Editing IPCC:AR6/SR15/Chapter-4 (section)

== 4.5 Integration and Enabling Transformation ==

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=== 4.5.1 Assessing Feasibility of Options for Accelerated Transitions ===

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Chapter 2 shows that 1.5°C-consistent pathways involve rapid, global climate responses to reach net zero emissions by mid-century or earlier. Chapter 3 identifies climate change risks and impacts to which the world would need to adapt during these transitions and additional risks and impacts during potential 1.5°C overshoot pathways. The feasibility of these pathways is contingent upon systemic change (Section 4.3) and enabling conditions (Section 4.4), including policy packages. This section assesses the feasibility of options (technologies, actions and measures) that form part of global systems under transition that make up 1.5°C-consistent pathways.

Following the assessment framework developed in Chapter 1, economic and technological, institutional and socio-cultural, and environmental and geophysical feasibility are considered and applied to system transitions (Sections 4.3.1–4.3.4), overarching adaptation options (Section 4.3.5) and carbon dioxide removal (CDR) options (Section 4.3.7). This is done to assess the multidimensional feasibility of mitigation and adaptation options that have seen considerable development and change since AR5. In the case of adaptation, the assessed AR5 options are typically clustered. For example, all options related to energy infrastructure resilience, independently of the generation source, are categorized as ‘resilience of power infrastructure’.

Table 4.10 presents sets of indicators against which the multidimensional feasibility of individual adaptation options relevant to warming of 1.5°C, and mitigation options along 1.5°C-consistent pathways, is assessed.

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'''Table 4.10'''

Sets of indicators against which the feasibility of adaptation and mitigation options are assessed, for each feasibility dimensions. The options are discussed in Sections 4.3.1-4.3.5 and 4.3.7.

<!-- TABLE -->
{| class="wikitable"
|-
| Feasibility Dimensions
| Adaptation Indicators
| Mitigation Indicators
|-
| Economic
| Microeconomic viability
Macroeconomic viability

Socio-economic vulnerability reduction potential

Employment &amp; productivity enhancement potential

| Cost-effectiveness
Absence of distributional effects

Employment &amp; productivity enhancement potential

|-
| Technological
| Technical resource availability
Risks mitigation potential

| Technical scalability
Maturity

Simplicity

Absence of risk

|-
| Institutional
| Political acceptability
Legal &amp; regulatory feasibility

Institutional capacity &amp; administrative feasibility

Transparency &amp; accountability potential

| Political acceptability
Legal &amp; administrative feasibility

Institutional capacity

Transparency &amp; accountability potential

|-
| Socio-cultural
| Social co-benefits (health, education)
Socio-cultural acceptability

Social &amp; regional inclusiveness

Intergenerational equity

| Social co-benefits (health, education)
Public acceptance

Social &amp; regional inclusiveness

Intergenerational equity

Human capabilities

|-
| Environmental/Ecological
| Ecological capacity
Adaptive capacity/ resilience building potential

| Reduction of air pollution
Reduction of toxic waste

Reduction of water use

Improved biodiversity

|-
| Geophysical
| Physical feasibility
Land use change enhancement potential

Hazard risk reduction potential

| Physical feasibility (physical potentials)
Limited use of land

Limited use of scarce (geo)physical resources

Global spread

|}
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The feasibility assessment takes the following steps. First, each of the mitigation and adaptation options is assessed along the relevant indicators grouped around six feasibility dimensions: economic, technological, institutional, socio-cultural, environmental/ecological and geophysical. Three types of feasibility groupings were assessed from the underlying literature: first, if the indicator could block the feasibility of this option; second, if the indicator has neither a positive nor a negative effect on the feasibility of the option or the evidence is mixed; and third, if the indicator does not pose any barrier to the feasibility of this option. The full assessment of each option under each indicator, including the literature references on which the assessment is based, can be found in supplementary materials 4.SM.4.2 and 4.SM.4.3. When appropriate, it is indicated that there is no evidence (NE), limited evidence (LE) or that the indicator is not applicable to the option (NA).

Next, for each feasibility dimension and option, the overall feasibility for a given dimension is assessed as the mean of combined scores of the relevant underlying indicators and classified into ‘insignificant barriers’ (2.5 to 3), ‘mixed or moderate but still existent barriers’ (1.5 to 2.5) or ‘significant barriers’ (below 1.5) to feasibility. Indicators assessed as NA, LE or NE are not included in this overall assessment (see supplementary material 4.SM.4.1 for the averaging and weighing guidance).

The results are summarized in Table 4.11 (for mitigation options) and Table 4.12 (for adaptation options) for each of the six feasibility dimensions: where dark shading indicates few feasibility barriers; moderate shading indicates that there are mixed or moderate but still existent barriers, and light shading indicates that multiple barriers, in this dimension, may block implementation.

A three-step process of independent validation and discussion by authors was undertaken to make this assessment as robust as possible within the scope of this Special Report. It must, however, be recognized that this is an indicative assessment at global scale, and both policy and implementation at regional, national and local level would need to adapt and build on this knowledge, within the particular local context and constraints. Some contextual factors are indicated in the rightmost column in Tables 4.11 and 4.12.

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=== 4.5.2 Implementing Mitigation ===

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This section builds on the insights on mitigation options in Section 4.3, applies the assessment methodology along feasibility dimensions and indicators explained in Section 4.5.1, and synthesizes the assessment of the enabling conditions in Section 4.4.

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==== 4.5.2.1 Assessing mitigation options for limiting warming to 1.5˚C against feasibility dimensions ====

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An assessment of the degree to which examples of 1.5°C-relevant mitigation options face barriers to implementation, and on which contexts this depends, is summarized in Table 4.11. An explanation of the approach is given in Section 4.5.1 and in supplementary material 4.SM.4.1. Selected options were mapped onto system transitions and clustered through an iterative process of literature review, expert feedback, and responses to reviewer comments. The detailed assessment and the literature underpinning the assessment can be found in supplementary material 4.SM.4.2.

The feasibility framework in Cross-Chapter Box 3 in Chapter 1 highlights that the feasibility of mitigation and adaptation options depends on many factors. Many of those are captured in the indicators in Table 4.10, but many depend on the specific context in which an option features. This Special Report did not have the mandate, space or the literature base to undertake a regionally specific assessment. Hence the assessment is caveated as providing a broad indication of the likely global barriers, ignoring significant regional diversity. Regional and context-specific literature is also just emerging as is noted in the knowledge gaps section (Section 4.6). Nevertheless, in Table 4.11, an indicative attempt has been made to capture relevant contextual information. The ‘context’ column indicates which contextual factors may affect the feasibility of an option, including regional differences. For instance, solar irradiation in an area impacts the cost-effectiveness of solar photovoltaic energy, so solar irradiation is mentioned in this column.

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<span id="table-4.11"></span>
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'''Table 4.11'''

Feasibility assessment of examples of 1.5°C-relevant mitigation options, with dark shading signifying the absence of barriers in the feasibility dimension, moderate<br />
shading indicating that, on average, the dimension does not have a positive or negative effect on the feasibility of the option, or the evidence is mixed, and faint<br />
shading the presence of potentially blocking barriers. No shading means that the literature found was not sufficient to make an assessment. Evidence and agreement<br />
assessment is undertaken at the option level. The context column on the far right indicates how the assessment might change if contextual factors were different. For<br />
the methodology and literature basis, see supplementary material 4.SM.4.1 and 4.SM.4.2.

<span id="abbreviations-used"></span>
'''Abbreviations used:'''

Ec: Economic – Tec: Technological – Inst: Institutional – Soc: Socio-cultural – Env: Environmental/Ecological – Geo: Geophysical

<!-- TABLE -->
{| class="wikitable"
|-
! System
! Mitigation Option
! Evidence
! Agreement
! Ec
! Tec
! Inst
! Soc
! Env
! Geo
! Context
|-
| rowspan="6"| Energy System Transitions
| Wind energy (on-shore &amp; off-shore)
| Robust
| Medium
|
| Wind regime, economic status, space for wind farms, and the existence of a legal framework for independent power producers affect uptake; cost-effectiveness affected by incentive regime
|-
| Solar PV
| Robust
| High
|
| Cost-effectiveness affected by solar irradiation and incentive regime. Also enhanced by legal framework for independent power producers, which affects uptake
|-
| Bioenergy
| Robust
| Medium
|
| Depends on availability of biomass and land and the capability to manage sustainable land use. Distributional effects depend on the agrarian (or other) system used to produce feedstock
|-
| Electricity storage
| Robust
| High
|
| Batteries universal, but grid-flexible resources vary with area’s level of development
|-
| Power sector carbon dioxide capture and storage
| Robust
| High
|
| Varies with local CO <sub>2</sub> storage capacity, presence of legal framework, level of development and<br />
quality of public engagement
|-
| Nuclear energy
| Robust
| High
|
| Electricity market organization, legal framework, standardization &amp; know-how, country’s ‘democratic fabric’, institutional and technical capacity, and safety culture of public and private institutions
|-
| rowspan="4"| Land &amp; Ecosystem Transitions
| Reduced food wastage &amp; efficient food production
| Robust
| High
|
| Will depend on the combination of individual and institutional behaviour
|-
| Dietary shifts
| Medium
| High
|
| Depends on individual behaviour, education, cultural factors and institutional support
|-
| Sustainable intensification of agriculture
| Medium
| High
|
| Depends on development and deployment of new technologies
|-
| Ecosystems restoration
| Medium
| High
|
| Depends on location and institutional factors
|-
| rowspan="9"| Urban &amp; Infra structure System Transitions
| Land-use &amp; urban planning
| Robust
| Medium
|
| Varies with urban fabric, not geography or economy;<br />
requires capacitated local government and legitimate<br />
tenure system
|-
| Electric cars and buses
| Medium
| High
|
| Varies with degree of government intervention; requires capacity to retrofit “fuelling” stations
|-
| Sharing schemes
| Limited
| Medium
|
| Historic schemes universal, but new ones depend on ICT status; undermined by high crime and low levels of law enforcement
|-
| Public transport
| Robust
| Medium
|
| Depends on presence of existing ‘informal’ taxi systems, which may be more cost-effective and affordable than capital-intensive new build schemes, as well as (local) government capabilities
|-
| Non-motorized transport
| Robust
| High
|
| Viability rests on linkages with public transport, cultural factors, climate and geography
|-
| Aviation &amp; shipping
| Medium
|
| Varies with technology, governance and accountability
|-
| Smart grids
| Medium
|
| Varies with economic status and presence or quality of existing grid
|-
| Efficient appliances
| Medium
| High
|
| Adoption varies with economic status and policy<br />
framework
|-
| Low/zero-energy buildings
| Medium
| High
|
| Depends on size of existing building stock and growth of building stock
|-
| rowspan="4"| Industrial System Transitions
| Energy efficiency
| Robust
| High
|
| Potential and adoption depend on existing efficiency, energy prices and interest rates, as well as government incentives
|-
| Bio-based &amp; circularity
| Medium
|
| Faces barriers in terms of pressure on natural resources and biodiversity. Product substitution depends on market organization and government<br />
incentivization
|-
| Electrification &amp; hydrogen
| Medium
| High
|
| Depends on availability of large-scale, cheap, emission-free electricity (electrification, hydrogen) or CO <sub>2</sub> storage nearby (hydrogen). Manufacturers’ appetite to embrace disruptive innovations
|-
| Industrial carbon dioxide capture, utilization and storage
| Robust
| High
|
| High concentration of CO <sub>2</sub> in exhaust gas improve economic and technical feasibility of CCUS in industry. CO <sub>2</sub> storage or reuse possibilities
|-
| rowspan="5"| Carbon Dioxide Removal
| Bioenergy and carbon dioxide capture and storage
| Robust
| Medium
|
| Depends on biomass availability, CO <sub>2</sub> storage capacity, legal framework, economic status and social acceptance
|-
| Direct air carbon dioxide capture and storage
| Medium
|
| Depends on CO <sub>2</sub> -free energy, CO <sub>2</sub> storage capacity, legal framework, economic status and social acceptance
|-
| Afforestation &amp; reforestation
| Robust
| High
|
| Depends on location, mode of implementation, and economic and institutional factors
|-
| Soil carbon sequestration &amp; biochar
| Robust
| High
|
| Depends on location, soil properties, time span
|-
| Enhanced weathering
| Medium
| Low
|
| Depends on CO <sub>2</sub> -free energy, economic status and social acceptance
|}
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