The impact of policy and model uncertainties on emissions projections of the Paris Agreement pledges

Abstract

Tracking progress towards the Paris Agreement climate goal requires understanding the 2030 emission levels implied by countries’ National Determined Contributions (NDCs). However, key uncertainties and assumptions impact greenhouse gas (GHG) emission projections implied by the NDCs. This study analyses this impact, both globally and for major emitting countries. We find that the assessed uncertainties markedly affect global GHG emission projections. Full achievement of NDC targets is estimated to result in a range of 46-60 GtCO2eq by 2030 (median estimate: 53 GtCO2eq). The uncertainty in measuring historical emissions, including land-use, as reflected by different datasets is the most important contributing factor. This is followed by two equally important factors globally: socio-economic baseline uncertainty and uncertainty about the emissions implied by current policies in case NDCs are less ambitious than these. Overall, the impact of policy uncertainty (i.e. uncertainty resulting from conditionality of or ranges in NDC targets and uncertainty in emissions resulting from current policies) is about equally important as model/technical uncertainty (i.e. uncertainty in historical emissions and socio-economic baseline variations). This new insight is important for decision makers and researchers because a larger share of the total uncertainty is now attributable to aspects that can be influenced by policy decisions compared to previous analyses of NDC uncertainty.

Review of Sources of Uncertainty and Techniques Used in Uncertainty Quantification and Sensitivity Analysis to Estimate Greenhouse Gas Emissions from Ruminants

“…Accurate GHG inventories play an integral role in assessing sector contributions to emissions and formulating effective mitigation strategies [27,74,78]. However, uncertainties related to activity data and emission factors compromise the accuracy of these inventories, impacting climate change projections and mitigation policies [79,80]. Thus, continuous refinement in data collection methods, emission factor determinations, and overall inventory methodologies is essential for identifying, justifying, and adjudicating national-level mitigation commitments [74].…”

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“…3 The data comes from three model groups with updated NDCs, with cut-off dates ranging from November 2022 to September 2023 across studies den Elzen et al 2023;Meinshausen et al 2022; Note: Numbers in parentheses refer to the share of global GHG emissions from countries communicating NDCs with the characteristic shown in the first column. The last day of each COP is used as the cut-off date for each column, except for COP 28, for which the cut-off date is 25 September 2023.…”