Editing IPCC:AR6/WGI/Chapter-12 (section)

== 12.1 Framing ==

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Climate change is already resulting in significant societal and environmental impacts and will induce major socio-economic damages in the future (AR5 WGII). The society, at large, benefits from information related to climate change risks, which enables the development of options to protect lives, preserve nature, build resilience and prevent avoidable loss and damage. Climate change can also lead to beneficial conditions that can be taken into account in adaptation strategies.

'''This chapter assesses climate change information relevant for regional impact and for risk assessment. It complements other WGI chapters that focus on the physical processes determining changes in the climate system and on methods for estimating regional changes.'''

Impacts of climate change are driven not only by changes in climate conditions, but also by changes in exposure and vulnerability (Cross-Chapter Box 1.3). This chapter concentrates on drivers of impacts that are of climatic origin (see also the IPCC Special Report on Global Warming of 1.5°C (SR1.5, [[#IPCC--2018|IPCC, 2018]] ), and [[IPCC:Wg1:Chapter:Chapter-1#1.3.2|Section 1.3.2]] in this Report), referred to in WGI as ‘climatic impact-drivers’ (CIDs). CIDs are physical climate system conditions (e.g., means, events, extremes) that affect an element of society or ecosystems. Depending on system tolerance, CIDs and their changes can be detrimental, beneficial, neutral, or a mixture of each across interacting system elements and regions. However, this chapter largely focuses on drivers commonly connected to hazards, and adopts the IPCC risk framework (Cross-Chapter Box 1.3) since the main objective of the United Nations Framework Convention on Climate Change (UNFCCC) is to ‘prevent dangerous anthropogenic interference with the climate system’ (Article 2).

In some cases, risk assessments may require climate information beyond the CIDs identified in this chapter, with further impacts or risk modelling often driven by historical climate forcing datasets (e.g., [[#Ruane--2021|Ruane et al., 2021]] ) and full climate scenario time series (e.g., [[#Lange--2019|Lange, 2019]] ) produced using methods described in Chapter 10. [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-12 Chapter 12] focuses on the assessment of a finite number of drivers and how they are projected to evolve with climate change, in order to inform impact and risk assessments.

This chapter is new in IPCC WGI assessment reports, in that it represents a contribution to the ‘IPCC risk framework’. Within this framework, climate-related impacts and risks are determined through an interplay between the occurrence of climate hazards and their consequences depending on the exposure of the affected human or natural system and its vulnerability to the hazardous conditions. In Chapter 12, we are assessing climatic impact-drivers that could lead to hazards or to opportunities, from the literature and model results since AR5. This will particularly support the assessment of key risks related to climate change by WGII (Chapter 16). Despite the fact that impacts may also be induced by climate adaptation and mitigation policies themselves, as well as by socio-economic trends, changes in vulnerability or exposure, and external geophysical hazards such as volcanoes, the focus here is only on climatic impacts and risks induced by shifts in physical climate phenomena that directly influence human and ecological systems (Cross-chapter Box 1.3).

This chapter follows the terminology associated with the framing introduced in [[IPCC:Wg1:Chapter:Chapter-1|Chapter 1]] (Cross-Chapter Box 1.2) and as found in Annex VII: Glossary. The highlighted terms below are introduced and used extensively in this chapter:

* '''Indices for climatic impact-drivers:''' numerically computable indices using one or a combination of climate variables designed to measure the intensity of the climatic impact-driver, or the probability of exceedance of a threshold. For instance, an index of heat inducing human health stress is the Heat Index (HI) that combines temperature and relative humidity (e.g., [[#Burkart--2011|Burkart et al., 2011]] ; [[#Lin--2012|Lin et al., 2012]] ; [[#Kent--2014|Kent et al., 2014]] ) and is used by the NOAA for issuing heat warnings.
* '''Thresholds for climatic impact-drivers:''' an identified index value beyond which a climatic impact-driver interacts with vulnerability or exposure to create, increase or reduce an impact, risk or opportunity. Thresholds can be used to measure various aspects of the climatic impact-driver (magnitude or intensity, duration, frequency, timing, and spatial extent of threshold exceedance). For instance, a threshold of daily maximum temperature above 35°C is considered critical for maize pollination and production (e.g., [[#Schauberger--2017|Schauberger et al., 2017]] ; [[#Tesfaye--2017|Tesfaye et al., 2017]] ).

The approach adopted here is consistent with the UN Sendai Framework for Disaster Risk Reduction 2015–2030, which aims to face disaster consequences (including but not limited to climate disasters) and reduce risks in natural, managed and built environments ( [[#Aitsi-Selmi--2015|Aitsi-Selmi et al., 2015]] ; [[#UNISDR--2015|UNISDR, 2015]] ). The classification of climatic impact-drivers in this chapter is largely consistent with the classification of hazards used in the Sendai Framework. However, the UNISDR hazard list spans a wider range of hazards inducing damage to society, including hazards that are not directly related to climate (such as volcanoes and earthquakes), which are excluded from the assessment herein. Furthermore, the UNISDR classification of hazards does not include mean climatic conditions, which are also discussed as climatic impact-drivers in this chapter. The first priority mentioned in the Sendai Framework is understanding disaster risk as a necessary step for action. Facilitating such an understanding is a clear goal of this chapter.

The chapter adopts a regional perspective (continental regions as defined in [[IPCC:Wg1:Chapter:Chapter-1|Chapter 1]] and used in WGII; see Figure 1.18) on climatic impact-drivers to support decision-making across a wide audience of global and regional stakeholders in addition to governments (e.g., civil society organizations, public and private sectors, academia). While the focus here is on future changes, it also describes current levels and observed trends of CIDs as an important point of reference for informing adaptation strategies.

Figure 12.1 summarizes the rationale behind ( [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-12 Chapter 12] as the linkage (also referred to as a ‘handshake’) between WGI and WGII, illustrating how the changing profile of risk may be informed by an assessment of climatic impact-drivers, aligning WGI findings on physical climate change with WGII needs. The implementation of mitigation policy shifts may modulate hazard probability changes (i.e., by reducing emissions to limit global warming) as well as regional vulnerability and exposure. The assessment herein is organized around regional climatic impact-drivers, but also relates key indices and thresholds to increasing global drivers (such as mean surface warming) as a contribution to the assessment of ‘Reasons for Concern’ in WGII ( [[#O’Neill--2017|O’Neill et al., 2017]] ).

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[[File:de7878cae608d4dc4798f18863a826be IPCC_AR6_WGI_Figure_12_1.png]]

'''Figure 1''' '''2.1 |''' '''Schematic diagram showing the use of climate change information (AR6 WGI chapters) for typical impacts or risk assessment (AR6 WGII chapters) and the role of Chapter 12, via an illustration of the assessment of property damage or loss in a particular region when extreme sea level exceeds dike height.'''

The narrative of ( [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-12 Chapter 12] is illustrated in Figure 12.2. First, [[#12.2|Section 12.2]] defines a range of climatic impact-driver categories that are relevant for regional and sectoral impacts. Next, [[#12.3|Section 12.3]] identifies climatic impact-drivers and their relevant indices that are frequently used in the context of climate impacts in the WGII focus sectors (AR6 WGII Chapters 2–8). The assessment of changes in regional-scale climatic impact-drivers is then developed within [[#12.4|Section 12.4]] by continent, following the structure of the WGII assessment report regional chapters (AR6 WGII Chapters 9–15), and adding the polar regions, open/deep ocean and other specific zones corresponding to the WGII Cross-Chapter Papers. [[#12.5|Section 12.5]] then presents a global perspective (both bottom-up and top-down) on the change of regional climatic impact-drivers, including an assessment of the ‘emergence’ of climatic impact-drivers. [[#12.6|Section 12.6]] discusses how climate information is used in ‘climate services’, which encompasses a range of activities bridging climate science and its use for adaptation and mitigation decision-making (see also AR6 WGII Chapter 17). The chapter concludes with final remarks in [[#12.7|Section 12.7]] .

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'''Figure 1''' '''2.2 |''' '''Visual guide to Chapter 12.'''

The chapter includes two Cross-Chapter Boxes. Cross-Chapter Box 12.1 connects climatic impact-drivers to global climate drivers and levels of warming as an element of the ‘Reasons for Concern’ framework (AR6 WGII Chapter 16). An additional Cross-Chapter Box, including three case studies from Europe, Asia and Africa, describes how climate services draw upon and apply regional climate information to support stakeholder decisions (Cross-Chapter Box 12.2).

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