Editing IPCC:AR6/WGI/Chapter-1 (section)

==== 1.4.4.2 Storylines ====

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As societies are increasingly experiencing the impacts of climate change-related events, the climate science community is developing climate information tailored for particular regions and sectors. There is a growing focus on explaining and exploring complex physical chains of events or on predicting climate under various future socio-economic developments. Since AR5, ‘storylines’ or ‘narratives’ approaches have been used to better inform risk assessment and decision-making, to assist understanding of regional processes, and represent and communicate climate projection uncertainties more clearly. The aim is to help build a cohesive overall picture of potential climate change pathways that moves beyond the presentation of data and figures (Glossary; Fløttum and Gjerstad, 2017; [[#Moezzi--2017|Moezzi et al., 2017]] ; [[#Dessai--2018|Dessai et al., 2018]] ; T.G. [[#Shepherd--2018|]] [[#Shepherd--2018|Shepherd et al., 2018]] ).

In the broader IPCC context, the term ‘scenario storyline’ refers to a narrative description of one or more scenarios, highlighting their main characteristics, relationships between key driving forces and the dynamics of their evolution (e.g., emissions of short-lived climate forcers assessed in [[IPCC:Wg1:Chapter:Chapter-6|Chapter 6]] are driven by ‘scenario storylines’; see [[#1.6|Section 1.6]] ). The AR6 WGI is mainly concerned with ‘physical climate storylines’. A physical climate storyline is a self-consistent and plausible physical trajectory of the climate system, or a weather or climate event, on time scales from hours to multiple decades (T.G. [[#Shepherd--2018|]] [[#Shepherd--2018|Shepherd et al., 2018]] ). This approach can be used to constrain projected changes or specific events on specified explanatory elements such as projected changes of large-scale indicators (Box 10.2). For example, [[#Hazeleger--2015|Hazeleger et al. (2015)]] suggested using ‘tales of future weather’, blending numerical weather prediction with a climate projection to illustrate the potential behaviour of future high-impact events (also see [[#Hegdahl--2020|Hegdahl et al., 2020]] ). Several studies describe how possible large changes in atmospheric circulation would affect regional precipitation and other climate variables, and discuss the various climate drivers that could cause such a circulation response ( [[#James--2015|James et al., 2015]] ; [[#Zappa--2017|Zappa and Shepherd, 2017]] ; [[#Mindlin--2020|Mindlin et al., 2020]] ). Physical climate storylines can also help frame the causal factors of extreme weather events ( [[#Shepherd--2016|Shepherd, 2016]] ) and then be linked to event attribution (Section 11.2.2 and Cross-Working Group Box: Attribution).

Storyline approaches can be used to communicate and contextualize climate change information in the context of risk for policymakers and practitioners (Box 10.2; e.g., [[#de%20Bruijn--2016|de Bruijn et al., 2016]] ; [[#Dessai--2018|Dessai et al., 2018]] ; [[#Scott--2018|Scott et al., 2018]] ; [[#Jack--2020|Jack et al., 2020]] ). They can also help in assessing risks associated with LLHI events ( [[#Weitzman--2011|Weitzman, 2011]] ; [[#Sutton--2018|Sutton, 2018]] ), because they consider the ‘physically self-consistent unfolding of past events, or of plausible future events or pathways’ ( [[#Shepherd--2018|]] [[#Shepherd--2018|Shepherd et al., 2018]] ), which would be masked in a probabilistic approach. These aspects are important as the greatest risk need not be associated with the highest-likelihood outcome, and in fact will often be associated with low-likelihood outcomes. The storyline approach can also acknowledge that climate-relevant decisions in a risk-oriented framing will rarely be taken on the basis of physical climate change alone; instead, such decisions will normally take into account socio-economic factors as well ( [[#Shepherd--2019|Shepherd, 2019]] ).

In the AR6 WGIAssessment Report, these different storyline approaches are used in several places (see Table 1.1). [[IPCC:Wg1:Chapter:Chapter-4|Chapter 4]] uses a storyline approach to assess the upper tail of the distribution of global warming levels (the storylines of high global warming levels) and their manifestation in global patterns of temperature and precipitation changes. [[IPCC:Wg1:Chapter:Chapter-9|Chapter 9]] uses a storyline approach to examine the potential for, and early warning signals of, a high-end sea level scenario, in the context of deep uncertainty related to our current understanding of the physical processes that contribute to long-term sea level rise. [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-10 Chapter 10] assesses the use of physical climate storylines and narratives as a way to explore uncertainties in regional climate projections, and to link to the specific risk and decision context relevant to a user, for developing integrated and context-relevant regional climate change information. [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-11 Chapter 11] uses the term storyline in the framework of extreme event attribution. [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-12 Chapter 12] assesses the use of a storylines approach with narrative elements for communicating climate (change) information in the context of climate services (Cross-Chapter Box 12.2).

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