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

==== 1.2.1.4 Resilience, Including Connections with Development Pathways and Transformation ====

<div id="h3-4-siblings" class="h3-siblings"></div>

'''Resilience''' in this report is defined as the capacity of social, economic and environmental systems to cope with a hazardous event or trend or disturbance, responding or reorganising in ways that maintain their essential function, identity and structure, while also maintaining the capacity for adaptation, learning and transformation (see Annex II: Glossary). Resilience is an entry point commonly used, although under a wide spectrum of meanings ( [[#Reghezza-Zitt--2012|Reghezza-Zitt et al., 2012]] ; [[#Flood--2014|Flood and Schechtman, 2014]] ; [[#Aldunce--2015|Aldunce et al., 2015]] ; [[#Tanner--2015|Tanner et al., 2015]] ; Fisichelli et al., 2016; Meerow et al., 2016; [[#Moser--2019a|Moser et al., 2019a]] ). Resilience as a system trait overlaps with concepts of vulnerability, adaptive capacity, and thereby risk. Resilience as a strategy overlaps with risk management, adaptation and also transformation ( [[#Woodruff--2018|Woodruff et al., 2018]] ; [[#Moser--2019a|Moser et al., 2019a]] ). Implemented adaptation is often organised around resilience as bouncing back and returning to a previous state after a disturbance (Fisichelli et al., 2016).

In much of the literature, resilience encompasses not just maintaining essential function, identity and structure, but also maintaining a capacity for adaptation, learning and transformation. Since the earliest framings of resilience around stability and persistence, ecology and allied fields have come to recognise that while systems are often persistent in the face of disturbance, disturbance also creates opportunity for transformation and the emergence of new pathways (Section 1.5.2; [[#Folke--2006|Folke, 2006]] ; [[#Allen--2010|Allen and Holling, 2010]] ; [[#Folke--2010|Folke et al., 2010]] ; [[#Gelcich--2010|Gelcich et al., 2010]] ; [[#Stockholm%20Resilience%20Center--2015|Stockholm Resilience Center, 2015]] ; [[#Doppelt--2017|Doppelt, 2017]] ). Across this literature, disturbance is framed as outside the system in question, for which the time frames and spatial scales of disturbances, impacts and responses are central to outcomes ( [[#Béné--2011|Béné et al., 2011]] ; [[#Brown--2014|Brown, 2014]] ; [[#Hamborg--2020|Hamborg et al., 2020]] ). Endogenous processes of transformation are presented as emergent, characterised by thresholds and, as a result, very difficult to anticipate ( [[#Scheffer--2001|Scheffer et al., 2001]] ; [[#Walker--2004|Walker and Meyers, 2004]] ; [[#Suding--2009|Suding and Hobbs, 2009]] ; [[#Scheffer--2012|Scheffer et al., 2012]] ; [[#Hughes--2013|Hughes et al., 2013]] ; [[#Scheffer--2015|Scheffer et al., 2015]] ). In the last 5 years (2016–2020), the concept of resilience has gained prominence as a core theme in the climate change adaptation literature ( [[#Nalau--2021|Nalau and Verrall, 2021]] ).

Often, development and adaptation communities of practice default to persistence and stability in their use of resilience ( [[#Cote--2012|Cote and Nightingale, 2012]] ; [[#MacKinnon--2013|MacKinnon and Derickson, 2013]] ). Such a framing aligns resilience with a long-standing but increasingly questioned belief that sustainable development can be achieved through incremental adjustments in behaviour and advances in technology that allow for the persistence of existing socioeconomic and socio-ecological arrangements ( [[#Klauer--1999|Klauer, 1999]] ; [[#Banerjee--2003|Banerjee, 2003]] ; [[#Redclift--2005|Redclift, 2005]] ; UN Inter-agency Task Force on Financing for Development 2019; Chapter 18, Section 1.5). However, the literature increasingly suggests that the achievement of sustainable development will require transformative change in socio-ecological systems at scales ranging from the community to the globe. The concept of climate resilient development, initially introduced in AR5 and now a key focus in this report (see Chapter 18), engages with such transformations and the associated questions of justice, power and politics as shaped by internal, endogenous social factors and their interactions with other drivers of change (Eriksen et al., 2015; [[#Nightingale--2015b|Nightingale, 2015b]] ; [[#Carr--2019|Carr, 2019]] ; [[#Nightingale--2019|Nightingale et al., 2019]] ; see also Chapter 18).

<div id="cross-chapter-box-climate" class="h2-container box-container"></div>

'''Cross-Chapter Box CLIMATE | Climate Reference Periods, Global Warming Levels and Common Climate Dimensions'''
<div id="h2-19-siblings" class="h2-siblings"></div>

Authors: Steven Rose (USA), Richard Betts (UK), Philippus Wester (Nepal/the Netherlands), Aris Koutroulis (Greece)

This Cross-Chapter Box sets out common climate dimensions to contextualise and facilitate AR6 WGII analyses, presentation, synthesis and communication of assessed, observed and projected climate change impacts across WGII chapters and cross-chapter papers. ‘Common climate dimensions’ are defined as common global warming levels (GWLs), time periods and levels of other variables, as needed by WGII authors for consistent communications. The set of climate variable ranges given below was derived from the AR6 WGI report and supporting resources, and helps to contextualise and inform the projection of potential future climate impacts and key risks. The information enables the mapping of climate variable levels to climate projections and vice versa, with ranges of results provided to characterise the physical uncertainties relevant to assessing climate impacts risk.

AR6 WGI Reference Periods, Climate Projections and Global Warming Levels

AR6 WGI adopts a common set of reference years and time periods to assess observed and projected climate change, namely the pre-industrial period, the current ‘modern’ period and future reference time periods. The IPCC Glossary (2021b) defines the pre-industrial period as ‘the multi-century period prior to the onset of large-scale industrial activity around 1750. The reference period 1850–1900 is used to approximate pre-industrial global mean surface temperature (GMST).’ The ‘modern’ period is defined as 1995 to 2014 in AR6, while three future reference periods are used for presenting climate change projections, namely near term (2021–2040), mid-term (2041–2060) and long term (2081–2100), in both the AR6 WGI and WGII reports. Importantly, the historical rate of warming assessed by WGI in AR6 is different to that assessed in AR5 and Special Report on Global Warming of 1.5°C (SR1.5, [[#IPCC--2018b|IPCC, 2018b]] ), due to methodological updates (see WGI Cross-Chapter Box 2.3 in [[IPCC:Wg2:Chapter:Chapter-2|Chapter 2]] for details (Gulev, 2021)). This means that the ‘modern’ period is assessed as slightly warmer compared to 1850–1900 than it would have been with AR5-era methods. This also has implications for the projected timing of reaching policy-relevant levels of global warming, which need to be understood.

To explore and investigate climate futures, climate change projections are developed using sets of different input projections. These consist of sets of projections of GHG emissions, aerosols or aerosol precursor emissions, land use change, and concentrations designed to facilitate evaluation of a large climate space and enable climate modelling experiments. For AR5 (and the Coupled Model Intercomparison Project (CMIP) 5 climate model experiments), the input projections were referred to as representative concentration pathways (RCPs). For AR6 (and the CMIP6 climate model experiments), new sets of inputs are used and referred to as SSP scenarios, where SSP refers to socioeconomic assumptions called the shared socioeconomic pathways (SSPs).

The RCPs are a set of four trajectories that span a large radiative forcing range, defined as increased energy input at surface level in Watts per square metre, ranging from 2.6 W m -2 (RCP2.6) to 8.5 W m -2 (RCP8.5) by the end of the 21st century, with RCP4.5 and RCP6.0 as intermediate scenarios, and RCP2.6 a peak and decline scenario reaching 3 W m -2 before 2100. A range of emissions scenarios compatible with each specific RCP was also assessed in AR5 ( [[#Ciais--2013|Ciais et al., 2013]] ).

A core set of five SSP scenarios, namely SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5, was selected in the AR6 WGI report to fill certain gaps identified in the RCPs (see WGI Cross-Chapter Box 1.4 in [https://www.ipcc.ch/report/ar6/wg2/chapter/chapter-1 Chapter 1] ( [[#Chen--2021|Chen et al., 2021]] )). The first number in the label is the particular set of socioeconomic assumptions driving the emissions and other climate forcing inputs taken up by climate models and the second number is the radiative forcing level reached in 2100. WG1 Cross-Chapter Box 1.4 in [https://www.ipcc.ch/report/ar6/wg2/chapter/chapter-1 Chapter 1] provides a comparison of this core set of SSP scenarios with scenarios used in previous reports, with SSP1–1.9 a low overshoot scenario consistent with limiting global average warming to 1.5°C, and SSP1-2.6 a scenario consistent with limiting warming to 2°C.

Also of importance to the impact literature and the WGII report are SSP-RCP combinations, that is, studies that employ climate outcomes based on RCPs and socio-economic assumptions based on SSPs. SSPs can be paired with a range of different RCPs because SSPs can be combined with mitigation policy assumptions to produce a range of emissions pathways. In addition to the SSPs, there are many other emissions pathways and societies consistent with any global mean temperature outcome. These represent uncertainty and broad ranges of possibilities that affect climate change exposure and vulnerability (Rose and and M. Scott, 2020; [[#Rose--2018|Rose and Scott, 2018]] ). Furthermore, there are large uncertainties in translating emissions scenarios into concentration pathways due to uncertainties in climate-carbon cycle feedbacks ( [[#Jones--2013|Jones et al., 2013]] ; [[#Booth--2017|Booth et al., 2017]] ).

The plausibility of emissions levels as high as the emissions scenario conventionally associated with the RCP8.5 and SSP5-8.5 concentration pathways has been called into question since AR5, as has the emissions pathway feasibility of the low scenarios ( [[#Hausfather--2020|Hausfather and Peters, 2020]] ; Rose and and Scott, 2020). However, these views are contested (Schwalm et al., 2020, for RCP8.5) It is important to realise that emissions scenarios and concentration pathways are not the same thing and higher concentration pathways, such as RCP8.5 could arise from lower emissions scenarios if carbon cycle feedbacks are stronger than assumed in the integrated assessment models (IAMs) used to create the standard scenarios ( [[#Booth--2017|Booth et al., 2017]] ). In the majority of full-complexity Earth System Models, these feedbacks are stronger than in the IAMs ( [[#Jones--2013|Jones et al., 2013]] ), so the RCP8.5 concentration pathway cannot be ruled out purely through consideration of the economic aspects of emissions scenarios. Nonetheless, the likelihood of a climate outcome, and the overall distribution of climate outcomes, are a function of the emissions scenario’s likelihood. Note that the original RCPs were created explicitly to facilitate a broad range of climate modelling experiments, with the expectation that other issues, such as socioeconomic uncertainty, could be subsequently explored ( [[#Moss--2010|Moss et al., 2010]] ).

<div id="_idContainer010" class="Box_Header-continued"></div>

Cross-Chapter Box CLIMATE1

An important feature of the AR6 cycle is a stronger emphasis on the use of future GWLs to support consistency and comparability across the three IPCC Working Groups’ contributions to the AR6 and improve communication. The common range of GWLs relative to the 1850 to 1900 period, termed the ‘Tier 1’ range by WGI, are 1.5, 2.0, 3.0 and 4.0°C. The use of GWLs assists in the comparison of climate states across climate change scenarios (projections) and in assessing the broader literature, as well as for cross-chapter and cross-working group comparisons. They facilitate the integration of climate projections, impacts, adaptation challenges and mitigation challenges within and across the three Working Groups as there is a close connection between the level of global warming and climate change impacts. Of particular interest is the timing of when the ‘Tier 1’ GWLs are reached, relative to the period 1850–1900, under the five SSP x–y scenarios, as well as RCP scenarios. For climate change impacts and adaptation responses, linking GWLs to RCP and SSP climate projections using a climate information translation resource is of great relevance for the WGII contribution to AR6.

<div id="_idContainer011" class="Box_Header-continued"></div>

Cross-Chapter Box CLIMATE1

AR6 WGII Common Climate Dimensions

WGII’s common climate dimensions include (a) a common range of GWLs from WGI, (b) common ranges for other climate variables, (c) information for translating climate variable levels to climate projections and vice versa. See Table Cross-Chapter Box CLIMATE.1 for global warming level ranges by time periods for RCP and SSP climate projections, and Table Cross-Chapter Box CLIMATE.2 for information regarding the timing for when GWLs are reached in climate projections. The common GWL range is based on WGI’s ‘Tier 1’ dimensions of integration range: 1.5°C, 2°C, 3°C and 4°C. The first table illustrates the greater levels of projected global warming with higher emissions pathways, as well as the increasing uncertainty in the climate response over time for a given pathway. The second table illustrates significant uncertainty in the timing for passing GWL thresholds which can narrow for a given GWL, the higher the emissions pathway. Finally, given the importance of geographic heterogeneity in projected changes in future climate, Table Cross-Chapter Box CLIMATE.3a and 3b are provided with ranges for select climate variables (temperature, precipitation, ocean) by GWL and continent (or ocean biome). The ranges illustrate spatial heterogeneity in potential physical changes in levels and uncertainty that are relevant to assessing climate impacts risk. There is significantly more spatial heterogeneity than represented in the table that is relevant to local decision makers (see, for instance, WGI Interactive Atlas).

The common climate dimensions can be used as a dimension of integration for impact studies in WGII, for example by providing a common framework for comparison of projected impacts for different studies (Figure Cross-Chapter Box CLIMATE.1). Moreover, GWL bands are needed in WGII to map the diverse temperature levels found across WGII’s literature. The GWL’s also facilitate integration with WGIII’s global emissions projections categorisation by global mean temperature (WGIII Chapter 3).

'''Table Cross-Chapter Box CLIMATE.1 |''' GWL ranges by time periods for CMIP5 (RCP) and CMIP6 (SSP) climate projections (20-year averages). Temperature anomalies relative to 1850–1900. Full ranges for CMIP raw results (across all models and ensemble runs) and WGI AR6 assessed ''very likely'' (5–95%) ranges. ''Sources: [[#hauser--2019|Hauser et al. (2019)]] ; WGI SPM ( [[#IPCC--2021a|IPCC, 2021a]] ); Table SPM.1''

{| class="wikitable"
|-
!
! colspan="9"| '''Full ranges'''

! colspan="9"| '''WGI AR6 assessed''' '''''very likely''''' '''(5–95%) ranges'''

|-
! '''Projection'''

! colspan="3"| '''2021–2040'''

! colspan="3"| '''2041–2060'''

! colspan="3"| '''2081–2100'''

! colspan="3"| '''2021–2040'''

! colspan="3"| '''2041–2060'''

! colspan="3"| '''2081–2100'''

|-
| RCP2.6

| 1.0

| to

| 2.2

| 1.0

| to

| 2.3

| 0.9

| to

| 2.3

| colspan="3"| n/a

| colspan="3"| n/a

| colspan="3"| n/a

|-
| RCP4.5

| 1.1

| to

| 2.2

| 1.4

| to

| 2.7

| 1.8

| to

| 3.3

| colspan="3"| n/a

| colspan="3"| n/a

| colspan="3"| n/a

|-
| RCP6.0

| 1.0

| to

| 2.0

| 1.3

| to

| 2.5

| 2.3

| to

| 3.6

| colspan="3"| n/a

| colspan="3"| n/a

| colspan="3"| n/a

|-
| RCP8.5

| 1.1

| to

| 2.6

| 1.7

| to

| 3.7

| 3.0

| to

| 6.2

| colspan="3"| n/a

| colspan="3"| n/a

| colspan="3"| n/a

|-
| SSP1–1.9

| 1.0

| to

| 2.4

| 1.1

| to

| 2.7

| 1.0

| to

| 2.5

| 1.2

| to

| 1.7

| 1.2

| to

| 2.0

| 1.0

| to

| 1.8

|-
| SSP1–2.6

| 1.0

| to

| 2.4

| 1.2

| to

| 2.9

| 1.3

| to

| 3.1

| 1.2

| to

| 1.8

| 1.3

| to

| 2.2

| 1.3

| to

| 2.4

|-
| SSP2–4.5

| 0.9

| to

| 2.5

| 1.3

| to

| 3.3

| 1.9

| to

| 4.4

| 1.2

| to

| 1.8

| 1.6

| to

| 2.5

| 2.1

| to

| 3.5

|-
| SSP3–7.0

| 1.0

| to

| 2.6

| 1.5

| to

| 3.7

| 2.7

| to

| 6.2

| 1.2

| to

| 1.8

| 1.7

| to

| 2.6

| 2.8

| to

| 4.6

|-
| SSP5–8.5

| 1.0

| to

| 2.7

| 1.6

| to

| 4.0

| 3.1

| to

| 7.2

| 1.3

| to

| 1.9

| 1.9

| to

| 3.0

| 3.3

| to

| 5.7

|}

'''Table Cross-Chapter Box CLIMATE.2 |''' '''Timing for when 20-year average GWLs are reached in CMIP5 (RCP) and CMIP6 (SSP) climate projections.''' GWL anomalies relative to 1850–1900. Ranges based on CMIP raw results (all models and ensemble runs), and WGI AR6 assessed results. For each GWL and RCP/SSP, the earliest and latest 20-year window when a 20-year average GWL is reached across the CMIP models and ensemble members is reported, or the ''very likely'' (5–95%) assessed range is reported. ‘n.c.’ means the GWL is not reached during the period 2021–2100. ''Sources: Hauser et al. (2019); WGI TS Cross-Section Box Table TS.1( [[#Arias--2021|Arias et al., 2021]] )''

[[File:9c8a83a119a2d5609fddb4d8e19beacb IPCC_AR6_WGII_Chapter1_Table_CCBOX_Climate2.png]]
'''Table Cross-Chapter Box CLIMATE.3a |''' '''Projected continental level result ranges for select temperature and precipitation climate change variables by global warming level.''' Ranges are 5 th and 95 th percentiles from SSP5–8.5 WGI CMIP6 ensemble results. There is little variation in the 5 th and 95 th percentile values by GWL across the SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5 projections. ''Source: WGI AR6 Interactive [https://www.ipcc.ch/chapter/atlas Atlas] ('' https://interactive-atlas.ipcc.Chapter/ '').''

[[File:fc9c7bb4af92e457044093883e993160 IPCC_AR6_WGII_Chapter1_Table_CCBOX_Climate3a.png]] [[File:80a4d420e4587568d68f4d4e70cd3eab IPCC_AR6_WGII_Chapter1_Table_CCBOX_Climate3a2.png]]
'''Table Cross-Chapter Box CLIMATE.3b |''' Projected sea surface temperature change ranges by global warming level and ocean biome (degrees Celsius). Ranges are 5 th and 95 th percentiles from SSP5–8.5 WGI CMIP6 ensemble results. There is little variation in the 5 th and 95 th percentile values by GWL across the SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5 projections. ''Source: WGI Interactive [https://www.ipcc.ch/chapter/atlas Atlas] ('' https://interactive-atlas.ipcc.Chapter/ '').''

[[File:13a9e86c2ed8802c6730a4a30d9d7812 IPCC_AR6_WGII_Chapter1_Table_CCBOX_Climate3b.png]]

[[File:82c391a6ad48701ee389482d8a417718 IPCC_AR6_WGII_Figure_1_Cross-Chapter_Box_CLIMATE_1.png]]

'''Figure Cross-Chapter Box CLIMATE.1 |''' '''Illustration of the use of global warming levels (GWLs) as a dimension of integration for impact studies: projected changes in river flows in major basins at 4°C global warming from four different multi-model ensembles.''' Results are shown for projected flow changes direct from Earth System Models (ESMs) in CMIP5 and CMIP6, for the Joint UK Land Environment Simulator (JULES) land surface model driven by meteorological outputs of the HadGEM3 and EC-Earth model in the High-End cLimate Impacts and eXtremes (HELIX) ensemble (Betts et al., 2018; Koutroulis et al., 2019), and nine hydrological models driven by a subset of five CMIP5 ESMs in the Inter-Sectoral Impacts Model Intercomparison Project (ISIMIP; Warszawski et al., 2014). Dots show results from individual models, blue for increased flows and red for decreased flows, black circles show the median for each ensemble, and black bars show the 95% confidence range in the median. See Figure 4.11 for further details.

To contextualise reported impacts by warming level for the influence of other determinants of risk, where appropriate and feasible (e.g., level of exposure/vulnerability, level of adaptation, time period), common time periods for the past and future can be aligned with WGI’s historical and projected time windows. Given differences in available literature, WGII chapters and CCPs (cross-chapter papers) contextualise impacts with respect to exposure, vulnerability and adaptation as appropriate.

Common ranges for other ‘climate’ variables, such as minimum and maximum temperatures and regional climates, are available based on WGI projections. They are based on feasible combinations with GWLs taken into consideration using the WGI Interactive Atlas. Climate information translation may have been necessary within chapters for mapping the WGII literature and assessments of the common climate dimensions. WGII’s climate impacts literature is based primarily on climate projections around AR5 and earlier or assumed temperature levels, though some recent impacts literature uses newer climate projections based on the CMIP6 exercise. Thus, it was important to be able to map climate variable levels to climate projections of different vintages and vice versa and adjust variables, when possible, to a common reference year. WGII chapters and CCPs only provide climate impact information for the common climate dimensions that their literature supports and where there is sufficient evidence.

Interpretation of the update in projected time of reaching 1.5°C global warming from SR1.5 to AR6

In an assessment using multiple lines of evidence, including models, observational constraints and improved understanding of climate sensitivity, WGI project a central estimate of the 20-year average warming crossing the 1.5°C GWL in the early 2030s in all scenarios assessed, except SSP5–8.5 ( [[#Lee--2021|Lee et al., 2021]] ). This is about 10 years earlier than the midpoint of the likely range (2030–2052) assessed in SR1.5, which assumed continuation of the observed warming rate reported at that time. However, this does not imply that the projected impacts of 1.5°C will be reached 10 years earlier, because roughly half of the 10-year difference is a result of updating the diagnosed historical rate of warming due to methodological advances, new datasets and other improvements ( [[#Gulev--2021|Gulev et al., 2021]] ). The other half of the 10-year difference arises because, for central estimates of climate sensitivity, most scenarios show stronger warming over the near term than was assessed as ‘current’ in SR1.5 ( ''medium confidence'' ).

The revised historical warming rate does not necessarily contribute to a change in timing of estimated impacts. It depends on how impacts are calculated relative to climate. Because the revised historical warming results in a redefinition of the 1.5°C GWL relative to the modern time period (1995–2014) rather than a different level of overall change (Figure Cross-Chapter Box CLIMATE.2 in Chapter 1), impacts assessed relative to the modern time period are unaffected. There are, in effect ‘old’ and ‘new’ definitions of the 1.5°C GWL with different levels of impacts, and the impacts assessed for the ‘old’ 1.5°C GWL now apply to a different level of global warming. However, the timing of impacts assessed relative to pre-industrial (e.g., aggregate economic impact estimates), are affected and we are closer to impact levels associated with 1.5°C and 2°C.

To illustrate with a worked example: in SR1.5, the historical warming between 1850–1900 and the modern period of 2006–2015 was assessed as 0.87°C, implying that the 1.5°C GWL would be accompanied by impacts associated with 0.63°C warming from the modern period. However, AR6 WGI ( [[#Gulev--2021|Gulev et al., 2021]] ) revised the assessment of warming between 1850–1900 and 2006–2015 to 0.94°C, implying that the 1.5°C GWL would be accompanied by a slightly lower level of impacts associated with only 0.56°C warming from the modern period. So, while the redefined 1.5°C GWL would be reached earlier, it would also be accompanied by a lower level of impacts (Figure Cross-Chapter Box CLIMATE.2 in Chapter 1). The impacts associated with the ‘old’ 1.5°C GWL would now be seen at 1.57°C global warming relative to 1850–1900, reached at the time of the ‘old’ 1.5°C GWL, if the same future level of warming were to be used as in SR1.5.

However, in addition to this redefinition of the historical warming rate, the assessed future warming in AR6 is also slightly faster than the continuation of reported recent warming used in SR1.5. This means that both the ‘old’ and ‘new’ 1.5°C GWLs are projected to be reached earlier than they would have been using the SR1.5 method. This and the revised historical warming diagnosis contribute approximately equally to the assessment of 1.5°C global warming being reached about 10 years earlier than projected in SR1.5.

Central estimates of impacts associated with a specifically defined 1.5°C GWL could therefore be considered to be projected to be reached approximately 5 years earlier than implied by SR1.5. However, uncertainties in regional climate responses at a given GWL are large (Cross-Chapter Box CLIMATE in Chapter 1, Table CLIMATE.3a) and natural climate variability occurs in parallel with ongoing warming, so the potential for impacts higher than central estimates could be a more urgent consideration for risk assessments and adaptation planning than the earlier projected timing of reaching 1.5°C ( ''high confidence'' ). It should also be noted that individual years may exceed 1.5°C above 1850–1900 sooner, but this is not the same as exceedance of the 1.5°C GWL which refers to the 20-year mean.

[[File:7e43102ea0d85ece597280d81e4b5c1c IPCC_AR6_WGII_Figure_1_Cross-Chapter_Box_CLIMATE_2.png]]

'''Figure Cross-Chapter Box CLIMATE.2 |''' '''Definitions of the 1''' '''.''' '''5°C global warming level (GWL) in SR1.5 ( [[#IPCC--2018b|IPCC, 2018b]] ) and AR6 WGI ( [[#IPCC--2021a|IPCC, 2021a]] ).''' GWLs are defined relative to 1850–1900 but impacts at the GWL are typically assessed in association with warming relative to a modern period 1995–2014, which in SR1.5 was 2006–2015. Revised assessment of the historical warming between 1850–1900 and the modern period (0.87°C in SR1.5 to 0.94°C in AR6) has the effect of slightly reducing the warming between the modern period and the 1.5°C GWL (0.63°C in SR1.5 to 0.56°C in AR6), and the impacts at the GWL previously defined as 1.5°C in SR1.5 now occur at 1.57°C global warming with the AR6 definition. Warming values are central estimates. Heights of the bars are not to scale.

<div id="1.2.2" class="h2-container"></div>

<span id="narratives-storylines-scenarios-and-pathways"></span>