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

== 12.2 Methodological Approach ==

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This section details the methodological approach followed in [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-12 Chapter 12] and discusses the underlying rationale for the assessments presented herein. Scientific literature on vulnerability, impacts, and adaptation (as typically asssessed in IPCC WGII) is examined to identify relevant climatic impact-drivers (CIDs) that contribute to sectoral risks and opportunities. Projected changes in corresponding CID indices are then derived from existing literature on changes in the physical climate system, results of other AR6 WGI chapters, and direct calculations based on climate projections from several model ensembles.

The classification of climatic impact-drivers, the ways that they change (e.g., their magnitude or intensity, duration, frequency, timing and spatial extent) is described in this section. It is emphasized that this chapter assesses literature relating only to physical climatic impact-drivers, not their impacts on human systems or the environment. Thus, here we do not consider indicators including exposure or vulnerability as assessed by WGII, although the selection of climatic impact-drivers is informed by literature feeding into WGII.

( [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-12 Chapter 12] assesses climate change information relevant for regional impact and for risk assessment in the seven main sectors corresponding to Chapters 2–8 of the WGII Assessment Report:

* Terrestrial and freshwater ecosystems and their services (WGII Chapter 2);
* Ocean and coastal ecosystems and their services (WGII Chapter 3);
* Water (WGII Chapter 4);
* Food, fibre and other ecosystem products (WGII Chapter 5);
* Cities, settlements and key infrastructure (WGII Chapter 6);
* Health, well-being and the changing structure of communities (WGII Chapter 7);
* Poverty, livelihoods and sustainable development (WGII Chapter 8).

Many of these sectors also include assets affected by climate change that are important for recreation and tourism, including elements of ecosystems services, health and well-being, communities, livelihoods and sustainable development (see also [[IPCC:Wg1:Chapter:Chapter-1|Chapter 1]] on the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), and the IPCC Special Report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems (SRCCL; [[#Hurlbert--2019|Hurlbert et al., 2019]] ; [[#IPCC--2019c|IPCC, 2019c]] )).

CIDs can be captured in seven main types: heat and cold; wet and dry; wind; snow and ice; coastal; oceanic and other. Table 12.1 provides an overview of the seven CID types and the CID categories associated with each type. The type ‘Other’ comprises additional CIDs that are not encompassed within the other six CID types, including air pollution weather (e.g., meteorological conditions that favour high concentrations of surface ozone, particulate matter or other air pollutants), near-surface atmospheric CO <sub>2</sub> concentrations, and mean radiation forcing at the surface (which are, for example, relevant for plant growth). Icebergs, fog and lightning are also noted in this chapter but are not broadly assessed across all subsections. In addition, there can be changes in impacts associated with earthquakes that interact with climate variables and climate change, such as liquefaction (e.g., [[#Yasuhara--2012|Yasuhara et al., 2012]] ) during earthquakes, or earthquakes caused by snow and water changes ( [[#Amos--2014|Amos et al., 2014]] ; [[#Johnson--2017|Johnson et al., 2017]] ), which are secondary effects on geophysical hazards that are not further assessed in this chapter. The characteristics and physical description of the climate phenomena or essential climate variables associated with each of these CID categories are assessed and described in previous Chapters 2–11 or ( [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-12 Chapter 12] directly as indicated in Table 12.1. The CID categories are further mapped on to different sectors in [[#12.3|Section 12.3]] (Table 12.2).

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'''Table 12.1''' '''|''' '''Overview of the main climatic impact-driver (CID) types and related CID categories with a short description and their link to other chapters where the underlying climatic phenomenon and its associated essential climate variables are assessed and described.'''

[[File:b7672d886a8cc3f775d9a4e026e8703d IPCC_AR6_WGI_Chapter12_Table_12_1_1.jpg]] [[File:4149f4573e388d02820d3e8757901264 IPCC_AR6_WGI_Chapter12_Table_12_1_2.jpg]]

Potential changes in the seasonality of CIDs or the length and characteristics of seasons (e.g., changes in growing season length or pollen season) are also important as they may shift the timing of many CIDs with broad implications for sectors and regional stakeholders ( [[#Wanders--2015|Wanders and Wada, 2015]] ; [[#Cassou--2016|Cassou and Cattiaux, 2016]] ; [[#Hansen--2016|Hansen and Sato, 2016]] ; [[#Brönnimann--2018|Brönnimann et al., 2018]] ; [[#Marelle--2018|Marelle et al., 2018]] ; [[#Unterberger--2018|Unterberger et al., 2018]] ; [[#Kuriqi--2020|Kuriqi et al., 2020]] ). Episodic CIDs characterize impact-relevant conditions persisting from short to long time frames but eventually returning to normal conditions.

In some situations, phenomena causing severe impacts go well beyond a single extreme event or a single climate variable, and can include interaction of climatic conditions, such as sea level rise and storm surge ( [[#Wahl--2015|Wahl et al., 2015]] ), precipitation in combination with strong winds ( [[#Martius--2016|Martius et al., 2016]] ) or flooding quickly followed by a heatwave (S.S.-Y. [[#Wang--2019|]] [[#Wang--2019|]] [[#Wang--2019|]] [[#Wang--2019|Wang et al., 2019]] ; see also [[IPCC:Wg1:Chapter:Chapter-10#10.5.2|Section 10.5.2.4]] ). Such compound events, particularly in the context of climate extremes, are assessed in [[IPCC:Wg1:Chapter:Chapter-11#11.8|Section 11.8]] . A combination of non-extreme climatic impact-drivers in time or space can also lead to severe impacts ( [[#Cutter--2018|Cutter, 2018]] ).

Several climatic impact-drivers are reliant on many factors beyond their associated primary climatic phenomenon. For example, river flooding is heavily dependent on river management and engineering and could also be affected by tidal water levels due to sea level rise and/or storm surge. Coastal flooding could be affected by coastal protection structures, port and harbour structures, as well as river flows (on inlet-interrupted coasts). Coastal erosion could be influenced by coastal protection measures as well as fluvial sediment supply to the coast. Furthermore, air pollution weather is not the only or dominant driver, for instance, of surface ozone pollution, but precursor emissions from anthropogenic sources can play a significant role (Section 6.5). [https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-12 Chapter 12] focuses only on the influence of the atmospheric, land and oceanic conditions associated with the climatic impact-drivers and the confidence in the direction of CID changes given here does not take into account existing or potential future adaptation measures, unless otherwise stated.

For each CID category there can be a range of indices that capture the sector- or application-relevant characteristics of a climatic impact-driver as described in Sections 12.3 and 12.4. Indices for climatic impact-drivers that are based on absolute or percentile thresholds (e.g., daily maximum temperature above 35°C) can be affected by biases in climate model simulations, such as local or regional deviations of a simulated climate variable from observed values ( [[#Sillmann--2014|Sillmann et al., 2014]] ; [[#Dosio--2016|Dosio, 2016]] ). Where sensible (i.e., where reliable observational data are available and a climate model that fits for the desired purpose), the output of climate model simulations can be bias-adjusted, potentially involving advanced methods to account for multiple variables and extreme value statistics as assessed in detail in Cross-Chapter Box 10.2. Yet, there is no general agreement about which bias adjustment methods to apply, as artefacts can arise both from the climate model and from the bias adjustment method, and the number of available methods has considerably grown in recent years (for a detailed discussion of available methods and their performance see Sections 10.3.1.3.2 and 10.3.3.7.2, and Cross-Chapter Box 10.2). The WGI Interactive [[IPCC:Wg1:Chapter:Atlas|Atlas]] illustrates original and bias-adjusted CIDs (see Atlas.1.4.5).

A global perspective on climatic impact-drivers is provided in [[#12.5.1|Section 12.5.1]] . [[#12.5.2|Section 12.5.2]] focuses on assessing evidence for the emergence ( [[IPCC:Wg1:Chapter:Chapter-1#1.4.2.2|Section 1.4.2.2]] ) of an anthropogenic climate change signal on the change in CIDs beyond natural climate variability, based on the literature assessed in other chapters and additional literature, at both global and regional scales. The process of generating user-relevant regional climate information in the context of co-production and climate services is assessed in Sections 10.5, 12.6, Box 10.2 and Cross-Chapter Boxes 10.3 and 12.2. Cross-Chapter Box 12.1 provides a global perspective on climatic impact-drivers related to their evolution for different GWLs ( [[IPCC:Wg1:Chapter:Chapter-1#1.6|Section 1.6]] ).

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