Abstract
Abstract. Since the first estimate of global CO2 emissions was published in 1894, important progress has been made in the development of estimation methods while the number of available datasets has grown. The existence of parallel efforts should lead to improved accuracy and understanding of emissions estimates, but there remains significant deviation between estimates and relatively poor understanding of the reasons for this. Here I describe the most important global emissions datasets available today and – by way of global, large-emitter, and case examples – quantitatively compare their estimates, exploring the reasons for differences. In many cases differences in emissions come down to differences in system boundaries: which emissions sources are included and which are omitted. With minimal work in harmonising these system boundaries across datasets, the range of estimates of global emissions drops to 5 %, and further work on harmonisation would likely result in an even lower range, without changing the data. Some potential errors were found, and some discrepancies remain unexplained, but it is shown to be inappropriate to conclude that uncertainty in emissions is high simply because estimates exhibit a wide range. While “true” emissions cannot be known, by comparing different datasets methodically, differences that result from system boundaries and allocation approaches can be highlighted and set aside to enable identification of true differences, and potential errors. This must be an important way forward in improving global datasets of CO2 emissions. Data used to generate Figs. 3–18 are available at https://doi.org/10.5281/zenodo.3687042 (Andrew, 2020).
Highlights
Since the first known estimate of global anthropogenic emissions of CO2 was made in the early 1890s, methods have substantially improved, detail has increased, and additional emissions sources have been included
This paper summarises early efforts to quantify global CO2 emissions, before moving to current datasets, starting by discussing differences that can be expected a priori, describing the important Intergovernmental Panel on Climate Change (IPCC) inventory guidelines, summarising the publicly available emissions datasets, and comparing these in some detail and explaining quantitative differences where possible
Since 1996, Annex I parties to the UN Framework Convention on Climate Change (UNFCCC) have been required to submit emissions inventories for at least the period from 1990 to 2 years before the submission year, following a decision made at the first Conference of the Parties (COP) (UNFCCC, 1995)
Summary
Since the first known estimate of global anthropogenic emissions of CO2 was made in the early 1890s, methods have substantially improved, detail has increased, and additional emissions sources have been included. This paper summarises early efforts to quantify global CO2 emissions, before moving to current datasets, starting by discussing differences that can be expected a priori, describing the important IPCC inventory guidelines, summarising the publicly available emissions datasets, and comparing these in some detail and explaining quantitative differences where possible Because many of these products have appeared and will continue to appear in Earth System Science Data, readers can apply this review as a detailed guide to most recent emissions compilations and products as published in this journal
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