Editing IPCC:AR6/WGIII/Chapter-2 (section)

== 2.1 Introduction ==

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As demonstrated by the contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (AR6 WGI) ( [[#IPCC--2021a|IPCC 2021a]] ), greenhouse gas [[#footnote-010|4]] (GHG) concentrations in the atmosphere and annual anthropogenic GHG emissions continue to grow and have reached a historic high, driven mainly by continued fossil fuels use ( [[#Jackson--2019|Jackson et al. 2019]] ; [[#Friedlingstein--2020|Friedlingstein et al. 2020]] ; [[#Peters--2020|Peters et al. 2020]] ). Unsurprisingly, a large volume of new literature has emerged since AR5 on the trends and underlying drivers of anthropogenic GHG emissions. This chapter provides a structured assessment of this new literature and establishes the most important thematic links to other chapters in this report.

While AR5 has mostly assessed GHG emissions trends and drivers between 1970 and 2010, this assessment focuses on the period 1990–2019 with the main emphasis on changes since 2010. Compared to [[IPCC:Wg3:Chapter:Chapter-5|Chapter 5]] in the contribution of WG III to AR5 (Blanco et al. 2014), the scope of the present chapter is broader. It presents the historical background of global progress in climate change mitigation for the rest of the report and serves as a starting point for the assessment of long-term as well as near- and medium-term mitigation pathways in Chapters 3 and 4, respectively. It also provides a systemic perspective on past emissions trends in different sectors of the economy (Chapters 6–12), and relates GHG emissions trends to past policies (Chapter 13) and observed technological development (Chapter 16). There is also a greater focus on the analysis of consumption-based sectoral emissions trends, empirical evidence of emissions consequences of behavioural choices and lifestyles, and the social aspects of mitigation (Chapter 5). Finally, a completely new section discusses the mitigation implications of existing and planned long-lived infrastructure and carbon lock-in.

Figure 2.1 presents the road map of this chapter. It is a simplified illustration of the causal chain driving emissions along the black arrows. It also highlights the most important linkages to other chapters in this volume (blue lines). The logic of the figure is that the main topic of this chapter is GHG emissions trends (discussed only in this chapter at such level of detail), hence they are at the top of the figure in grey-outlined boxes. The secondary theme is the drivers behind these trends, depicted in the second line of grey-outlined boxes. Four categories of drivers highlight key issues and guide readers to chapters in which more details are presented. Finally, in addition to their own motivations and objectives, climate and non-climate policies and measures shape the aspirations and activities of actors in the main driver categories, as shown in the grey-outlined box below.

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'''Figure 2.1''' '''|''' '''[https://www.ipcc.ch/report/ar6/wg3/chapter/chapter-2 Chapter 2] road map and linkages toother chapters.''' Black arrows show the causal chain driving emissions. Blue lines indicate key linkages to other chapters in this report.

Accordingly, the grey-outlined boxes at the top of Figure 2.1 show that the first part of the chapter presents GHG emissions from two main perspectives: their geographical locations; and the places where goods are consumed and services are utilised. A complicated chain of drivers underlie these emissions. They are linked across time, space, and various segments of the economy and society in complex non-linear relationships. Sections shown in the second row of grey-outlined boxes assess the latest literature and improve the understanding of the relative importance of these drivers in mitigating GHG emissions. A huge mass of physical capital embodying immense financial assets and potentially operating over a long lifetime produces vast GHG emissions. This long-lived infrastructure can be a significant hindrance to fast and deep reductions of emissions; it is therefore also shown as an important driver. A large range of economic, social, environmental, and other policies has been shaping these drivers of GHG emissions in the past and are anticipated to influence them in the future, as indicated by the grey-outlined policies box and its manifold linkages. As noted, blue lines show linkages of sections to other chapters that discuss these drivers and their operating mechanisms in detail.

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