The UN Paris Agreement includes a legally binding mechanism to increase climate mitigation action over time. Countries put forward pledges known as nationally determined contributions (NDCs) whose impact is assessed in regular global stock taking exercises. This allows actions towards climate objectives to be strengthened. However, the actions set out in the NDCs are described ambiguously which introduces uncertainty into the stocktaking process and presents a danger that action plans will not be strengthened sufficiently to avoid dangerous levels of climate change.
The table shows how potential contributors affect uncertainty in projections of global greenhouse gas emissions for the year 2030.
The current ambiguity in NDCs is a critical issue for the global stocktake. Depending on the interpretation of these action plans, the IIASA research shows that emissions could either continue to increase, stabilize, or decrease by 2030.
Range of 2030 emissions resulting from various interpretations of the current NDCs. Global historical emissions and projected emissions under the current NDCs. Figure reproduced from Rogelj et al., Nature Communications (2017). Interpretations of the various “SSP” scenarios are provided in Riahi et al. (2018).
The Paris Agreement however aims for emissions to peak as soon as possible. Even with the great uncertainty about the effect of climate change mitigation plans the world is definitely not on track to limit warming to below 2°C, let alone 1.5°C. Unless policymakers strengthen their nationally defined contributions to reduce uncertainties the choices to be made beyond 2030 become starkly unpalatable. For example, a sudden increase in carbon prices in 2030 (by a factor of about four) is to be anticipated and the window on limiting warming to 1.5°C would close.
Regional contributions to overall NDC emission projection uncertainty. (a) Regional emissions contributions to global emissions and uncertainty under the full implementation of current NDCs. Shadings show the minimum–maximum range of emissions estimates per region; (b) Estimates of the magnitude of uncertainty induced in 2030 per source relative to the median estimate; (c) Average contribution to the full uncertainty range in 2030 per uncertainty source with the 10 most important contributions identified by region; (d) As b but per geographical region. AFR, SubSaharan Africa; CPA, Centrally Planned Asia and China; EEU, Central and Eastern Europe; FSU, Former Soviet Union; LAM, Latin America and the Caribbean; MEA, Middle East and North Africa; NAM, North America; PAS, Pacific OECD; SAS, South Asia; PAS, Other Pacific Asia; WEU,Western Europe. Country borders use the simplified TM World borders, provided by Bjorn Sandvik (thematicmapping.org). Figure reproduced from Rogelj et al., Nature Communications (2017).
Some variation can easily be removed from emissions targets by technical clarifications but others depend on government policy choices and assumptions for which there is no simple technical fix. IIASA researchers studied the actions pledged by each country to reduce greenhouse gas emissions. From six potential contributors several were identified that contribute significantly to overall uncertainty around reaching the targets of the Paris Agreement.
IIASA Policy Briefs present the latest research for policymakers from IIASA - an international, interdisciplinary research institute with National Member Organizations (NMOs) in countries in Africa, the Americas, Asia, and Europe. The views expressed herein are those of the researchers and not necessarily those of IIASA or its NMOs.
Last edited: 26 June 2019
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Rogelj J ORCID: https://orcid.org/0000-0003-2056-9061, Fricko O ORCID: https://orcid.org/0000-0002-6835-9883, Meinshausen M, Krey V ORCID: https://orcid.org/0000-0003-0307-3515, Zilliacus JJJ, & Riahi K ORCID: https://orcid.org/0000-0001-7193-3498 (2017). Understanding the origin of Paris Agreement emission uncertainties. Nature Communications 8: e15748. DOI:10.1038/ncomms15748.
References and useful resources
Gütschow J, Jeffery L, Gieseke R, Gebel R, Stevens D, Krapp M, & Rocha M (2016). The PRIMAP-hist national historical emissions time series (1850-2014). doi.org/10.5880/PIK.2016.003, GFZ Data Services.
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