Negative emissions and international climate goals\u2014learning from and about mitigation scenarios

Jérôme Hilaire,Joeri Rogelj,Gregory F Nemet,Gunnar Luderer,Max W Callaghan,Maria Del Mar Zamora,Jan C Minx,Jae Edmonds

doi:10.1007/s10584-019-02516-4

Abstract

For aiming to keep global warming well-below 2 °C and pursue efforts to limit it to 1.5 °C, as set out in the Paris Agreement, a full-fledged assessment of negative emission technologies (NETs) that remove carbon dioxide from the atmosphere is crucial to inform science-based policy making. With the Paris Agreement in mind, we re-analyse available scenario evidence to understand the roles of NETs in 1.5 °C and 2 °C scenarios and, for the first time, link this to a systematic review of findings in the underlying literature. In line with previous research, we find that keeping warming below 1.5 °C requires a rapid large-scale deployment of NETs, while for 2 °C, we can still limit NET deployment substantially by ratcheting up near-term mitigation ambition. Most recent evidence stresses the importance of future socio-economic conditions in determining the flexibility of NET deployment and suggests opportunities for hedging technology risks by adopting portfolios of NETs. Importantly, our thematic review highlights that there is a much richer set of findings on NETs than commonly reflected upon both in scientific assessments and available reviews. In particular, beyond the common findings on NETs underpinned by dozens of studies around early scale-up, the changing shape of net emission pathways or greater flexibility in the timing of climate policies, there is a suite of “niche and emerging findings”, e.g. around innovation needs and rapid technological change, termination of NETs at the end of the twenty-first century or the impacts of climate change on the effectiveness of NETs that have not been widely appreciated. Future research needs to explore the role of climate damages on NET uptake, better understand the geophysical constraints of NET deployment (e.g. water, geological storage, climate feedbacks), and provide a more systematic assessment of NET portfolios in the context of sustainable development goals.

Highlights

Fast dwindling carbon budgets are stimulating a lively debate on the role of negative emission technologies (NETs1) for keeping warming below 1.5 °C and 2 °C, as illustrated by a growing number of scientific and policy discussions on the subject (Fuss et al 2014; Geden 2015; Lomax et al 2015; Gasser et al 2015; Anderson 2015; Lewis 2015; Williamson 2016; Anderson and Peters 2016; Lackner 2016; Field and Mach 2017; Parson 2017; Peters and Geden 2017; Geden and Löschel 2017; van Vuuren et al 2017; Obersteiner et al 2018; Scott and Geden 2018)
integrated assessment models (IAMs) have played a central role in expanding the research frontiers of NETs and helping to discover policy-relevant findings about these technologies
Qualitative evidence so far has not been adequately aggregated into a traceable and updatable body of knowledge and has been disconnected from reviews of quantitative evidence based on large scenario ensembles

Summary

Introduction

Fast dwindling carbon budgets are stimulating a lively debate on the role of negative emission technologies (NETs1) for keeping warming below 1.5 °C and 2 °C, as illustrated by a growing number of scientific and policy discussions on the subject (Fuss et al 2014; Geden 2015; Lomax et al 2015; Gasser et al 2015; Anderson 2015; Lewis 2015; Williamson 2016; Anderson and Peters 2016; Lackner 2016; Field and Mach 2017; Parson 2017; Peters and Geden 2017; Geden and Löschel 2017; van Vuuren et al 2017; Obersteiner et al 2018; Scott and Geden 2018). We argue and will show in this article that the lack of systematicity runs the risk of omitting important niche and newly emerging results To address these shortcomings with a view on the upcoming Sixth Assessment Report (AR6), we present here the first thematic review (Boyatzis 1998; Guest et al 2012) of the available scenario literature on NETs; provide a comprehensive, traceable and updatable synthetic table of all statements on NETs; and re-analyse the most important ones quantitatively. We contribute to the systematic assessment literature by developing and employing a computer-assisted method to review 138 studies on the subject in a comprehensive and transparent manner, allowing us to synthesize many qualitative findings We complement this analysis by connecting it to a summary of the available quantitative evidence. We close by providing a more comprehensive overview of the landscape of findings and discuss major open avenues for research

Main findings from the scenario literature

Discussion and outlook