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Atmospheric measurements in and around the UK allow us to evaluate greenhouse gas emission reports submitted to the United Nations Framework Convention on Climate Change (UNFCCC). This presentation will highlight some key results of this “top-down” capability, describe the value of top-down evaluation in the inventory process, and outline how some remaining challenges are being addressed. Case studies will be presented on fluorinated gases (F-gases) and methane. Measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and UK Deriving Emissions linked to Climate Change (DECC) network suggest that overall, F-gas emissions have been overestimated in the UK inventory. For compounds such as HFC-134a, used primarily in mobile air conditioning, our analysis of the inventory model identified a set of underlying assumptions that may have explained the discrepancy. Subsequently, the model was revised, such that the most recent inventory and top-down estimates are in closer agreement. For methane, measurements over the last decade (2012 – 2021), suggest a decline in emissions of 2-3% per year. This decline is approximately consistent with the inventory, a result that builds confidence in the UK’s reporting during this period. However, the decline reported over the previous two decades (1990 – 2012) cannot be reconciled with atmospheric data, which do not suggest a substantial change. To determine the reasons for any similar discrepancies between the UK’s emission reports and top-down estimates that may occur in the future, new techniques are being developed through the Detection and Attribution of Regional Emissions project (DARE-UK). Preliminary results will be presented of sector-level estimates for agricultural, fossil fuel and waste emissions, that are being derived by incorporating high-frequency methane isotopologue or ethane observations into methane flux inversions.
Topic : Theme 2: State of play in integrated approaches for advanced GHG emission estimates and the way forward to operational services.
Reference : T2-B10
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