Ambiguity in pledges made to meet the goals of the Paris Agreement means that estimates of global greenhouse gas emissions by 2030 may vary by about 30% according to an analysis in Nature Communications. The study indicates that these uncertainties could be reduced by 10% by including some simple clarifications to improve the interpretation of nationally determined contributions (NDCs) pledged by individual countries.
To assess the progress towards achieving the Paris Agreement climate goals a stock-taking exercise is required, which involves countries submitting their climate plans, or NDCs, every five years. The NDCs cover aspects as diverse as mitigation efforts and issues with implementation, so their interpretation is ambiguous. This has led to uncertainty in future emissions projections with implications for achieving the temperature targets set out by the Paris Agreement (which aims to limit warming to below 2 degrees C).
Joeri Rogelj and colleagues use an integrated assessment modelling framework to estimate the implied greenhouse gas emissions under the current NDCs. They find that uncertainty in global emissions varies by -10% to +20% around a median estimate of 52 gigatonnes of equivalent CO2 per year in 2030. These uncertainties come from assumptions of socioeconomic development, and to a lesser extent, formulation of the NDC targets and variations in alternative energy accounting methods. The overall range of emissions could be reduced by 10% by simple technical clarifications, but other uncertainties are a result of political choices and are harder to reduce.
The chance of limiting long-term global warming to either 1.5 degrees C or 2 degrees C varies strongly as a function of the emissions uncertainty range in 2030; this analysis suggest actions that could facilitate the effective implementation of the Paris Agreement.
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