GHG estimates from CO2 fossil and CO2 land from all sectors reported to UNFCCC, as well as GHG emissions from top-down approaches (inversions).
The data are derived from state-of-the-art bottom-up (BU) and top-down (TD) sources for the European Union and UK (EU27+UK). We integrate recent emission inventory data, process-based ecosystem model results, data-driven sector model results and inverse modelling estimates over the period 1990–2018. BU and TD products are compared with European National GHG Inventories (NGHGI) reported to the UN climate convention secretariat UNFCCC in 2019. Whenever available, we also report uncertainties, which in the NGHGIs are calculated based on ranges in observed (or estimated) emission factors and variability of activity data, using the error propagation method (95% confidence interval) or Monte-Carlo methods, and following clear guidelines (IPCC, 2006). There are no agreed-up guidelines to estimate uncertainties in TD or BU approaches. The uncertainties are usually assessed from the spread of different estimates within the same approach, though some groups or institutions report uncertainties for their estimates using a variety of methods, for instance, by varying parameters or input data. However, this gets complicated when dealing with complex process-based models when each individual run requires large amounts of computer time.
The main aim of these studies is to identify the issues which cause observed differences between NGHGI, BU and TD to further improve and build a pathway to a verification system. We found several main challenges in the comparison: the BU use of activity data, emission factor and emission allocation (in particular for CO2 fossil and CH4); very large NGHGI reported uncertainties which need to be reassessed (for N2O); and higher TD estimates than inventories (for both CH4 and N2O). We analyzed as well differences and inconsistencies between emissions, and made recommendations towards future actions to evaluate NGHGI data. While NGHGIs include uncertainty estimates, individual spatially disaggregated research datasets of emissions often lack quantification of uncertainty.
Currently, the following two syntheses are available in preprint version in ESSD:
The consolidated European synthesis of CO2 emissions and removals for EU27 and UK: 1990–2018
https://essd.copernicus.org/preprints/essd-2020-376/
The consolidated European synthesis of CH4 and N2O emissions for EU27 and UK: 1990–2018
https://essd.copernicus.org/preprints/essd-2020-367/
