An assessment of the performance of scenarios against historical global emissions for IPCC reports

https://doi.org/10.1016/j.gloenvcha.2020.102199Get rights and content

Highlights

  • It is essential to reassess the relevance of emissions scenarios with with long-term developments regularly.

  • ‘IPCC scenarios’ did not systematically over-/underestimate historical global emissions.

  • Historical global emissions followed a medium–high emissions pathway well within scenarios ranges.

  • Most scenarios overestimated OECD but underestimated non-OECD CO2 and GDP growth.

  • Adjusting SSP-BL “non-biomass renewables” & “nuclear” may be relevant for future updates.

  • We find six overall periods of fast/slow CO2 growth (1960-2020), highlighting differences between long- vs. short-term evaluations.

Abstract

Long-term emissions scenarios have served as the primary basis for assessing future climate change and response strategies. Therefore, it is important to regularly reassess the relevance of emissions scenarios in light of changing global circumstances and compare them with long-term developments to determine if they are still plausible, considering the newest insights. Four scenario series, SA90, IS92, SRES, and RCP/SSP, were central in the scenario-based literature informing the five Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC) and the sixth assessment cycle. Here we analyze the historical trends of carbon dioxide (CO2) emissions from fossil fuel combustion and industry and emissions drivers between 1960 and 2017. We then compare the emission scenario series with historical trends for the period 1990–2017/2018. The results show that historical trends are quite consistent with medium scenarios in each series. As a result, they can be regarded as valid inputs for past and future analyses of climate change and impacts. Global CO2 emissions 1960–2018 (and 1990–2018) comprised six (and three) overall subperiods of emissions growth significantly higher and lower than average. Historically, CO2 emissions (in absolute numbers and growth rate) are tightly coupled with primary energy and indirectly with GDP. Global emissions generally followed a medium-high pathway, captured by “middle-of-the-road” scenario narratives in the earlier series, and by combinations of “global-sustainability” and “middle-of-the-road” narratives in the most recent series (SRES and SSP-baselines). Historical non-OECD trends were best captured by “rapid-growth” and “regional-competition” scenarios, while OECD trends were close to regional-sustainability and global-sustainability scenarios. Areas where the emissions scenarios captured the historical trends less well, are renewable and nuclear primary energy supply. The fact that the actual historical development is consistent with rapid-growth narratives in the non-OECD regions might have important implications for future greenhouse gas emissions and associated climatic change.

Section snippets

Introduction and background

Emissions scenarios form a key tool in the scenario-based literature, informing the Intergovernmental Panel on Climate Change’s (IPCC) assessments (IPCC, 1990, Moss et al., 2010). The history of IPCC assessment reports now covers several generations of emissions scenarios. These include the “1990 IPCC First Scientific Assessment” (SA90), (IPCC, 1990), the “1992 IPCC Scenarios” (IS92) (Leggett et al., 1992), and the 2000 “Special Report on Emissions Scenarios” (SRES) (Nakicenovic and Swart, 2000

Material and methods

We performed a detailed comparison of CO2 emissions and socioeconomic variables for all emission scenario sets used for assessments for IPCC Assessment Reports (from now on, emission scenarios will be mainly referred to as scenarios). We selected five key variables, i.e., CO2 from fossil fuel and industry, population, GDP, total, and fossil primary energy. The variables were chosen because they are key scenario results in all four sets. Developments in population, economic growth, and

Categorizing emissions scenarios: Assumptions underlying the sets

Storylines were developed for the SRES and additionally for the SSPs. The SA90 and IS92 assumptions and quantifications can effectively be related to specific, more extensive narrative descriptions of the later sets. Despite the two earliest sets having more simplified assumptions, we categorize all emission scenarios in five scenario-families based on storylines to compare scenarios across all four sets (Table 2).

The general storylines of the scenario-families do not necessarily reflect the

Discussion

Climate change extends far into the future, making emissions scenarios and associated development in emissions and drivers essential for a broad range of analyses of climatic change mitigation, impacts, and adaptation. Regular evaluations of these scenarios are crucial, as new information about technological and socioeconomic developments becomes available over time, and scenario methods and tools change (Allen, 2003, O’Neill and Schweizer, 2013, van Vuuren et al., 2010). This paper compares

Conclusions

Due to the high relevance of emission scenarios as input for future climate change analyses that informed and shaped IPCC assessments for 30 years, it is relevant to regularly reassess the scenarios to inform future scenario development and the policy debate. Focusing on key variables (CO2 from energy and industry, population, GDP, energy system characteristics), we have compared long-term historical developments of key socioeconomic drivers and greenhouse gas emissions and compared historical

CRediT authorship contribution statement

Jiesper Tristan Strandsbjerg Pedersen: Conceptualization, Formal analysis, Methodology, Writing - original draft, Software, Visualization, Project administration, Validation. Filipe Duarte Santos: Conceptualization, Resources, Supervision, Validation. Detlef Vuuren: Conceptualization, Methodology, Validation. Joyeeta Gupta: Supervision. Ricardo Encarnação Coelho: Investigation, Validation. Bruno A. Aparício: Software, Visualization. Rob Swart: Conceptualization, Methodology, Formal analysis,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

A special thanks to William Pepper (involved in IS92 and SRES developments) for a proof-reading paper review (including a valuable and low-cost language revision), and additionally, for scanning and putting a long lost IS92 report into circulation in the scientific community (available at ResearchGate). The authors would like to thank Paul Chakroff (University of Lisbon) for valuable language review and terminology support, and Andre Oliveira (Climate Change Impacts, Adaptation, and Modelling -

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