Editing IPCC:AR6/WGIII/TS (section)

== TS.4 Mitigation and Development Pathways ==

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While previous WGIII assessments have explored mitigation pathways, since AR5 there has been an increasing emphasis in the literature on development pathways, and in particular at the national scale. [https://www.ipcc.ch/chapters/chapter-4 Chapter 4] assesses near-term (2019–2030) to mid-term (2030–2050) pathways, complementing [https://www.ipcc.ch/chapters/chapter-3 Chapter 3] which focuses on long-term pathways (up to 2100). While there is considerable literature on country-level mitigation pathways, including but not limited to NDCs, the country distribution of this literature is very unequal ( ''high confidence'' ). {4.2.1, Cross-Chapter Box 4 in Chapter 4}

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=== TS.4.1 Mitigation and Development Pathways in the Near- to Mid-term ===

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'''An emissions gap persists, exacerbated by an implementation gap, despite mitigation efforts including those in Nationally Determined Contributions (NDCs).''' In this report the ''emissions gap'' is understood as the difference between projected global emissions with Nationally Determined Contributions (NDCs) in 2030, and emissions in 2030 if mitigation pathways consistent with the Paris temperature goals were achieved. The term ''implementation gap'' refers to the gap between NDC mitigation pledges and the expected outcome of existing policies.

'''Pathways consistent with the implementation and extrapolation of countries’ current''' ''[[#footnote-020|13]]'' '''policies see GHG emissions reaching 57 (52–60) GtCO''' ''2'' '''-eq yr''' ''–1'' '''by 2030 and to 46–67 GtC''' '''O''' ''2'' '''-e''' '''q yr''' ''–1'' '''by 2050, leading to a median global warming of 2.4°C to 3.5°C by 2100 (''' '''''medium confidence''''' ''').''' NDCs with unconditional and conditional elements [[#footnote-019|14]] lead to 53 (50–57) and 50 (47–55) GtCO ''2'' -eq, respectively ( ''medium confidence'' ) {Table 4.1} . This leaves median estimated ''emissions gaps'' of 14–23 GtCO ''2'' -eq to limit warming to 2°C and 25–34 GtCO ''2'' -eq to limit warming to 1.5°C relative to mitigation pathways. (Figure TS.9) {Cross-Chapter Box 4, Figure 1 in Chapter 4}

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'''Figure TS.''' '''9 |''' '''Aggregate greenhouse gas (GHG) emissions of global mitigation pathways (coloured funnels and bars) and projected emission outcomes from current policies and emissions implied by unconditional and conditional elements of NDCs, based on updates available by 11 October 2021 (grey bars).''' Shaded areas show GHG emission medians and 25–75th percentiles over 2020–2050 for four types of pathways in the AR6 scenario database: (i) pathways with near-term emissions developments in line with current policies and extended with comparable ambition levels beyond 2030; (ii) pathways ''likely'' to limit warming to 2°C with near-term emissions developments reflecting 2030 emissions implied by current NDCs followed by accelerated emissions reductions; (iii) pathways ''likely'' to limit warming to 2°C based on immediate actions from 2020 onwards; (iv) pathways that limit warming to 1.5°C with no or limited overshoot. Right-hand panels show two snapshots of the 2030 and 2050 emission ranges of the pathways in detail (median, 25–75th and 5–95th percentiles). The 2030 snapshot includes the projected emissions from the implementation of the NDCs as assessed in Section 4.2 (Table 4.1; median and full range). Historic GHG emissions trends as used in model studies are shown for 2010–2015. GHG emissions are in CO 2 -equivalent using GWP100 values from AR6. {3.5, Table 4.1, Cross-Chapter Box 4 in Chapter 4}

'''Projected global emissions from aggregated NDCs place limiting global warming to 1.5°C beyond reach and make it harder after 2030 to limit warming to 2°C (''' '''''high confidence''''' ''').''' Pathways following NDCs until 2030 show a smaller reduction in fossil fuel use, slower deployment of low-carbon alternatives, and a smaller reduction in CO 2 , CH 4 and overall GHG emissions in 2030 compared to immediate action scenarios. This is followed by a much faster reduction of emissions and fossil fuels after 2030, and a larger increase in the deployment of low-carbon alternatives during the medium term in order to get close to the levels of the immediate action pathways in 2050. Those pathways also deploy a larger amount of carbon dioxide removal (CDR) to compensate for higher emissions before 2030. The faster transition during 2030 to 2050 entails greater investment in fossil fuel infrastructure and lower deployment of low-carbon alternatives in 2030, which adds to the socio-economic challenges in realising the higher transition rates. (TS.4.2) {3.5}

'''Studies evaluating up to 105 updated NDCs''' [[#footnote-018|15]] '''indicate that emissions in NDCs with conditional elements have been reduced by 4.5 (2.7–6.3) GtCO''' 2 '''-eq.''' This closes the emission gaps by about one third to 2°C and about 20% to 1.5°C compared to the original NDCs submitted in 2015/16 ( ''medium confidence'' ) {4.2.2, Cross-Chapter Box 4 in Chapter 4} . An ''implementation gap'' also exists between the projected emissions with ‘current policies’ and the projected emissions resulting from the implementation of the unconditional and conditional elements of NDCs; this is estimated to be around 4 and 7 GtCO 2 -eq in 2030, respectively ( ''medium confidence'' ) {4.2.2} . Many countries would therefore require additional policies and associated action on climate change to meet their autonomously determined mitigation targets as specified under the first NDCs ( ''limited evidence'' ). The disruptions triggered by the COVID-19 pandemic increase uncertainty over the range of projections relative to pre-COVID-19 literature. As indicated by a growing number of studies at the national and global level, how large near- to mid-term emissions implications of the COVID-19 pandemic are, to a large degree depends on how stimulus or recovery packages are designed. {4.2}

'''There is a need to explore how accelerated mitigation – relative to NDCs and current policies – could close both emission gaps and implementation gaps.''' There is increasing understanding of the technical content of accelerated mitigation pathways, differentiated by national circumstances, with considerable, though uneven, literature at country-level ( ''medium evidence'' , ''high agreement'' ). Transformative technological and institutional changes for the near term include demand reductions through efficiency and reduced activity, rapid decarbonisation of the electricity sector and low-carbon electrification of buildings, industry and transport ( ''robust evidence'' , ''medium agreement'' ). A focus on energy use and supply is essential, but not sufficient on its own – the land sector and food systems deserve attention. The literature does not adequately include demand-side options and systems analysis, and captures the impact from non-CO 2 GHGs ( ''medium confidence'' ). {4.2.5}

'''If obstacles to accelerated mitigation are rooted in underlying structural features of society, then transforming such structures can support emission reductions {4.2.6} .''' Countries and regions will have different starting points for transition pathways. Some critical differences between countries include climate conditions resulting in different heating and cooling needs, endowments with different energy resources, patterns of spatial development, and political and economic conditions {4.2.5} . The way countries develop determines their capacity to accelerate mitigation and achieve other sustainable development objectives simultaneously ( ''medium confidence'' ) {4.3.1, 4.3.2} . Yet meeting ambitious mitigation and development goals cannot be achieved through incremental change ( ''robust evidence'' , ''medium agreement'' ). Though development pathways result from the actions of a wide range of actors, it is possible to shift development pathways through policies and enhancing enabling conditions ( ''limited evidence'' , ''medium agreement'' ).

'''''Shifting development pathways towards sustainability''''' '''offers ways to broaden the range of levers and enablers that a society can use to accelerate mitigation and increases the likelihood of making progress simultaneously on climate action and other development goals (Box TS.3) {Cross-Chapter Box 5 in Chapter 4, Figure 4.7, 4.3} .''' There are practical options to shift development pathways in ways that advance mitigation and other sustainable development objectives, support political feasibility, increase resources to meet multiple goals, and reduce emissions ( ''limited evidence'' , ''high agreement'' ). Concrete examples, assessed in [https://www.ipcc.ch/chapters/chapter-4 Chapter 4] of this report, include high-employment and low-emissions structural change; fiscal reforms for mitigation and social contract, combining housing policies to deliver both housing and transport mitigation; and changed economic, social and spatial patterns of agriculture sector development, providing the basis for sustained reductions in emissions from deforestation. {4.4.1, 4.4, 1.10}

'''Table TS.''' '''2 |''' '''Comparison of key characteristics of mitigation pathways with immediate action towards limiting warming to 1.5-2°C vs. pathways following NDCs announced prior to COP26 until 2030.''' Key characteristics are reported for five groups of mitigation pathways: (i) immediate action to limit warming to 1.5°C (&gt;50%) with no or limited overshoot (C1 in Table TS.3; 97 scenarios), (ii) near term action following the NDCs until 2030 and returning warming to 1.5°C (&gt; 50%) by 2100 after a high overshoot (subset of 42 scenarios following the NDCs until 2030 in C2), (iii) immediate action to limit warming to 2°C (&gt;67%), (C3a in Table TS.3; 204 scenarios), (iv) near term action following the NDCs until 2030 followed by post-2030 action to limit warming to 2°C (&gt;67%) (C3b in Table TS.3; 97 scenarios). Also shown are the characteristics for (v) the combined class of all scenarios that limit warming to 2°C (&gt;67%). The groups (i), (iii), and the combination of (ii) and (iv) are depicted in Figure TS.9. Reported are median and interquartile ranges (in brackets) for selected global indicators. Numbers are rounded to the nearest five, with the exception of cumulative net negative CO 2 emissions rounded to the nearest 10. Changes from 2019 are relative to modelled 2019 values. Emissions reductions are based on harmonised model emissions used for the climate assessment. {Section 3.5} {Table 3.6}

{| class="wikitable"
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| rowspan="2"| Global indicators

| '''1.5°C (&gt;50%)'''

| 1.5°C (&gt;50%) by 2100

| colspan="3"| 2°C (&gt;67%)

|-
| Immediate action, with no or limited overshoot

| NDCs until 2030, with overshoot before 2100

| ''Immediate action''

| NDCs until 2030

| All

|-
| Cumulative net negative CO 2 emissions

until 2100 (GtCO 2 )

| 220 (70,430)

| 380 (300,470)

| 30 (0,130)

| 60 (20,210)

| 40 (10,180)

|-
| Change in GHG emissions in 2030 (% rel to 2019)

| –45 (–50,–40)

| –5 (–5,0)

| –25 (–35,–20)

| –5 (–10,0)

| –20 (–30,–10)

|-
| in 2050 (% rel to 2019)

| –85 (–90,–80)

| –75 (–85,–70)

| –65 (–70,–60)

| –70 (–70,–60)

| –65 (–70,–60)

|-
| Change in CO 2 emissions in 2030 (% rel to 2019)

| –50 (–60,–40)

| –5 (–5,0)

| –25 (–35,–20)

| –5 (–5,0)

| –20 (–30,–5)

|-
| in 2050 (% rel to 2019)

| –100 (–105,–95)

| –85 (–95,–80)

| –70 (–80,–65)

| –75 (–80,–65)

| –75 (–80,–65)

|-
| Change in net land use CO 2 emissions in 2030 (% rel to 2019)

| –100 (–105,–95)

| –30 (–60,–20)

| –90 (–105,–75)

| –20 (–80,–20)

| –80 (–100,–30)

|-
| in 2050 (% rel to 2019)

| –150 (–200,–100)

| –135 (–165,–120)

| –135 (–185,–100)

| –130 (–145,–115)

| –135 (–180,–100)

|-
| Change in CH 4 emissions in 2030 (% rel to 2019)

| –35 (–40,–30)

| –5 (–5,0)

| –25 (–35,–20)

| –10 (–15,–5)

| –20 (–25,–10)

|-
| in 2050 (% rel to 2019)

| –50 (–60,–45)

| –50 (–60,–45)

| –45 (–50,–40)

| –50 (–65,–45)

| –45 (–55,–40)

|-
| Change in primary energy from coal in 2030 (% rel to 2019)

| –75 (–80,–65)

| –10 (–20,–5)

| –50 (–65,–35)

| –15 (–20,–10)

| –35 (–55,–20)

|-
| in 2050 (% rel to 2019)

| –95 (–100,–80)

| –90 (–100,–85)

| –85 (–100,–65)

| –80 (–90,–70)

| –85 (–95,–65)

|-
| Change in primary energy from oil in 2030 (% rel to 2019)

| –10 (–25,0)

| 5 (5,10)

| 0 (–10,10)

| 10 (5,10)

| 5 (0,10)

|-
| in 2050 (% rel to 2019)

| –60 (–75,–40)

| –50 (–65,–35)

| –30 (–45,–15)

| –40 (–55,–20)

| –30 (–50,–15)

|-
| Change in primary energy from gas in 2030 (% rel to 2019)

| –10 (–30,0)

| 15 (10,25)

| 10 (0,15)

| 15 (10,15)

| 10 (0,15)

|-
| in 2050 (% rel to 2019)

| –45 (–60,–20)

| –45 (–55,–30)

| –10 (–35,15)

| –30 (–45,–5)

| –15 (–40,10)

|-
| Change in primary energy from nuclear in 2030 (% rel to 2019)

| 40 (10,70)

| 10 (0,25)

| 35 (5,50)

| 10 (0,30)

| 25 (0,45)

|-
| in 2050 (% rel to 2019)

| 90 (15,295)

| 100 (45,130)

| 85 (30,200)

| 75 (30,120)

| 80 (30,140)

|-
| Change in primary energy from modern biomass in 2030 (% rel to 2019)

| 75 (55,130)

| 45 (20,75)

| 60 (35,105)

| 45 (20,80)

| 55 (35,105)

|-
| in 2050 (% rel to 2019)

| 290 (215,430)

| 230 (170,420)

| 240 (130,355)

| 260 (95,435)

| 250 (115,405)

|-
| Change in primary energy from non-biomass renewables in 2030 (% rel to 2019)

| 225 (155,270)

| 100 (85,145)

| 150 (115,190)

| 115 (85,130)

| 130 (90,170)

|-
| in 2050 (% rel to 2019)

| 725 (545,950)

| 665 (535,925)

| 565 (415,765)

| 625 (545,700)

| 605 (470,735)

|-
| Change in carbon intensity of electricity in 2030 (% rel to 2019)

| –75 (–80,–70)

| –30 (–40,–30)

| –60 (–70,–50)

| –35 (–40,–30)

| –50 (–65,–35)

|-
| in 2050 (% rel to 2019)

| –100 (–100,–100)

| –100 (–100,–100)

| –95 (–100,–95)

| –100 (–100,–95)

| –95 (–100,–95)

|}

'''Box TS.3 |''' '''Shifting Development Pathways to Increase Sustainability and Broaden Mitigation Options'''

In this report, ''development pathways'' refer to the patterns of development resulting from multiple decisions and choices made by many actors in the national and global contexts. Each society whether in developing or developed regions follows its own pattern of growth (Figure TS.13). Development pathways can also be described at smaller scales (e.g., for regions or cities) and for sectoral systems.

Development pathways are major drivers of GHG emissions {1, 2} . There is compelling evidence to show that continuing along existing development pathways will not achieve rapid and deep emission reductions. In the absence of shifts in development pathways, conventional mitigation policy instruments may not be able to limit global emissions to a degree sufficient to meet ambitious mitigation goals or they may only be able to do so at very high economic and social costs.

Policies to shift development pathways, on the other hand, make mitigation policies more effective. Shifting development pathways broadens the scope for synergies between sustainable development objectives and mitigation. Development pathways also determine the enablers and levers available for adaptation {AR6 WGII TS.E.1.2} and for achieving other SDGs.

There are many instances in which reducing GHG emissions and moving towards the achievement of other development objectives can go hand in hand {Chapter 3, Figure 3.33, Chapters 6–12, and 17} . Integrated policies can support the creation of synergies between ''action to combat climate change and its impacts'' (SDG 13 – climate action) and other SDGs. For example, when measures promoting walkable urban areas are combined with electrification and clean renewable energy, there are several co-benefits to be attained. These include reduced pressures on agricultural land from reduced urban growth, health co-benefits from cleaner air, and benefits from enhanced mobility {8.2, 8.4, 4.4.1} . Energy efficiency in buildings and energy poverty alleviation through improved access to clean fuels also deliver significant health benefits. {9.8.1 and 9.8.2}

However, decisions about mitigation actions, and their timing and scale, may entail trade-offs with the achievement of other national development objectives in the near, mid- and long term {Chapter 12} . In the near term, for example, regulations may ban vehicles from city centres to reduce congestion and local air pollution but reduce mobility and choice. Increasing green spaces within cities without caps on housing prices may involve trade-offs with affordable housing and push low-income residents outside the city {8.2.2} . In the mid- and long term, large-scale deployment of biomass energy raises concerns about food security and biodiversity conservation {3.7.1, 3.7.5, 7.4.4, 9.8.1, 12.5.2, 12.5.3} . Prioritising is one way to manage these trade-offs, addressing some national development objectives earlier than others. Another way is to adopt policy packages aimed at shifting development pathways towards increased sustainability (SDPS) as they expand the range of tools available to simultaneously achieve multiple development objectives and accelerate mitigation. (Box TS.3, Figure 1)

'''What does shifting development pathways towards increased sustainability entail?'''

Shifting development pathways towards increased sustainability implies making transformative changes that disrupt existing developmental trends. Such choices would not be marginal, but include technological, systemic and socio-behavioural changes {4.4} . Decision points also arise with new infrastructure, sustainable supply chains, institutional capacities for evidence-based and integrated decision-making, financial alignment towards low-carbon socially responsible investments, just transitions and shifts in behaviour and norms to support shifts away from fossil fuel consumption. Adopting multi-level governance modes, tackling corruption where it inhibits shifts to sustainability, and improving social and political trust are also key for aligning and supporting long-term environmentally just policies and processes. {4.4, Cross-Chapter Box 5 in Chapter 4}

'''How can development pathways be ‘shifted’?'''

Shifting development paths is complex. Changes that involve ‘dissimilar, unfamiliar and more complex science-based components’ take more time, acceptance and legitimation and involve complex social learning, even when they promise large gains. Despite the complexities of the interactions that result in patterns of development, history also shows that societies can influence the direction of development pathways based on choices made by decision-makers, citizens, the private sector, and social stakeholders. Shifts in development pathways result from both sustained political interventions and bottom-up changes in public opinion. Collective action by individuals as part of social movements or lifestyle changes underpins system change. {5.2.3, 5.4.1, 5.4.5}

Sectoral transitions that aim to shift development pathways often have multiple objectives and deploy a diverse mix of policies and institutional measures. Context-specific governance conditions can significantly enable or disable sectoral transitions. {Cross-Chapter Box 12 in Chapter 16}

The necessary transformational changes are anticipated to be more acceptable if rooted in the development aspirations of the economy and society within which they take place and may enable a new social contract to address a complex set of interlinkages across sectors, classes, and the whole economy. Taking advantage of windows of opportunity and disruptions to mindsets and socio-technical systems could advance deeper transformations.

'''How can shifts in development pathways be implemented by actors in different contexts?'''

Shifting development pathways to increased sustainability is a shared aspiration. Yet since countries differ in starting points (e.g., social, economic, cultural, political) and historical backgrounds, they have different urgent needs in terms of facilitating the economic, social, and environmental dimensions of sustainable development and, therefore, give different priorities {4.3.2, 17.1} . The appropriate set of policies to shift development pathways thus depends on national circumstances and capacities.

Shifting development pathways towards sustainability needs to be supported by multilateral partnerships to strengthen suitable capacity, technological innovation (TS.6.5), and financial flows (TS.6.4). The international community can play a particularly key role by helping ensure the necessary broad participation in climate-mitigation efforts, including by countries at different development levels, through sustained support for policies and partnerships that support shifting development pathways towards sustainability while promoting equity and being mindful of different transition capacities. {4.3, 16.5, 16.6}

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'''Box TS.3, Figure 1 |''' '''Shifting development pathways to increased sustainability: choices by a wide range of actors at key decision points on development pathways can reduce barriers and provide more tools to accelerate mitigation and achieve other Sustainable Development Goals.''' {4.7}

'''Policies can''' '''''shift''''' '''development pathways. There are examples of policies implemented in the pursuit of overall societal development objectives, such as job creation, macroeconomic stability, economic growth, and public health and welfare.''' In some countries, such policies are framed as part of a ''Just Transition'' (Box TS.3), however, they can have major influence on mitigative capacity, and hence can be seen as tools to broaden mitigation options ( ''medium confidence'' ) {4.3.3} . Coordinated policy mixes would need to orchestrate multiple actors – individuals, groups and collectives, corporate actors, institutions and infrastructure actors – to deepen decarbonisation and shift pathways towards sustainability. Shifts in one country may spill over to other countries. Shifting development pathways can jointly support mitigation and adaptation {4.4.2} . Some studies explore the risks of high complexity and potential delay attached to shifting development pathways. (Box TS.4, Figure TS.11) {4.4.3}

'''An increasing number of mitigation strategies up to 2050 (mid-term) have been developed by various actors. A growing number of such strategies aim at net zero GHG or CO''' 2 '''emissions, but it is not yet possible to draw global implications due to the limited size of sample (''' '''''medium evidence, low agreement''''' ''') {4.2.4} .''' Non-state actors are also engaging in a wide range of mitigation initiatives. When adding up emission reduction potentials, sub-national and non-state international cooperative initiatives could reduce emissions by up to about 20 GtCO 2 -eq in 2030 ( ''limited evidence'' , ''medium agreement'' ) {4.2.3} . Yet perceived or real conflicts between mitigation and other SDGs can impede such action. If undertaken without precaution, accelerated mitigation is found to have significant implications for development objectives and macroeconomic costs at country level. The literature shows that the employment effect of mitigation policies tends to be limited on aggregate but can be significant at sectoral level ( ''limited evidence'' , ''medium agreement'' ). Detailed design of mitigation policies is critical for distributional impacts and avoiding lock-in ( ''high confidence'' ), though further research is needed in that direction. {4.2.6}

'''The literature identifies a broad set of enabling conditions that can both foster''' '''''shifting development pathways''''' '''and''' '''''accelerated mitigation''''' '''(''' '''''medium evidence, high agreement''''' ''').''' Policy integration is a necessary component of shifting development pathways, addressing multiple objectives. To this aim, mobilising a range of policies is preferable to single policy instruments ( ''high confidence'' ). {4.4.1} . Governance for climate mitigation and shifting development pathways is enhanced when tailored to national and local contexts. Improved institutions and effective governance enable ambitious action on climate and can help bridge implementation gaps ( ''medium evidence'' , ''high agreement'' ). Given that strengthening institutions may be a long-term endeavour, it needs attention in the near term {4.4.1} . Accelerated mitigation and shifting development pathways necessitates both redirecting existing financial flows from high- to low-emissions technologies and systems, and providing additional resources to overcome current financial barriers ( ''high confidence'' ) {4.4.1} . Opportunities exist in the near term to close the finance gap {15.2.2} . At the national level, public finance for actions promoting sustainable development helps broaden the scope of mitigation ( ''medium confidence'' ). Changes in behaviour and lifestyles are important to move beyond mitigation as incremental change, and when supporting shifts to more sustainable development pathways will broaden the scope of mitigation ( ''medium confidence'' ). {4.4.1, Figure 4.8}

'''Some enabling conditions can be put in place relatively quickly while some others may take time to establish underscoring the importance of early action (''' '''''high confidence''''' ''').''' Depending on context, some enabling conditions such as promoting innovation may take time to establish. Other enabling conditions, such as improved access to financing, can be put in place in a relatively short time frame, and can yield rapid results {4.4, Figure 5.14, 13.9, 14.5, 15.6, 16.3, 16.4, 16.5, Cross-Chapter Box 12 in Chapter 16} . Focusing on development pathways and considering how to shift them may also yield rapid results by providing tools to accelerate mitigation and achieve other sustainable development goals {4.4.1} . Charting just transitions to net zero may provide a vision, which policy measures can help achieve (Boxes TS.4 and TS.8).

'''Equity can be an important enabler, increasing the level of ambition for accelerated mitigation (''' '''''high confidence''''' ''') {4.5} .''' Equity deals with the distribution of costs and benefits and how these are shared, as per social contracts, national policy and international agreements. Transition pathways have distributional consequences such as large changes in employment and economic structure ( ''high confidence'' ). The ''Just Transition'' concept has become an international focal point tying together social movements, trade unions, and other key stakeholders to ensure equity is better accounted for in low-carbon transitions (Box TS.4). The effectiveness of cooperative action and the perception of fairness of such arrangements are closely related in that pathways that prioritise equity and allow broad stakeholder participation can enable broader consensus for the transformational change implicit in the need for deeper mitigation ( ''robust evidence'' , ''medium agreement'' ). (Box TS.4) {4.5, Figure 4.9}

'''Box TS.4 | Just Transition'''

The Just Transition framework refers to a set of principles, processes and practices aimed at ensuring that no people, workers, places, sectors, countries or regions are left behind in the move from a high-carbon to a low-carbon economy. It includes respect and dignity for vulnerable groups; creation of decent jobs; social protection; employment rights; fairness in energy access and use and social dialogue and democratic consultation with relevant stakeholders.

The concept has evolved, becoming prominent in the United States of America in 1980, related to environmental regulations that resulted in job losses from highly polluting industries. Traced from a purely labour movement, trade union space, the Just Transition framework emphasises that decent work and environmental protection are not incompatible. During COP 24, with the Just Transition Silesia Declaration, the concept gained in recognition and was signed by 56 heads of state.

Implicit in a Just Transition is the notion of well-being, equity and justice – the realisation that transitions are inherently disruptive and deliberate effort may be required to ensure communities dependent on fossil-fuel based economies and industries do not suffer disproportionately {Chapter 4} . ‘Just Transitions’ are integral to the European Union as mentioned in the EU Green Deal, the Scottish Government’s development plans and other national low-carbon transition strategies. The US Green New Deal Resolution puts structural inequality, poverty mitigation, and ‘Just Transitions’ at its centre. There is a growing awareness of the need for shifting finance towards Just Transition in the context of COVID-19, in particular, public finance and governance have a major role in allowing a Just Transition more broadly {Chapter 15} .

In the immediate aftermath of the COVID-19 pandemic, low oil prices created additional financial problems for fossil fuel producer countries faced with loss of revenue and reduced fiscal latitude and space. Public spending and social safety nets associated with the proceeds from producer economies can be affected as assets become stranded and spending on strategic sustainable development goals such as free education and health-care services are neglected. Fiscal challenges are intricately linked to ‘Just Transitions’ and the management associated with sustainable energy transition. There is no certainty on how energy systems will recover post-COVID-19. However, ‘Just Transitions’ will have equity implications if stimulus packages are implemented without due regard for the differentiated scales and speeds and national and regional contexts, especially in the context of developing countries.

A Just Transition entails targeted and proactive measures from governments, agencies, and other non-state authorities to ensure that any negative social, environmental, or economic impacts of economy-wide transitions are minimised, whilst benefits are maximised for those disproportionally affected. These proactive measures include eradication of poverty, regulating prosperity and creating jobs in ‘green’ sectors. In addition, governments, polluting industries, corporations, and those more able to pay higher associated taxes, can pay for transition costs by providing a welfare safety net and adequate compensation to people, communities, and regions that have been impacted by pollution, or are marginalised, or are negatively impacted by a transition from a high- to low-carbon economy and society. There is, nonetheless, increased recognition that resources that can enable the transition, international development institutions, as well as other transitional drivers such as tools, strategies and finance, are scarce. A sample of global efforts is summarised in Box TS.4, Figure 1.

[[File:b7c6d02de94ae24737c33ceb48344863 IPCC_AR6_WGIII_Box_TS_4_Figure_1.png]]

'''Box TS.4 Figure 1 |''' '''Just Transitions around the world, 2020. Panel (a)''' shows commissions, task forces, and dialogues behind a Just Transition in many countries. '''Panel (b)''' shows the funds related to the Just Transition within the European Union Green Deal. '''Panel (c)''' shows the European Union’s Platform for Coal Regions in Transition. {Figure 4.9}

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=== TS.4.2 Long-term Mitigation Pathways ===

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'''The characteristics of a wide range of long-term mitigation pathways, their common elements and differences are assessed in Chapter 3. Differences between pathways typically represent choices that can steer the system in alternative directions through the selection of different combinations of response options''' '''(''' '''''high confidence''''' ''').''' More than 2000 quantitative emissions pathways were submitted to the AR6 scenarios database, of which more than 1200 pathways included sufficient information for the associated warming to be assessed (consistent with AR6 WGI methods). (Box TS.5) {3.2, 3.3}

'''Many pathways in the literature show how to limit global warming to 2°C (&gt;67%) with no overshoot or to limit warming to 1.5°C (&gt;50%) with limited overshoot compared to''' '''1850–1900''' '''. The likelihood of limiting warming to 1.5°C with no or limited overshoot has dropped in AR6 WGIII compared to AR6 SR1.5 because global GHG emissions have risen since 2017, leading to higher near-term emissions (2030) and higher cumulative CO''' 2 '''emissions until the time of net zero (''' '''''medium confidence''''' ''').''' Only a small number of published pathways limit global warming to 1.5°C without overshoot over the course of the 21st century. {3.3, Annex III.II.3}

'''Mitigation pathways limiting warming to 1.5°C with no or limited overshoot reach 50% CO''' 2 '''reductions in the 2030s, relative to 2019, then reduce emissions further to reach net zero CO''' 2 '''emissions in the 2050s. Pathways limiting warming to 2°C (&gt;67%) reach 50% reductions in the 2040s and net zero CO''' 2 '''by the 2070s (''' '''''medium confidence''''' ''').''' (Figure TS.10, Box TS.6) {3.3}

'''Cost-effective mitigation pathways assuming immediate action to limit warming to 2°C (&gt;67%) are associated with net global GHG emissions of 30–49 GtCO''' 2 '''-eq yr''' –1 '''by 2030 and 14–27 GtCO''' 2 '''-eq yr''' –1 '''by 2050 (''' '''''medium confidence''''' ''').''' This corresponds to reductions, relative to 2019 levels, of 13–45% by 2030 and 52–76% by 2050. Pathways that limit global warming to below 1.5°C with no or limited overshoot require a further acceleration in the pace of transformation, with net GHG emissions typically around 21–36 GtCO 2 -eq yr –1 by 2030 and 1–15 GtCO 2 -eq yr –1 by 2050; this corresponds to reductions of 34–60% by 2030 and 73–98% by 2050 relative to 2019 levels. {3.3}

'''Box TS.5 | Illustrative Mitigation Pathways (IMPs), and Shared Socio-economic Pathways (SSPs)'''

'''The Illustrative Mitigation Pathways (IMPs)'''
The over 2500 model-based pathways submitted to the AR6 scenarios database pathways explore different possible evolutions of future energy and land use (with and without climate policy) and the consequences for greenhouse gas emissions.

From the full range of pathways, five archetype scenarios – referred to in this report as ''Illustrative Mitigation Pathways'' (IMPs) – were selected to illustrate key mitigation-strategy themes that flow through several chapters in this report. A further two ''pathways illustrative of high emissions'' assuming continuation of current policies or moderately increased action were selected to show the consequences of current policies and pledges. Together these pathways provide illustrations of potential future developments that can be shaped by human choices, including: Where are current policies and pledges leading us? What is needed to reach specific temperature goals? What are the consequences of using different strategies to meet these goals? What are the consequences of delay? How can we shift development from current practices to give higher priority to sustainability and the SDGs?

Each of the IMPs comprises: a ''storyline'' and a ''quantitative illustration'' . The ''storyline'' describes the key characteristics of the pathway qualitatively; the ''quantitative illustration'' is selected from the literature on long-term scenarios to effectively represent the IMP numerically. The five Illustrative Mitigation Pathways (IMPs) each emphasise a different scenario element as its defining feature, and are named accordingly: heavy reliance on ren ewables (IMP-Ren), strong emphasis on l ow d emand for energy (IMP-LD), extensive use of carbon dioxide removal (CDR) in the energy and the industry sectors to achieve net negative emissions (IMP-Neg), mitigation in the context of broader sustainable development and s hifting development p athways (IMP-SP), and the implications of a less rapid and g radual s trengthening of near-term mitigation actions (IMP-GS). In some cases, sectoral chapters may use different quantifications that follow the same storyline narrative but contain data that better exemplify the chapter’s assessment. Some IMP variants are also used to explore the sensitivity around alternative temperature goals. {3.2, 3.3}

The two additional ''pathways illustrative of higher emissions'' are current policies (CurPol) and moderate action (ModAct).

This framework is summarised in Box TS.5, Table.1 below, which also shows where the IMPs are situated with respect to the classification of emissions scenarios into warming levels (C1–C8) introduced in Chapter 3, and the CMIP6 (Coupled Model Intercomparison Project 6) scenarios used in the AR6 WGI report.

'''Box TS.5, Table.1 |''' '''Illustrative Mitigation Pathways (IMPs) and pathways illustrative of higher emissions in relation to scenarios’ categories, and CMIP6 scenarios.'''

{| class="wikitable"
|-
| '''Classification of emissions scenarios into warming levels: C1–C8'''

| '''Pathways illustrative of higher emissions'''

| '''Illustrative mitigation pathways (IMPs)'''

| '''CMIP6 scenarios'''

|-
| '''C8''' exceeding warming of 4°C (≥50%)

|
| SSP5-8.5

|-
| '''C7''' limit warming to 4°C (&gt;50%)

| CurPol

|
| SSP3-7.0

|-
| '''C6''' limit warming to 3°C (&gt;50%)

| ModAct

|
| SSP2-4.5

|-
| '''C5''' limit warming to 2.5°C (&gt;50%)

|
| SSP4-3.7

|-
| '''C4''' limit warming to 2°C (&gt;50%)

|
|-
| '''C3''' limit warming to 2°C (&gt;67%)

|
| IMP-GS

(Sensitivities: Neg; Ren)

| SSP2-2.6

|-
| '''C2''' return warming to 1.5°C (&gt;50%) after a high overshoot

|
| IMP-Neg

|
|-
| '''C1''' limit warming to 1.5°C (&gt;50%) with no or limited overshoot

|
| IMP-LD

IMP-Ren

IMP-SP

| SSP1-1.9

|}

'''The Shared Socio-economic Pathways (SSPs)'''
First published in 2017, the Shared Socio-economic Pathways (SSPs) are alternative projections of socio-economic developments that may influence future GHG emissions.

The initial set of SSP narratives described worlds with different challenges to mitigation and adaptation: SSP1 ( ''sustainability'' ), SSP2 ( ''middle of the road'' ), SSP3 ( ''regional rivalry'' ), SSP4 ( ''inequality'' ) and SSP5 ( ''rapid growth'' ). The SSPs were subsequently quantified in terms of energy, land-use change, and emission pathways for both (i) no-climate-policy reference scenarios and (ii) mitigation scenarios that follow similar radiative forcing pathways as the representative concentration pathways (RCPs) assessed in AR5 WGI. {3.2.3}

Most of the scenarios in the AR6 database are SSP-based. The majority of the assessed scenarios are consistent with SSP2. Using the SSPs permits a more systematic assessment of future GHG emissions and their uncertainties than was possible in AR5. The main emissions drivers across the SSPs include growth in population reaching 8.5–9.7 billion by 2050, and an increase in global GDP of 2.7–4.1% per year between 2015 and 2050. Final energy demand in the absence of any new climate policies is projected to grow to around 480 to 750 EJ yr –1 in 2050 (compared to around 390 EJ yr –1 in 2015) ( ''medium confidence'' ) ''.'' The highest emissions scenarios in the literature result in global warming of &gt;5 '''°''' C by 2100, based on assumptions of rapid economic growth and pervasive climate policy failures ( ''high confidence'' ). {3.3}

'''Pathways following current NDCs until 2030 reach annual emissions of 47–57 GtCO''' ''2'' '''-eq yr''' ''–1'' '''by 2030, thereby making it impossible to limit warming to 1.5°C (&gt;50%) with no or limited overshoot and strongly increasing the challenge of limiting warming to 2°C (&gt;67%) (''' '''''high confidence''''' ''').''' A high overshoot of 1.5°C increases the risks from climate impacts and increases dependence on large-scale carbon dioxide removal (CDR) from the atmosphere. A future consistent with current NDCs implies higher fossil fuel deployment and lower reliance on low-carbon alternatives until 2030, compared to mitigation pathways describing immediate action that limits warming to 1.5°C (&gt;50%) with no or limited overshoot, or limits warming to 2°C (&gt;67%) and below. After following the NDCs to 2030, to limit warming to 2°C (&gt;67%) the pace of global GHG emission reductions would need to abruptly increase from 2030 onward to an average of 1.3–2.1 GtCO ''2'' -eq per year between 2030 and 2050. This is similar to the global CO ''2'' emission reductions in 2020 that occurred due to the COVID-19 pandemic lockdowns, and around 70% faster than in pathways where immediate action is taken to limit warming to 2°C (&gt;67%). Accelerating emission reductions after following an NDC pathway to 2030 would also be particularly challenging because of the continued buildup of fossil fuel infrastructure that would take place between now and 2030. (TS4.1, Table TS.3) {3.5, 4.2}

'''Table TS''' '''.3 |''' '''GHG, CO''' 2 '''emissions and warming characteristics of different mitigation pathways submitted to the AR6 scenarios database, and as categorised in the climate assessment. {Table 3.2}'''

{| class="wikitable"
|-
! colspan="3"| '''p50 [p5–p95]''' a

! colspan="3"| '''GHG emissions (''' '''GtCO''' 2 '''-eq''' '''y''' '''r''' –1 ''')''' g

! colspan="3"| '''GHG emissions reductions from 2019 (%)''' h

! colspan="4"| '''Emissions milestones''' i, j

! colspan="2"| '''Cumulative CO''' 2 '''emissions (GtCO''' 2 ''')''' m

! '''Cumulative''' '''net-negative''' '''CO''' 2 '''emissions (GtCO''' 2 ''')'''

! colspan="2"| '''Global mean temperature changes 50% probability''' '''(''' °C ''')''' n

! colspan="3"| '''Likelihood of peak global warming staying below (%)''' o

|-
! '''Categor''' '''y''' b, c, d '''[# pathways]'''

! '''Category/subset label'''

! '''WGI SSP &amp; WGIII IPs/IMPs''' '''alignmen''' '''t''' e, f

! '''2030'''

! '''2040'''

! '''2050'''

! '''2030'''

! '''2040'''

! '''2050'''

! '''Peak CO''' 2 '''emissions (% peak before 2100)'''

! '''Peak GHG emissions (% peak before 2100)'''

! '''Net zero''' '''CO''' 2 '''(%''' '''net zero''' '''pathways)'''

! '''Net zero''' '''GHGs (%''' '''net zero''' '''pathways)''' k, l

! '''2020 to''' '''net zero''' '''CO''' 2

! '''2020–2100'''

! '''Year of''' '''net zero''' '''CO''' 2 '''to 2100'''

! '''at peak warming'''

! '''2100'''

! '''&lt;1.5°C'''

! '''&lt;2.0°C'''

! '''&lt;3.0°C'''

|-
! colspan="3"| Modelled global emissions pathways categorised by projected global warming levels (GWL). Detailed likelihood definitions are provided in SPM Box 1.

The five illustrative scenarios ( SSPx-yy ) considered by AR6 WGI and the Illustrative (Mitigation) Pathways assessed in WGIII are aligned with the temperature categories and are indicated in a separate column. Global emission pathways contain regionally differentiated information. This assessment focuses on their global characteristics.

! colspan="3"| Projected median annual GHG emissions in the year across the scenarios, with the 5th–95th percentile in brackets.

Modelled GHG emissions in 2019: 55 [53–58] GtCO 2 -eq .

! colspan="3"| Projected median GHG emissions reductions of pathways in the year across the scenarios compared to modelled 2019, with the 5th–95th percentile in brackets. Negative numbers indicate increase in emissions compared to 2019.

! colspan="2"| Median 5-year intervals at which projected CO 2 &amp; GHG emissions peak, with the 5th–95th percentile interval in square brackets. Percentage of peaking pathways is denoted in round brackets.

Three dots (…) denotes emissions peak in 2100 or beyond for that percentile.

! colspan="2"| Median 5-year intervals at which projected CO 2 &amp; GHG emissions of pathways in this category reach net zero , with the 5th–95th percentile interval in square brackets. Percentage of net zero pathways is denoted in round brackets.

Three dots (…) denotes net zero not reached for that percentile.

! colspan="2"| Median cumulative net CO 2 emissions across the projected scenarios in this category until reaching net zero or until 2100, with the 5th–95th percentile interval in square brackets.

! Median cumulative net-negative CO 2 emissions between the year of net zero CO 2 and 2100. More net-negative results in greater temperature declines after peak.

! colspan="2"| Projected temperature change of pathways in this category (50% probability across the range of climate uncertainties), relative to 1850–1900, at peak warming and in 2100, for the median value across the scenarios and the 5th–95th percentile interval in square brackets.

! colspan="3"| Median likelihood that the projected pathways in this category stay below a given global warming level, with the 5th–95th percentile interval in square brackets.

|-
| '''C1 [97]'''

| '''limit warming to 1.5°C (&gt;50%) with no or limited overshoot'''

|
| 31

[21–36]

| 17

[6–23]

| 9

[1–15]

| 43

[34–60]

| 69

[58–90]

| 84

[73–98]

| rowspan="4" colspan="2"| 2020–2025 (100%)

[2020–2025]

| rowspan="4"| 2050–2055 (100%)

[2035–2070]

| 2095–2100 (52%)

[2050–...]

| 510

[330–710]

| 320

[–210 to 570]

| –220

[–660 to –20]

| 1.6

[1.4–1.6]

| 1.3

[1.1–1.5]

| 38

[33–58]

| 90

[86–97]

| 100

[99–100]

|-
| '''C1a [50]'''

| '''… with''' '''net zero''' '''GHGs'''

| SSP1–1.9,

SP

LD

| 33

[22–37]

| 18

[6–24]

| 8

[0–15]

| 41

[31–59]

| 66

[58–89]

| 85

[72–100]

| 2070–2075 (100%)

[2050–2090]

| 550

[340–760]

| 160

[–220 to 620]

| –360

[–680 to –140]

| 1.6

[1.4–1.6]

| 1.2

[1.1–1.4]

| 38

[34–60]

| 90

[85–98]

| 100

[99–100]

|-
| rowspan="2"| '''C1b [47]'''

| rowspan="2"| '''… without''' '''net zero''' '''GHGs'''

| rowspan="2"| Ren

| rowspan="2"| 29

[21–36]

| rowspan="2"| 16

[7–21]

| rowspan="2"| 9

[4–13]

| rowspan="2"| 48

[35–61]

| rowspan="2"| 70

[62–87]

| rowspan="2"| 84

[76–93]

| …–… [0%]

| rowspan="2"| 460

[320–590]

| rowspan="2"| 360

[10–540]

| rowspan="2"| –60

[–440 to 0]

| rowspan="2"| 1.6

[1.5–1.6]

| rowspan="2"| 1.4

[1.3–1.5]

| rowspan="2"| 37

[33–56]

| rowspan="2"| 89

[87–96]

| rowspan="2"| 100

[99–100]

|-
| […–…]

|-
| rowspan="2"| '''C2 [133]'''

| rowspan="2"| '''return warming to 1.5°C (&gt;50%) after a high overshoot'''

| rowspan="2"| Neg

| rowspan="2"| 42

[31–55]

| rowspan="2"| 25

[17–34]

| rowspan="2"| 14

[5–21]

| rowspan="2"| 23

[0–44]

| rowspan="2"| 55

[40–71]

| rowspan="2"| 75

[62–91]

| colspan="2"| 2020–2025 (100%)

| rowspan="2"| 2055–2060 (100%)

[2045–2070]

| rowspan="2"| 2070–2075 (87%)

[2055–...]

| rowspan="2"| 720

[530–930]

| rowspan="2"| 400

[–90 to 620]

| rowspan="2"| –360

[–680 to –60]

| rowspan="2"| 1.7

[1.5–1.8]

| rowspan="2"| 1.4

[1.2–1.5]

| rowspan="2"| 24

[15–42]

| rowspan="2"| 82

[71–93]

| rowspan="2"| 100

[99–100]

|-
| [2020–2030]

| [2020–2025]

|-
| rowspan="2"| '''C3 [311]'''

| rowspan="2"| '''limit warming to 2°C (&gt;67%)'''

| rowspan="2"|
| rowspan="2"| 44

[32–55]

| rowspan="2"| 29

[20–36]

| rowspan="2"| 20

[13–26]

| rowspan="2"| 21

[1–42]

| rowspan="2"| 46

[34–63]

| rowspan="2"| 64

[53–77]

| colspan="2"| 2020–2025 (100%)

| rowspan="2"| 2070–2075 (93%)

[2055–...]

| rowspan="2"| ...–... (30%)

[2075–...]

| rowspan="2"| 890

[640–1160]

| rowspan="2"| 800

[510–1140]

| rowspan="2"| –40

[–290 to 0]

| rowspan="2"| 1.7

[1.6–1.8]

| rowspan="2"| 1.6

[1.5–1.8]

| rowspan="2"| 20

[13–41]

| rowspan="2"| 76

[68–91]

| rowspan="2"| 99

[98–100]

|-
| [2020–2030]

| [2020–2025]

|-
| '''C3a [204]'''

| '''… with action starting in 2020'''

| SSP1–2.6

| 40

[30–49]

| 29

[21–36]

| 20

[14–27]

| 27

[13–45]

| 47

[35–63]

| 63

[52–76]

| colspan="2"| 2020–2025 (100%)

[2020–2025]

| 2070–2075 (91%)

[2055–...]

| ...–... (24%)

[2080–...]

| 860

[640–1180]

| 790

[480–1150]

| –30

[–280 to 0]

| 1.7

[1.6–1.8]

| 1.6

[1.5–1.8]

| 21

[14–42]

| 78

[69–91]

| 100

[98–100]

|-
| '''C3b [97]'''

| '''… NDCs until 2030'''

| GS

| 52

[47–56]

| 29

[20–36]

| 18

[10–25]

| 5

[0–14]

| 46

[34–63]

| 68

[56–82]

| rowspan="3" colspan="2"| 2020–2025 (100%)

[2020–2030]

| 2065–2070 (97%)

[2055–2090]

| ...–... (41%)

[2075–...]

| 910

[720–1150]

| 800

[560–1050]

| –60

[–300 to 0]

| 1.8

[1.6–1.8]

| 1.6

[1.5–1.7]

| 17

[12–35]

| 73

[67–87]

| 99

[98–99]

|-
| '''C4 [159]'''

| '''limit warming to 2°C (&gt;50%)'''

|
| 50

[41–56]

| 38

[28–44]

| 28

[19–35]

| 10

[0–27]

| 31

[20–50]

| 49

[35–65]

| 2080–2085 (86%)

[2065–...]

| ...–... (31%)

[2075–...]

| 1210

[970–1490]

| 1160

[700–1490]

| –30

[–390 to 0]

| 1.9

[1.7–2.0]

| 1.8

[1.5–2.0]

| 11

[7–22]

| 59

[50–77]

| 98

[95–99]

|-
| '''C5 [212]'''

| '''limit warming to 2.5°C (&gt;50%)'''

|
| 52

[46–56]

| 45

[37–53]

| 39

[30–49]

| 6

[–1 to 18]

| 18

[4–33]

| 29

[11–48]

| ...–... (41%)

[2080–...]

| ...–... (12%)

[2090–...]

| 1780

[1400–2360]

| 1780

[1260–2360]

| 0

[–160 to 0]

| 2.2

[1.9–2.5]

| 2.1

[1.9–2.5]

| 4

[0–10]

| 37

[18–59]

| 91

[83–98]

|-
| rowspan="2"| '''C6 [97]'''

| rowspan="2"| '''limit warming to 3°C (&gt;50%)'''

| rowspan="2"| SSP2–4.5

ModAct

| rowspan="2"| 54

[50–62]

| rowspan="2"| 53

[48–61]

| rowspan="2"| 52

[45–57]

| rowspan="2"| 2

[–10 to 11]

| rowspan="2"| 3

[–14 to 14]

| rowspan="2"| 5

[–2 to 18]

| 2030–2035 (96%)

| 2020–2025 (97%)

| rowspan="6" colspan="2"| no net zero

| rowspan="6"| no net zero

| rowspan="2"| 2790

[2440–3520]

| rowspan="6"| no net zero

| rowspan="6"| temperature does not peak by 2100

| rowspan="2"| 2.7

[2.4–2.9]

| rowspan="2"| 0

[0–0]

| rowspan="2"| 8

[2–18]

| rowspan="2"| 71

[53–88]

|-
| colspan="2"| [2020–2090]

|-
| rowspan="2"| '''C7 [164]'''

| rowspan="2"| '''limit warming to 4°C (&gt;50%)'''

| rowspan="2"| SSP3–7.0

CurPol

| rowspan="2"| 62

[53–69]

| rowspan="2"| 67

[56–76]

| rowspan="2"| 70

[58–83]

| rowspan="2"| –11

[–18 to 3]

| rowspan="2"| –19

[–31 to 1]

| rowspan="2"| –24

[–41 to –2]

| 2085–2090 (57%)

| 2090–2095 (56%)

| rowspan="2"| 4220

[3160–5000]

| rowspan="2"| 3.5

[2.8–3.9]

| rowspan="2"| 0

[0–0]

| rowspan="2"| 0

[0–2]

| rowspan="2"| 22

[7–60]

|-
| colspan="2"| [2040–...]

|-
| rowspan="2"| '''C8 [29]'''

| rowspan="2"| '''exceed warming of 4°C (≥50%)'''

| rowspan="2"| SSP5–8.5

| rowspan="2"| 71

[69–81]

| rowspan="2"| 80

[78–96]

| rowspan="2"| 88

[82–112]

| rowspan="2"| –20

[–34 to –17]

| rowspan="2"| –35

[–65 to –29]

| rowspan="2"| –46

[–92 to –36]

| rowspan="2" colspan="2"| 2080–2085 (90%)

[2070–...]

| 5600

| rowspan="2"| 4.2

[3.7–5.0]

| rowspan="2"| 0

[0–0]

| rowspan="2"| 0

[0–0]

| rowspan="2"| 4

[0–11]

|-
| [4910–7450]

|}

a Values in the table refer to the 50th and [5th–95th] percentile values across the pathways falling within a given category as defined in Box SPM.1. For emissions-related columns these values relate to the distribution of all the pathways in that category. Harmonised emissions values are given for consistency with projected global warming outcomes using climate emulators. Based on the assessment of climate emulators in AR6 WGI (WG1 Chapter 7, Box 7.1), two climate emulators are used for the probabilistic assessment of the resulting warming of the pathways. For the ‘Temperature change’ and ‘Likelihood’ columns, the single upper-row values represent the 50th percentile across the pathways in that category and the median [50th percentile] across the warming estimates of the probabilistic MAGICC climate model emulator. For the bracketed ranges, the median warming for every pathway in that category is calculated for each of the two climate model emulators (MAGICC and FaIR). Subsequently, the 5th and 95th percentile values across all pathways for each emulator are calculated. The coolest and warmest outcomes (i.e., the lowest p5 of two emulators, and the highest p95, respectively) are shown in square brackets. These ranges therefore cover both the uncertainty of the emissions pathways as well as the climate emulators’ uncertainty.

b For a description of pathways categories see Box SPM.1 and Table 3.1.

c All global warming levels are relative to 1850–1900. (See footnote n below and Box SPM.1 for more details.)

d C3 pathways are sub-categorised according to the timing of policy action to match the emissions pathways in Figure SPM.4. Two pathways derived from a cost-benefit analysis have been added to C3a, whilst 10 pathways with specifically designed near-term action until 2030, whose emissions fall below those implied by NDCs announced prior to COP26, are not included in either of the two subsets.

e Alignment with the categories of the illustrative SSP scenarios considered in AR6 WGI, and the Illustrative (Mitigation) Pathways (IPs/IMPs) of WGIII. The IMPs have common features such as deep and rapid emissions reductions, but also different combinations of sectoral mitigation strategies. See Box SPM.1 for an introduction of the IPs and IMPs, and [https://www.ipcc.ch/chapters/chapter-3 Chapter 3] for full descriptions. {3.2, 3.3, Annex III.II.4}

f The Illustrative Mitigation Pathway ‘Neg’ has extensive use of carbon dioxide removal (CDR) in the AFOLU, energy and the industry sectors to achieve net negative emissions. Warming peaks around 2060 and declines to below 1.5°C (50% likelihood) shortly after 2100. Whilst technically classified as C3, it strongly exhibits the characteristics of C2 high-overshoot pathways, hence it has been placed in the C2 category. See Box SPM.1 for an introduction of the IPs and IMPs.

g The 2019 range of harmonised GHG emissions across the pathways [53–58 GtCO ''2'' -eq] is within the uncertainty ranges of 2019 emissions assessed in [https://www.ipcc.ch/chapters/chapter-2 Chapter 2] [53–66 GtCO ''2'' -eq]. (Figure SPM.1, Figure SPM.2, Box SPM.1)

h Rates of global emission reduction in mitigation pathways are reported on a pathway-by-pathway basis relative to harmonised modelled global emissions in 2019 rather than the global emissions reported in SPM Section B and Chapter 2; this ensures internal consistency in assumptions about emission sources and activities, as well as consistency with temperature projections based on the physical climate science assessment by WGI. {Annex III.II.2.5} . Negative values (e.g., in C7, C8) represent an increase in emissions.

i Emissions milestones are provided for five-year intervals in order to be consistent with the underlying five-year time-step data of the modelled pathways. Peak emissions (CO 2 and GHGs) are assessed for five-year reporting intervals starting in 2020. The interval 2020–2025 signifies that projected emissions peak as soon as possible between 2020 and at latest before 2025. The upper five-year interval refers to the median interval within which the emissions peak or reach net zero. Ranges in square brackets underneath refer to the range across the pathways, comprising the lower bound of the 5th percentile five-year interval and the upper bound of the 95th percentile five-year interval. Numbers in round brackets signify the fraction of pathways that reach specific milestones.

j Percentiles reported across all pathways in that category include those that do not reach net zero before 2100 (fraction of pathways reaching net zero is given in round brackets). If the fraction of pathways that reach net zero before 2100 is lower than the fraction of pathways covered by a percentile (e.g., 0.95 for the 95th percentile), the percentile is not defined and denoted with ‘…’. The fraction of pathways reaching net zero includes all with reported non-harmonised, and/or harmonised emissions profiles that reach net zero. Pathways were counted when at least one of the two profiles fell below 100 MtCO 2 yr –1 until 2100.

k The timing of net zero is further discussed in SPM C2.4 and Cross-Chapter Box 3 in [https://www.ipcc.ch/chapters/chapter-3 Chapter 3] on net zero CO 2 and net zero GHG emissions.

l For cases where models do not report all GHGs, missing GHG species are infilled and aggregated into a Kyoto basket of GHG emissions in CO 2 -eq defined by the 100-year global warming potential. For each pathway, reporting of CO 2 , CH 4 , and N 2 O emissions was the minimum required for the assessment of the climate response and the assignment to a climate category. Emissions pathways without climate assessment are not included in the ranges presented here. {See Annex III.II.5}

m Cumulative emissions are calculated from the start of 2020 to the time of net zero and 2100, respectively. They are based on harmonised net CO 2 emissions, ensuring consistency with the WGI assessment of the remaining carbon budget. {Box 3.4}

n Global mean temperature change for category (at peak, if peak temperature occurs before 2100, and in 2100) relative to 1850–1900, based on the median global warming for each pathway assessed using the probabilistic climate model emulators calibrated to the AR6 WGI assessment. (See also Box SPM.1) {Annex III.II.2.5; WGI Cross-Chapter Box 7.1}

o Probability of staying below the temperature thresholds for the pathways in each category, taking into consideration the range of uncertainty from the climate model emulators consistent with the AR6 WGI assessment. The probabilities refer to the probability at peak temperature. Note that in the case of temperature overshoot (e.g., category C2 and some pathways in C1), the probabilities of staying below at the end of the century are higher than the probabilities at peak temperature.

'''Pathways accelerating action compared to current NDCs – that reduce annual GHG emissions to 47 (38–51) GtCO''' 2 '''-eq by 2030 (which is 3–9 GtCO''' 2 '''-eq below projected emissions from fully implementing current NDCs) – make it less challenging to limit warming to 2°C (&gt;67%) after 2030 (''' '''''medium confidence''''' ''').''' The accelerated action pathways are characterised by a global, but regionally differentiated, roll-out of regulatory and pricing policies. Compared to current NDCs, they describe less fossil fuel use and more low-carbon fuel use until 2030; they narrow, but do not close the gap to pathways that assume immediate global action using all available least-cost abatement options. All delayed or accelerated action pathways limiting warming to below 2°C (&gt;67%) converge to a global mitigation regime at some point after 2030 by putting a significant value on reducing carbon and other GHG emissions in all sectors and regions. {3.5}

'''In mitigation pathways, peak warming is determined by the cumulative net CO''' 2 '''emissions until the time of net zero CO''' 2 '''together with the warming contribution of other GHGs and climate forcers at that time (''' '''''high confidence''''' ''').''' Cumulative net CO 2 emissions from 2020 to the time of net zero CO 2 are 510 (330–710) GtCO 2 in pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot and 890 (640–1160) GtCO 2 in pathways limiting warming to 2°C (&gt;67%). These estimates are consistent with the AR6 WGI assessment of remaining carbon budgets adjusting for methodological differences and non-CO 2 warming. {3.3, Box 3.4}

'''Rapid reductions in non-CO''' ''2'' '''GHGs, particularly CH''' ''4'' ''', would lower the level of peak warming (''' '''''high confidence''''' ''').''' Non-CO ''2'' emissions – at the time of reaching net zero CO ''2'' – range between 4–11 GtCO ''2'' -eq yr ''–1'' in pathways limiting warming to 2°C (&gt;67%) or below. CH ''4'' is reduced by around 20% (1–46%) in 2030 and almost 50% (26–64%) in 2050, relative to 2019. CH ''4'' emission reductions in pathways limiting warming to 1.5°C with no or limited overshoot are substantially higher by 2030, 33% (19–57%), but only moderately so by 2050, 50% (33–69%). CH ''4'' emissions reductions are thus attainable at comparatively low costs, but, at the same time, reductions are limited in scope in most 1.5°C–2°C pathways. Deeper CH ''4'' emissions reductions by 2050 could further constrain the peak warming. N ''2'' O emissions are also reduced, but similar to CH ''4'' , N ''2'' O emission reductions saturate for more stringent climate goals. The emissions of cooling aerosols in mitigation pathways decrease as fossil fuels use is reduced. The overall impact on non-CO ''2'' -related warming combines all these factors. {3.3}

'''Net zero GHG emissions imply net negative CO''' 2 '''emissions at a level that compensates for residual non-CO''' 2 '''emissions. Only 30% of the pathways limiting warming to 2°C (&gt;67%) or below reach net zero GHG emissions in the 21st century (''' '''''high confidence''''' ''').''' In those pathways reaching net zero GHGs, net zero GHGs is achieved around 10–20 years later than net zero CO 2 is achieved ( ''medium confidence'' ). The reported quantity of residual non-CO 2 emissions depends on accounting choices, and in particular the choice of GHG metric (Box TS.2). Reaching and sustaining global net zero GHG emissions – when emissions are measured and reported in terms of GWP100 – results in a gradual decline in temperature ( ''high confidence'' ). (Box TS.6) {3.3}

'''Pathways that limit warming to 2°C (&gt;67%) or lower exhibit substantial reductions in emissions from all sectors (''' '''''high confidence''''' ''').''' Pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot entail CO 2 emissions reductions between 2019 and 2050 of around 77% (31–96%) for energy demand, around 115% (90–167%) for energy supply, and around 148% (94–387%) for AFOLU. [[#footnote-017|16]] In pathways that limit warming to 2°C (&gt;67%), projected CO 2 emissions are reduced between 2019 and 2050 by around 49% for energy demand, 97% for energy supply, and 136% for AFOLU ( ''medium confidence'' ). {3.4}

'''If warming is to be limited, delaying or failing to achieve emissions reductions in one sector or region necessitates compensating reductions in other sectors or regions (''' '''''high confidence''''' ''').''' Mitigation pathways show differences in the timing of decarbonisation and when net zero CO 2 emissions are achieved across sectors and regions. At the time of ''global net zero CO'' 2 ''emissions'' , emissions in some sectors and regions are positive while others are negative; whether specific sectors and regions are positive or negative depends on the availability and cost of mitigation options in those regions, and the policies implemented. In cost-effective mitigation pathways, the energy supply sector typically reaches net zero CO 2 before the economy as a whole, while the demand sectors reach net zero CO 2 later, if ever ( ''high confidence'' ). (Figure TS.10) {3.4}

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'''Figure TS.10''' ''': Mitigation pathways that limit warming to 1.5°C, or 2°C, involve deep, rapid and sustained emissions reductions. Net zero CO''' 2 '''and net zero GHG emissions are possible through different mitigation portfolios. Panels (a) and (b)''' show the development of global GHG and CO 2 emissions in modelled global pathways (upper sub-panels) and the associated timing of when GHG and CO 2 emissions reach net zero (lower sub-panels). '''Panels (c) and (d)''' show the development of global CH 4 and N 2 O emissions, respectively. Coloured ranges denote the 5th to 95th percentile across pathways. The red ranges depict emissions pathways assuming policies that were implemented by the end of 2020 and pathways assuming implementation of NDCs (announced prior to COP26). Ranges of modelled pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot are shown in light blue (category C1) and pathways that limit warming to 2°C (&gt;67%) are shown in light purple (category C3). The grey range comprises all assessed pathways (C1–C8) from the 5th percentile of the lowest warming category (C1) to the 95th percentile of the highest warming category (C8). The modelled pathway ranges are compared to the emissions from two pathways illustrative of high emissions (CurPol and ModAct) and five IMPs: IMP-LD, IMP-Ren, IMP-SP, IMP-Neg and IMP-GS. Emissions are harmonised to the same 2015 base year. The vertical error bars in 2015 show the 5–95th percentile uncertainty range of the non-harmonised emissions across the pathways, and the uncertainty range, and median value, in emission estimates for 2015 and 2019. The vertical error bars in 2030 (panel a) depict the assessed range of the NDCs, as announced prior to COP26. [[#footnote-016|17]] '''Panel (e)''' shows the sectoral contributions of CO 2 and non-CO 2 emissions sources and sinks at the time when net zero CO 2 emissions are reached in the IMPs. Positive and negative emissions for different IMPs are compared to the GHG emissions from the year 2019. Energy supply (neg.) includes BECCS and DACCS. DACCS features in only two of the five IMPs (IMP-REN and IMP-GS) and contributes &lt;1% and 64%, respectively, to the net negative emissions in Energy Supply (neg.). '''Panel (f)''' shows the contribution of different sectors and sources to the emissions reductions from a 2019 baseline for reaching net zero GHG emissions. Bars denote the median emissions reductions for all pathways that reach net zero GHG emissions. The whiskers indicate the p5–p95 range. The contributions of the service sectors (transport, buildings, industry) are split into direct (demand-side) as well as indirect (supply-side) CO 2 emissions reductions. Direct emissions represent demand-side emissions due to the fuel use in the respective demand sector. Indirect emissions represent upstream emissions due to industrial processes and energy conversion, transmission and distribution. In addition, the contributions from the LULUCF sector and reductions from non-CO 2 emissions sources (green and grey bars) are displayed. {3.3, 3.4}

'''Pathways limiting warming to 2°C (&gt;67%) or 1.5°C involve substantial reductions in fossil fuel consumption and a near elimination of coal use without CCS (''' '''''high confidence''''' ''').''' These pathways show an increase in low-carbon energy, with 88% (69–97%) of primary energy coming from low-carbon sources by 2100. {3.4}

'''Stringent emissions reductions at the level required for 2°C or 1.5°C are achieved through the increased electrification of buildings, transport, and industry, consequently all pathways entail increased electricity generation (''' '''''high confidence''''' ''').''' Nearly all electricity in pathways limiting warming to 2°C (&gt;67%) or 1.5°C (&gt;50%) is also from low- or no-carbon technologies, with different shares across pathways of: nuclear, biomass, non-biomass renewables, and fossil fuels in combination with CCS. {3.4}

'''Measures required to limit warming to 2°C (&gt;67%) or below can result in large-scale transformation of the land surface (''' '''''high confidence''''' ''').''' These pathways are projected to reach net zero CO 2 emissions in the AFOLU sector between the 2020s and 2070.

'''Pathways limiting warming to 1.5°C with no or limited overshoot show an increase in forest cover of about 322 (–67 to 890) million ha in 2050 (''' '''''high confidence''''' ''').''' In these pathways the cropland area to supply biomass for bioenergy (including bioenergy with carbon capture and storage (BECCS)) is around 199 (56–482) million ha in 2050. The use of bioenergy can lead to either increased or reduced emissions, depending on the scale of deployment, conversion technology, fuel displaced, and how, and where, the biomass is produced ( ''high confidence'' ). {3.4}

'''Pathways limiting warming to 2°C (&gt;67%) or 1.5°C (&gt;50%) require some amount of CDR to compensate for residual GHG emissions, even alongside substantial direct emissions reductions are achieved in all sectors and regions (''' '''''high confidence''''' ''').''' CDR deployment in pathways serves multiple purposes: accelerating the pace of emissions reductions, offsetting residual emissions, and creating the option for net negative CO 2 emissions in case temperature reductions need to be achieved in the long term ( ''high confidence'' ). CDR options in pathways are mostly limited to BECCS, afforestation and direct air CO 2 capture and storage (DACCS). CDR through some measures in AFOLU can be maintained for decades but not over the very long term because these sinks will ultimately saturate ( ''high confidence'' ). {3.4}

'''Mitigation pathways show reductions in energy demand, relative to reference scenarios that assume continuation of current policies, through a diverse set of demand-side interventions (''' '''''high confidence''''' ''').''' Bottom-up and non-IAM studies show significant potential for demand-side mitigation. A stronger emphasis on demand-side mitigation implies less dependence on CDR and, consequently, reduced pressure on land and biodiversity. {3.4, 3.7}

'''Limiting warming requires shifting energy investments away from fossil fuels and towards low-carbon technologies (''' '''''high confidence''''' ''').''' The bulk of investments are needed in medium- and low-income regions. Investment needs in the electricity sector are on average 2.3 trillion USD2015 yr –1 over 2023–2052 for pathways limiting temperature to 1.5°C (&gt;50%) with no or limited overshoot, and 1.7 trillion USD2015 yr –1 for pathways limiting warming to 2°C (&gt;67%). {3.6.1}

'''Pathways''' '''''that''''' '''avoid overshoot of 2°C (&gt;67%) warming require more rapid near-term transformations and are associated with higher upfront transition costs, but at the same time bring long-term gains for the economy as well as earlier benefits in avoided climate change impacts (''' '''''high confidence''''' ''').''' This conclusion is independent of the discount rate applied, though the modelled cost-optimal balance of mitigation action over time does depend on the discount rate. Lower discount rates favour earlier mitigation, reducing reliance on CDR and temperature overshoot. {3.6.1, 3.8}

'''Mitigation pathways''' '''''that''''' '''limit warming to 2°C (&gt;67%) entail losses in global GDP with respect to reference scenarios of between 1.3% and 2.7% in 2050. In pathways limiting warming to 1.5°C (&gt;50%) with no or limited overshoot, losses are between 2.6% and 4.2%. These estimates do not account for the economic benefits of avoided climate change impacts (''' '''''medium confidence''''' ''').''' In mitigation pathways limiting warming to 2°C (&gt;67%), marginal abatement costs of carbon are about 90 (60–120) USD2015 tCO 2 in 2030 and about 210 (140–340) USD2015/tCO 2 in 2050. This compares with about 220 (170–290) USD2015 tCO 2 in 2030 and about 630 (430–990) USD2015 tCO 2 in 2050 [[#footnote-015|18]] in pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot. Reference scenarios, in the AR6 scenarios database, describe possible emission trajectories in the absence of new stringent climate policies. Reference scenarios have a broad range depending on socio-economic assumptions and model characteristics. {3.2.1, 3.6.1}

'''The global benefits of pathways limiting warming to 2°C (&gt;67%) outweigh global mitigation costs over the 21st century, if aggregated economic impacts of climate change are at the moderate to high end of the assessed range, and a weight consistent with economic theory is given to economic impacts over the long term. This holds true even without accounting for benefits in other sustainable development dimensions or no''' '''n-mar''' '''ket damages from climate change (''' '''''medium confidence''''' ''').''' The aggregate global economic repercussions of mitigation pathways include: the macroeconomic impacts of investments in low-carbon solutions and structural changes away from emitting activities; co-benefits and adverse side effects of mitigation; avoided climate change impacts; and reduced adaptation costs. Existing quantifications of the global aggregate economic impacts show a strong dependence on socio-economic development conditions, as these shape exposure and vulnerability and adaptation opportunities and responses. Avoided impacts for poorer households and poorer countries represent a smaller share in aggregate economic quantifications expressed in GDP or monetary terms, whereas their well-being and welfare effects are comparatively larger. When aggregate economic benefits from avoided climate change impacts are accounted for, mitigation is a welfare-enhancing strategy ( ''high confidence'' ) ''.'' {3.6.2}

'''The economic benefits on human health from air quality improvement arising from mitigation action can be of the same order of magnitude as mitigation costs, and potentially even larger (''' '''''medium confidence''''' ''').''' {3.6.3}

'''Differences in aggregate employment between mitigation pathways and reference scenarios are relatively small, although there may be substantial reallocations across sectors, with job creation in some sectors and job losses in others (''' '''''medium confidence''''' ''').''' The net employment effect (and whether employment increases or decreases) depends on the scenario assumptions, modelling framework, and modelled policy design. Mitigation has implications for employment through multiple channels, each of which impacts geographies, sectors and skill categories differently. {3.6.4}

'''The economic repercussions of mitigation vary widely across regions and households, depending on policy design and the level of international cooperation (''' '''''high confidence''''' ''').''' Delayed global cooperation increases policy costs across regions, especially in those that are relatively carbon intensive at present ( ''high confidence'' ). Pathways with uniform carbon values show higher mitigation costs in more carbon-intensive regions, in fossil fuel-exporting regions, and in poorer regions ( ''high confidence'' ). Aggregate quantifications expressed in GDP or monetary terms undervalue the economic effects on households in poorer countries; the actual effects on welfare and well-being are comparatively larger ( ''high confidence'' ). Mitigation at the speed and scale required to limit warming to 2°C (&gt;67%) or below implies deep economic and structural changes, thereby raising multiple types of distributional concerns across regions, income classes, and sectors ( ''high confidence'' ). (Box TS.7) {3.6.1, 3.6.4}

'''Box TS.6 |''' '''Understanding Net Zero CO''' 2 '''and Net Zero GHG Emissions'''

Reaching net zero CO 2 emissions [[#footnote-014|19]] globally along with reductions in other GHG emissions is necessary to halt global warming at any level. At the point of net zero, the amount of CO 2 human activity is putting into the atmosphere equals the amount of CO 2 human activity is removing from the atmosphere. Reaching and sustaining net zero CO 2 emissions globally would stabilise CO 2 -induced warming. Moving to net negative CO 2 emissions globally would reduce peak cumulative net CO 2 emissions – which occurs at the time of reaching net zero CO 2 emissions – and lead to a peak and decline in CO 2 -induced warming. {Cross-Chapter Box 3 in Chapter 3}

Reaching net zero CO 2 emissions sooner can reduce cumulative CO 2 emissions and result in less human-induced global warming. Overall human-induced warming depends not only on CO 2 emissions but also on the contribution from other anthropogenic climate forcers, including aerosols and other GHGs (e.g., CH 4 and F-gases). To halt total human-induced warming, emissions of other GHGs, in particular CH 4 , need to be strongly reduced.

In the AR6 scenario database, global emissions pathways limi warming to 1.5°C (&gt;50%) with no or limited overshoot reach net zero CO 2 emissions between 2050–2055 (2035–2070) (median and 5–95th percentile ranges; 100% of pathways); pathways limiting warming to 2°C (&gt;67%) reach net zero CO 2 emissions between 2070–2075 (2055–…) (median and 5–95th percentile ranges; 90% of pathways). This is later than assessed in the AR6 SR1.5 primarily due to more pathways in the literature that approach net zero CO 2 emissions more gradually after a rapid decline of emissions until 2040. (Box TS.6, Figure 1)

[[File:335f0fb8b1f4084630c619f6c7aef8b8 IPCC_AR6_WGIII_Box_TS_6_Figure_1.png]]

'''Box TS.6, Figure''' '''1 |''' '''CO''' 2 '''Emissions (panel (a)) and temperature change (panel (b)) of three alternative pathways limiting warming to 2°C (&gt;67%) and reaching net zero CO''' 2 '''emissions at different points in time.''' Limiting warming to a specific level can be consistent with a range of dates when net zero CO 2 emissions need to be achieved. This difference in the date of net zero CO 2 emissions reflects the different emissions profiles that are possible while staying within a specific carbon budget and the associated warming limit. Shifting the year of net zero to a later point in time (&gt;2050), however, requires more rapid and deeper near-term emissions reductions (in 2030 and 2040) if warming is to be limited to the same level. Funnels show pathways limiting warming to 1.5°C (&gt;50%) with no or limited overshoot (light blue) and limiting warming to 2°C (&gt;67%) (beige).

It does not mean that the world has more time for emissions reductions while still limiting warming to 1.5°C than reported in the SR1.5. It only means that the exact timing of reaching net zero CO 2 after a steep decline of CO 2 emissions until 2040 can show some variation. The SR1.5 median value of 2050 is still close to the middle of the current range. If emissions are reduced less rapidly in the period up to 2030, an earlier net zero year is needed.

Reaching net zero GHG emissions requires net negative CO 2 emissions to balance residual CH ''4'' , N 2 O and F-gas emissions. If achieved globally, net zero GHG emissions would reduce global warming from an earlier peak. Around half global emission pathways limiting warming to 1.5°C (&gt;50%), and a third of pathways limiting warming to 2°C (&gt;67%), reach net zero GHG emissions (based on GWP100) in the second half of the century, around 10 to 40 years later than net zero CO 2 emissions. They show warming being halted at some peak value followed by a gradual decline towards the end of the century. The remainder of the pathways do not reach net zero GHG emissions during the 21st century and show little decline of warming after it stabilised.

Global net zero CO 2 or GHG emissions can be achieved even while some sectors and regions continue to be net emitters, provided that others achieve net GHG removal. Sectors and regions have different potentials and costs to achieve net zero or even net GHG removal. The adoption and implementation of net zero emission targets by countries and regions depends on multiple factors, including equity and capacity criteria and international and cross-sectoral mechanisms to balance emissions and removals. The formulation of net zero pathways by countries will benefit from clarity on scope, plans of action, and fairness. Achieving net zero emission targets relies on policies, institutions and milestones against which to track progress.

'''Box TS.7 | The Long-term Economic Benefits of Mitigation from Avoided Climate Change Impacts'''

Integrated studies use either a cost-effectiveness analysis (CEA) approach (minimising the total mitigation costs of achieving a given policy goal) or a cost-benefit analysis (CBA) approach (balancing the cost and benefits of climate action). In the majority of studies that have produced the body of work on the cost of mitigation assessed in this report, a CEA approach is adopted, and the feedbacks of climate change impacts on the economic development pathways are not accounted for. This omission of climate impacts leads to overly optimistic economic projections in the reference scenarios, in particular in reference scenarios with no or limited mitigation action where the extent of global warming is the greatest. Mitigation cost estimates computed against no or limited policy reference scenarios therefore omit economic benefits brought by avoided climate change impact along mitigation pathways. {1.7, 3.6.1}

The difference in aggregate economic impacts from climate change between two given temperature levels represents the aggregate economic benefits arising from avoided climate change impacts due to mitigation action. Estimates of these benefits vary widely, depending on the methodology used and impacts included, as well as on assumed socio-economic development conditions, which shape exposure and vulnerability. The aggregate economic benefits of avoiding climate impacts increase with the stringency of the mitigation. Global economic impact studies with regional estimates find large differences across regions, with developing and transitional economies typically more vulnerable. Furthermore, avoided impacts for poorer households and poorer countries represent a smaller share in aggregate quantifications expressed in GDP terms or monetary terms, compared to their influence on well-being and welfare ( ''high confidence'' ). {3.6.2, Cross-Working Group Box 1 in Chapter 3}

CBA analysis and CBA integrated assessment models (IAMs) remain limited in their ability to represent all damages from climate change, including non-monetary damages, and capture the uncertain and heterogeneous nature of damages and the risk of catastrophic damages, such that other lines of evidence should be considered in decision-making. However, emerging evidence suggests that, even without accounting for co-benefits of mitigation on other sustainable development dimensions, the global benefits of pathways limiting warming to 2°C (&gt;67%) outweigh global mitigation costs over the 21st century ( ''medium confidence'' ). Depending on the study, the reason for this result lies in assumptions of economic damages from climate change in the higher end of available estimates, in the consideration of risks of tipping points or damages to natural capital and non-market goods, or in the combination of updated representations of carbon cycle and climate modules, updated damage estimates and updated representations of economic and mitigation dynamics. In the studies that perform a sensitivity analysis, this result is found to be robust to a wide range of assumptions on social preferences (in particular on inequality aversion and pure rate of time preference), and holds except if assumptions of economic damages from climate change are in the lower end of available estimates and the pure rate of time preference is in the higher range of values usually considered (typically above 1.5%). However, although such pathways bring overall net benefits over time (in terms of aggregate discounted present value), they involve distributional consequences between and within generations. {3.6.2}

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