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

== 12.1 Introduction ==

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=== 12.1.1 Chapter Overview ===

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The scope of this chapter was motivated by the need for a succinct bottom-up cross-sectoral view of greenhouse gas (GHG) emissions mitigation coupled with the desire to provide systemic perspectives on critical mitigation potentials and options that go beyond individual sectors and cover cross-sectoral topics such as food systems, land systems, and carbon dioxide removal (CDR) methods. Driven by this motivation, Chapter 12 provides a focused thematic assessment of CDR methods and food systems, followed by consideration of land-related impacts of mitigation options (land-based CDR and other mitigation options that occupy land) and other cross-sectoral impacts of mitigation, with emphasis on synergies and trade-offs between mitigation options, and between mitigation and other environmental and socio-economic objectives. The systems focus is unique to the Sixth Assessment Report (AR6) of the IPCC and is of critical policy relevance as it informs coordinated approaches to planning interventions that deliver multiple benefits and minimise trade-offs, and coordinated policy approaches to support such planning, to tap relatively under-explored areas for the strengthening and acceleration of mitigation efforts in the short to medium term, and for dealing with residual emissions in hard-to-transition sectors in the medium to long term.

Table 12.1 presents an overview of the cross-sectoral perspectives addressed in Chapter 12, mapping the chapter’s main themes to the sectoral and global chapters in this report. These mappings reflect the cross-sectoral aspects of mitigation options in the context of sustainable development, sectoral policy interactions, governance, implications in terms of international trade, spillover effects, and competitiveness, and cross-sectoral financing options for mitigation. While some cross-sector technologies are covered in more detail in sectoral chapters, this chapter covers important cross-sectoral linkages and provides synthesis concerning costs and potentials of mitigation options, and co-benefits and trade-offs that can be associated with deployment of mitigation options. Additionally, Chapter 12 covers CDR methods and specific considerations related to land use and food systems, complementing Chapter 7. The literature assessed in the chapter includes both peer-reviewed and grey literature since the Fifth Assessment Report (AR5) of the IPCC, including the IPCC Special Report on Global Warming of 1.5°C (SR1.5), the IPCC Special Report on Climate Change and Land (SRCCL) and the IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC). Knowledge gaps are identified and reflected where encountered, as well as in a separate section. Finally, a strong link is maintained with sectoral chapters and the relevant global chapters of this report to ensure consistency.

'''Table 12.1 | An overview of cross-sector perspectives addressed''' '''in Chapter 12.'''

{| class="wikitable"
|-
!
! colspan="7"| Sectoral chapters

! colspan="5"| Global chapters

|-
| '''Chapter 12 themes'''

| '''Chapter 5'''

| '''Chapter 6'''

| '''Chapter 7'''

| '''Chapter 8'''

| '''Chapter 9'''

| '''Chapter 10'''

| '''Chapter 11'''

| '''Chapter 13'''

| '''Chapter 14'''

| '''Chapter 15'''

| '''Chapter 16'''

| '''Chapter 17'''

|-
| '''Costs &amp; potentials'''

| Change in demand

| Renewables

CCU

CCS

Nuclear

| Land-use change

| Urban planning

Cities

Demographics

| Standards

Electrification

| Hybridisation

Electric vehicles

Fuel economy

Decoupling

| Technology

Biomass

CCU

CCS

| Enabling of mitigation

|
| Finance of mitigation

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| Synergies and trade-offs with SDGs

|-
| '''CDR'''

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| BECCS

| Land-based CDR

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| Carbon storage in buildings

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| International governance

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| '''Food systems'''

| Food demand

Well-being

| Energy demand of some emerging mitigation options

| Agricultural production

Demand-side measures

| Urban food systems; controlled-environment agriculture

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| Food transport

| Food processing and packaging

| Food system transformation

| Governance

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| Food system and SDGs

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| '''Mitigation &amp; land use'''

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| Land use/ occupation: bioenergy hydro solar windnuclear

| A/R Biomass production

Bioenergy

Biochar

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| Land use and biomass supply

| Land use and biomass supply

| Land use and biomass supply

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| Governance

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| Co-benefits and adverse side effects

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| '''Cross-sectoral perspectives'''

| colspan="7"| Electrification, Hydrogen, Digitalisation, Circularity, Synergies, Trade-offs, Spillovers

| Policy interactions

Policy packages

Case studies Value chain and carbon leakage

| Governance

Leakage

| Blended financing

| General-urpose technologies Electrification Hydrogen

| SDGs co-benefits

Trade-offs

Adaptation

|}

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=== 12.1.2 Chapter Content ===

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Chapters 5 to 11 assess outcomes from mitigation measures that are applicable in individual sectors, and potential co-benefits and adverse side effects of these individual measures. Chapter 12 brings together the cross-sectoral aspects of these assessments including synergies and trade-offs as well as the implications of measures that have application in more than one sector and measures whose implementation in one sector impacts implementation in other sectors.

Taking stock of the sectoral mitigation assessments, Chapter 12 provides a summary synthesis of sectoral mitigation costs and potentials in the short and long term along with comparison to the top-down integrated assessment model (IAM) assessment literature of [[IPCC:Wg3:Chapter:Chapter-3|Chapter 3]] and the national/regional assessment literature of Chapter 4.

In the context of cross-sectoral synergies and trade-offs, the chapter identifies a number of mitigation measures that have application in more than one sector. Examples include measures involving product and material circularity, which contribute to mitigation of GHG emissions in a number of ways, such as treatment of organic waste to reduce methane emissions, avoid emissions through generation of renewable energy, and reduce emissions through substitution of synthetic fertilisers. Low-carbon energy technologies such as solar and wind may be used for grid electricity supply, as embedded generation in the buildings sector (e.g., rooftop solar) and for energy supply in the agriculture sector. Nuclear and bio-based thermal electric generation can provide multiple synergies including base load to augment solar and wind, district heating, and seawater desalination. Grid-integrated hydrogen systems can buffer variability of solar and wind power and are being explored as a mitigation option in the transport and industry sectors. Carbon capture and storage (CCS) has potential application in a number of industrial processes (cement, iron and steel, petroleum refining and pulp and paper) and the fossil fuel electricity sector. When coupled with energy recovery from biomass (BECCS), CCS can help to provide CO 2 removal from the atmosphere. On the demand side, electric vehicles are also considered an option for balancing variable power, energy efficiency options find application across the sectors, as does reducing demand for goods and services, and improving material use efficiency. Focused inquiry into these areas of cross-sectoral perspectives is provided for CDR, food systems, and land-based mitigation options.

A range of examples of where mitigation measures result in cross-sectoral interactions and integration is identified. The mitigation potential of electric vehicles, including plug-in hybrids, is linked to the extent of decarbonisation of the electricity grid, as well as to the liquid fuel supply emissions profile. Making buildings energy positive, where excess energy is used to charge vehicles, can increase the potential of electric and hybrid vehicles. Advanced process control and process optimisation in industry can reduce energy demand and material inputs, which in turn can reduce emissions linked to resource extraction and manufacturing. Trees and green roofs planted to counter urban heat islands reduce the demand for energy for air conditioning and simultaneously sequester carbon. Material and product circularity contributes to mitigation, such as treatment of organic waste to reduce methane emissions, generate renewable energy, and to substitute for synthetic fertilisers.

The chapter also discusses cross-sectoral mitigation potential related to diffusion of general-purpose technologies (GPT), such as electrification, digitalisation, and hydrogen. Examples include the use of hydrogen as an energy carrier, which, when coupled with low-carbon energy, has potential for driving mitigation in energy, industry, transport, and buildings (Box 12.5), and digitalisation has the potential for reducing GHG emissions through energy savings across multiple sectors.

The efficient realisation of the above examples of cross-sectoral mitigation would require careful design of government interventions across planning, policy, finance, governance, and capacity building fronts. In this respect, Chapter 12 assesses literature on cross-sectoral integrated policies, cross-sectoral financing solutions, cross-sectoral spillovers and competitiveness effects, and on cross-sectoral governance for climate change mitigation.

Finally, in the context of cross-sectoral synergies and trade-offs, the chapter assesses the non-climate mitigation co-benefits and adverse effects in relation to SDGs, building on the fast-growing literature on the non-climate impacts of mitigation.

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=== 12.1.3 Chapter Layout ===

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The chapter is mapped into seven sections. Cost and potentials of mitigation technologies are discussed in [[#12.2|Section 12.2]] , where a comparative assessment and a summary of sectoral mitigation cost and potentials is provided in coordination with the sectoral Chapters 5 to 11, along with a comparison to aggregate cost and potentials based on IAM outputs presented in Chapter 3.

[[#12.3|Section 12.3]] provides a synthesis of the state and potential contribution of CDR methods for addressing climate change. CDR options associated with the agriculture, forestry and other land use (AFOLU) and energy sectors are dealt with in Chapters 6 and 7 and synthesised in [[#12.3|Section 12.3]] . Other methods, not dealt with elsewhere, are covered in more detail. A comparative assessment is provided for the different CDR options in terms of costs, potentials, governance, impacts and risks, and synergies and trade-offs.

[[#12.4|Section 12.4]] assesses the literature on food systems and GHG emissions. The term ‘food system’ refers to a composite of elements (environment, people, inputs, processes, infrastructures, institutions, etc.) and activities that relate to the production, processing, distribution, preparation and consumption of food, and the outputs of these activities, including socio-economic and environmental outcomes. Climate change mitigation opportunities and related implications for sustainable development and adaptation are assessed, including those arising from food production, landscape impacts, supply chain and distribution, and diet shifts.

[[#12.5|Section 12.5]] provides a cross-sectoral perspective on land occupation and related impacts, risks and opportunities associated with land-based mitigation options as well as mitigation options that are not designated land based, yet occupy land. It builds on SRCCL and [[IPCC:Wg3:Chapter:Chapter-7|Chapter 7]] in this report, which covers mitigation in AFOLU, including biomass production for mitigation in other sectors. In addition to an assessment of biophysical and socio-economic risks, impacts and opportunities, this section includes a Cross-Working Group Box (WGII and WGIII) on Mitigation and Adaptation via the Bioeconomy, and a Box on Land Degradation Neutrality as a framework to manage trade-offs in land-based mitigation.

[[#12.6|Section 12.6]] provides a cross-sectoral perspective on mitigation, co-benefits, and trade-offs, including those related to sustainable development and adaptation. The synthesised sectoral mitigation synergies and trade-offs are mapped into options/technologies, policies, international trade, and finance domains. Cross-sectoral mitigation technologies fall into three categories in which the implementation of the technology: (i) occurs in parallel in more than one sector; (ii) could involve interaction between sectors, and/or (iii) could create resource competition among sectors. Policies that have direct sectoral effects include specific policies for reducing GHG emissions and non-climate policies that yield GHG emissions reductions as co-benefits. Policies may also have indirect cross-sectoral effects, including synergies and trade-offs that may, in addition, spill over to other countries.

[[#12.7|Section 12.7]] provides an overview of knowledge gaps, which could be used to inform further research.

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