Editing IPCC:AR6/SYR/SPM (section)

== B. Future Climate Change, Risks, and Long-Term Responses ==

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=== Future Climate Change ===

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'''B.1 Continued greenhouse gas emissions will lead to increasing global warming, with the best estimate of reaching 1.5°C in the near term in considered scenarios and modelled pathways. Every increment of global warming will intensify multiple and concurrent hazards '''''(high confidence)''''' . Deep, rapid, and sustained reductions in greenhouse gas emissions would lead to a discernible slowdown in global warming within around two decades, and also to discernible changes in atmospheric composition within a few years '''''(high confidence)''''' . [[#figure-spm-2|Figure SPM.2]] [[#box-spm-1|Box SPM.1]] Links to longer report Cross-Section Boxes 1 and 2, 3.1, 3.3, Table 3.1, Figure 3.1, 4.3'''
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B.1.1 Global warming [[#footnote-029|28]] will continue to increase in the near term (2021-2040) mainly due to increased cumulative CO '''2''' emissions in nearly all considered scenarios and modelled pathways. In the near term, global warming ''is more likely'' ''than not'' to reach 1.5°C even under the very low GHG emission scenario (SSP1-1.9) and ''likely'' or ''very likely'' to exceed 1.5°C under higher emissions scenarios. In the considered scenarios and modelled pathways, the best estimates of the time when the level of global warming of 1.5°C is reached lie in the near term [[#footnote-028|29]] . Global warming declines back to below 1.5°C by the end of the 21st century in some scenarios and modelled pathways (see B.7). The assessed climate response to GHG emissions scenarios results in a best estimate of warming for 2081-2100 that spans a range from 1.4°C for a very low GHG emissions scenario (SSP1-1.9) to 2.7°C for an intermediate GHG emissions scenario (SSP2-4.5) and 4.4°C for a very high GHG emissions scenario (SSP5-8.5) [[#footnote-027|30]] , with narrower uncertainty ranges [[#footnote-026|31]] than for corresponding scenarios in AR5. ''[[#box-spm-1|Box SPM.1]] Links to longer report Cross-Section Boxes 1 and 2, 3.1.1, 3.3.4, Table 3.1, 4.3''

B.1.2 Discernible differences in trends of global surface temperature between contrasting GHG emissions scenarios (SSP1-1.9 and SSP1-2.6 vs. SSP3-7.0 and SSP5-8.5) would begin to emerge from natural variability [[#footnote-025|32]] within around 20 years. Under these contrasting scenarios, discernible effects would emerge within years for GHG concentrations, and sooner for air quality improvements, due to the combined targeted air pollution controls and strong and sustained methane emissions reductions. Targeted reductions of air pollutant emissions lead to more rapid improvements in air quality within years compared to reductions in GHG emissions only, but in the long term, further improvements are projected in scenarios that combine efforts to reduce air pollutants as well as GHG emissions [[#footnote-024|33]] . ''(high confidence) Links to longer report 3.1.1''

B.1.3 Continued emissions will further affect all major climate system components. With every additional increment of global warming, changes in extremes continue to become larger. Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation, and very wet and very dry weather and climate events and seasons ''(high confidence)'' . In scenarios with increasing CO 2 emissions, natural land and ocean carbon sinks are projected to take up a decreasing proportion of these emissions ''(high confidence)'' . Other projected changes include further reduced extents and/or volumes of almost all cryospheric elements [[#footnote-023|34]] ''(high confidence)'' , further global mean sea level rise ''(virtually certain)'' , and increased ocean acidification ''(virtually certain)'' and deoxygenation ''(high confidence)'' . ''[[#figure-spm-2|Figure SPM.2]] Links to longer report 3.1.1, 3.3.1, Figure 3.4''

B.1.4 With further warming, every region is projected to increasingly experience concurrent and multiple changes in climatic impact-drivers. Compound heatwaves and droughts are projected to become more frequent, including concurrent events across multiple locations ''(high confidence)'' . Due to relative sea level rise, current 1-in-100 year extreme sea level events are projected to occur at least annually in more than half of all tide gauge locations by 2100 under all considered scenarios ''(high confidence).'' Other projected regional changes include intensification of tropical cyclones and/or extratropical storms ''(medium confidence)'' , and increases in aridity and fire weather ''(medium to high confidence).'' Links to longer report 3.1.1, 3.1.3

B.1.5 Natural variability will continue to modulate human-caused climate changes, either attenuating or amplifying projected changes, with little effect on centennial-scale global warming ''(high confidence)'' . These modulations are important to consider in adaptation planning, especially at the regional scale and in the near term. If a large explosive volcanic eruption were to occur [[#footnote-022|35]] , it would temporarily and partially mask human-caused climate change by reducing global surface temperature and precipitation for one to three years ''(medium confidence)'' . Links to longer report 4.3

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[[File:d6c19f23df611250c8ec8e95d7bf8906 IPCC_AR6_SYR_SPM_Figure2.png]]
'''Figure SPM.2: Projected changes of annual maximum daily maximum temperature, annual mean total column soil moisture and annual maximum 1-day precipitation at global warming levels of 1.5°C, 2°C, 3°C, and 4°C relative to 1850-1900.''' Projected '''(a)''' annual maximum daily temperature change (°C), '''(b)''' annual mean total column soil moisture (standard deviation), '''(c)''' annual maximum 1-day precipitation change (%). The panels show CMIP6 multi-model median changes. In panels (b) and (c), large positive relative changes in dry regions may correspond to small absolute changes. In panel (b), the unit is the standard deviation of interannual variability in soil moisture during 1850-1900. Standard deviation is a widely used metric in characterising drought severity. A projected reduction in mean soil moisture by one standard deviation corresponds to soil moisture conditions typical of droughts that occurred about once every six years during 1850-1900. The WGI Interactive Atlas (https://interactive-atlas.ipcc.ch/) can be used to explore additional changes in the climate system across the range of global warming levels presented in this figure. Links to longer report Figure 3.1, Cross-Section Box.2

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=== Climate Change Impacts and Climate-Related Risks ===

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'''B.2 For any given future warming level, many climate-related risks are higher than assessed in AR5, and projected long-term impacts are up to multiple times higher than currently observed '''''(high confidence)''''' . Risks and projected adverse impacts and related losses and damages from climate change escalate with every increment of global warming '''''(very high confidence)''''' . Climatic and non-climatic risks will increasingly interact, creating compound and cascading risks that are more complex and difficult to manage '''''(high confidence)''''' . [[#figure-spm-3|Figure SPM.3]] [[#figure-spm-4|Figure SPM.4]] Links to longer report Cross-Section Box.2, 3.1, 4.3, Figure 3.3, Figure 4.3'''
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B.2.1 In the near term, every region in the world is projected to face further increases in climate hazards ( ''medium to high confidence'' , depending on region and hazard), increasing multiple risks to ecosystems and humans ''(very high confidence)'' . Hazards and associated risks expected in the near-term include an increase in heat-related human mortality and morbidity ''(high confidence)'' , food-borne, water-borne, and vector-borne diseases ''(high confidence)'' , and mental health challenges [[#footnote-021|36]] ''(very high confidence)'' , flooding in coastal and other low-lying cities and regions ''(high confidence)'' , biodiversity loss in land, freshwater and ocean ecosystems ( ''medium to very high confidence'' , depending on ecosystem), and a decrease in food production in some regions ''(high confidence)'' . Cryosphere-related changes in floods, landslides, and water availability have the potential to lead to severe consequences for people, infrastructure and the economy in most mountain regions ''(high confidence)'' . The projected increase in frequency and intensity of heavy precipitation ''(high confidence)'' will increase rain-generated local flooding ''(medium confidence)'' . ''[[#figure-spm-3|Figure SPM.3]] [[#figure-spm-4|Figure SPM.4]] Links to longer report Figure 3.2, Figure 3.3, 4.3, Figure 4.3''

B.2.2 Risks and projected adverse impacts and related losses and damages from climate change will escalate with every increment of global warming ''(very high confidence)'' . They are higher for global warming of 1.5°C than at present, and even higher at 2°C ( ''high confidence)'' . Compared to the AR5, global aggregated risk levels [[#footnote-020|37]] (Reasons for Concern [[#footnote-019|38]] ) are assessed to become high to very high at lower levels of global warming due to recent evidence of observed impacts, improved process understanding, and new knowledge on exposure and vulnerability of human and natural systems, including limits to adaptation ''(high confidence)'' . Due to unavoidable sea level rise (see also B.3), risks for coastal ecosystems, people and infrastructure will continue to increase beyond 2100 ''(high confidence)'' . ''[[#figure-spm-3|Figure SPM.3]] [[#figure-spm-4|Figure SPM.4]] Links to longer report 3.1.2, 3.1.3, Figure 3.4, Figure 4.3''

B.2.3 With further warming, climate change risks will become increasingly complex and more difficult to manage. Multiple climatic and non-climatic risk drivers will interact, resulting in compounding overall risk and risks cascading across sectors and regions. Climate-driven food insecurity and supply instability, for example, are projected to increase with increasing global warming, interacting with non-climatic risk drivers such as competition for land between urban expansion and food production, pandemics and conflict. ''(high confidence) Links to longer report 3.1.2, 4.3, Figure 4.3''

B.2.4 For any given warming level, the level of risk will also depend on trends in vulnerability and exposure of humans and ecosystems. Future exposure to climatic hazards is increasing globally due to socio-economic development trends including migration, growing inequality and urbanisation. Human vulnerability will concentrate in informal settlements and rapidly growing smaller settlements. In rural areas vulnerability will be heightened by high reliance on climate-sensitive livelihoods. Vulnerability of ecosystems will be strongly influenced by past, present, and future patterns of unsustainable consumption and production, increasing demographic pressures, and persistent unsustainable use and management of land, ocean, and water. Loss of ecosystems and their services has cascading and long-term impacts on people globally, especially for Indigenous Peoples and local communities who are directly dependent on ecosystems, to meet basic needs. ''(high confidence)'' Links to longer report Cross-Section Box.2, Figure 1c, 3.1.2, 4.3

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[[File:f23b9b532c04195ecc0112f32f69a655 IPCC_AR6_SYR_SPM_Figure3.png]]
'''Figure SPM.3:''' Projected risks and impacts of climate change on natural and human systems at different global warming levels (GWLs) relative to 1850-1900 levels. Projected risks and impacts shown on the maps are based on outputs from different subsets of Earth system and impact models that were used to project each impact indicator without additional adaptation. WGII provides further assessment of the impacts on human and natural systems using these projections and additional lines of evidence. '''(a)''' Risks of species losses as indicated by the percentage of assessed species exposed to potentially dangerous temperature conditions, as defined by conditions beyond the estimated historical (1850-2005) maximum mean annual temperature experienced by each species, at GWLs of 1.5°C, 2°C,3°C and 4°C. Underpinning projections of temperature are from 21 Earth system models and do not consider extreme events impacting ecosystems such as the Arctic. '''(b)''' Risks to human health as indicated by the days per year of population exposure to hyperthermic conditions that pose a risk of mortality from surface air temperature and humidity conditions for historical period (1991-2005) and at GWLs of 1.7°C–2.3°C (mean = 1.9°C; 13 climate models), 2.4°C–3.1°C (2.7°C; 16 climate models) and 4.2°C–5.4°C (4.7°C; 15 climate models). Interquartile ranges of GWLs by 2081-2100 under RCP2.6, RCP4.5 and RCP8.5. The presented index is consistent with common features found in many indices included within WGI and WGII assessments. '''(c)''' Impacts on food production: (c1) Changes in maize yield by 2080-2099 relative to 1986-2005 at projected GWLs of 1.6°C–2.4°C (2.0°C), 3.3°C–4.8°C (4.1°C) and 3.9°C–6.0°C (4.9°C). Median yield changes from an ensemble of 12 crop models, each driven by bias-adjusted outputs from 5 Earth system models, from the Agricultural Model Intercomparison and Improvement Project (AgMIP) and the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP). Maps depict 2080-2099 compared to 1986-2005 for current growing regions (&gt;10 ha), with the corresponding range of future global warming levels shown under SSP1-2.6, SSP3-7.0 and SSP5-8.5, respectively. Hatching indicates areas where &lt;70% of the climate-crop model combinations agree on the sign of impact. (c2) Change in maximum fisheries catch potential by 2081-2099 relative to 1986-2005 at projected GWLs of 0.9°C–2.0°C (1.5°C) and 3.4°C–5.2°C (4.3°C). GWLs by 2081-2100 under RCP2.6 and RCP8.5. Hatching indicates where the two climate-fisheries models disagree in the direction of change. Large relative changes in low yielding regions may correspond to small absolute changes. Biodiversity and fisheries in Antarctica were not analysed due to data limitations. Food security is also affected by crop and fishery failures not presented here. ''[[#box-spm-1|Box SPM.1]] Links to longer report 3.1.2, Figure 3.2, Cross-Section Box.2''

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[[File:64894b287e097f7b7218075ce4542ee3 IPCC_AR6_SYR_SPM_Figure4.png]]
'''Figure SPM.4: Subset of assessed climate outcomes and associated global and regional climate risks.''' The burning embers result from a literature based expert elicitation. '''Panel (a): Left''' – Global surface temperature changes in °C relative to 1850-1900. These changes were obtained by combining CMIP6 model simulations with observational constraints based on past simulated warming, as well as an updated assessment of equilibrium climate sensitivity. ''Very'' ''likely'' ranges are shown for the low and high GHG emissions scenarios (SSP1-2.6 and SSP3-7.0) (Cross-Section Box.2). '''Right''' – Global Reasons for Concern (RFC), comparing AR6 (thick embers) and AR5 (thin embers) assessments. Risk transitions have generally shifted towards lower temperatures with updated scientific understanding. Diagrams are shown for each RFC, assuming low to no adaptation. Lines connect the midpoints of the transitions from moderate to high risk across AR5 and AR6. '''Panel (b)''' : Selected global risks for land and ocean ecosystems, illustrating general increase of risk with global warming levels with low to no adaptation. '''Panel (c): Left''' - Global mean sea level change in centimetres, relative to 1900. The historical changes (black) are observed by tide gauges before 1992 and altimeters afterwards. The future changes to 2100 (coloured lines and shading) are assessed consistently with observational constraints based on emulation of CMIP, ice-sheet, and glacier models, and ''likely'' ranges are shown for SSP1-2.6 and SSP3-7.0. '''Right''' - Assessment of the combined risk of coastal flooding, erosion and salinization for four illustrative coastal geographies in 2100, due to changing mean and extreme sea levels, under two response scenarios, with respect to the SROCC baseline period (1986-2005). The assessment does not account for changes in extreme sea level beyond those directly induced by mean sea level rise; risk levels could increase if other changes in extreme sea levels were considered (e.g., due to changes in cyclone intensity). “No-to-moderate response” describes efforts as of today (i.e., no further significant action or new types of actions). “Maximum potential response” represent a combination of responses implemented to their full extent and thus significant additional efforts compared to today, assuming minimal financial, social and political barriers. (In this context, ‘today’ refers to 2019.) The assessment criteria include exposure and vulnerability, coastal hazards, in-situ responses and planned relocation. Planned relocation refers to managed retreat or resettlements. The term response is used here instead of adaptation because some responses, such as retreat, may or may not be considered to be adaptation. '''Panel (d)''' : Selected risks under different socio-economic pathways, illustrating how development strategies and challenges to adaptation influence risk. '''Left''' - Heat-sensitive human health outcomes under three scenarios of adaptation effectiveness. The diagrams are truncated at the nearest whole ºC within the range of temperature change in 2100 under three SSP scenarios. '''Right''' - Risks associated with food security due to climate change and patterns of socio-economic development. Risks to food security include availability and access to food, including population at risk of hunger, food price increases and increases in disability adjusted life years attributable to childhood underweight. Risks are assessed for two contrasted socio-economic pathways (SSP1 and SSP3) excluding the effects of targeted mitigation and adaptation policies. ''[[#box-spm-1|Box SPM.1]] Links to longer report Figure 3.3''

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=== Likelihood and Risks of Unavoidable, Irreversible or Abrupt Changes ===

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'''B.3 Some future changes are unavoidable and/or irreversible but can be limited by deep, rapid and sustained global greenhouse gas emissions reduction. The likelihood of abrupt and/or irreversible changes increases with higher global warming levels. Similarly, the probability of low-likelihood outcomes associated with potentially very large adverse impacts increases with higher global warming levels. ''(high confidence)'' Links to longer report3.1'''
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B.3.1 Limiting global surface temperature does not prevent continued changes in climate system components that have multi-decadal or longer timescales of response ''(high confidence).'' Sea level rise is unavoidable for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and sea levels will remain elevated for thousands of years ''(high confidence)'' . However, deep, rapid and sustained GHG emissions reductions would limit further sea level rise acceleration and projected long-term sea level rise commitment. Relative to 1995-2014, the ''likely'' global mean sea level rise under the SSP1-1.9 GHG emissions scenario is 0.15–0.23 m by 2050 and 0.28–0.55 m by 2100; while for the SSP5-8.5 GHG emissions scenario it is 0.20–0.29 m by 2050 and 0.63–1.01 m by 2100 ''(medium confidence)'' . Over the next 2000 years, global mean sea level will rise by about 2–3 m if warming is limited to 1.5°C and 2–6 m if limited to 2°C ''(low confidence)'' . ''[[#box-spm-1|Box SPM.1]] Links to longer report 3.1.3, Figure 3.4''

B.3.2 The likelihood and impacts of abrupt and/or irreversible changes in the climate system, including changes triggered when tipping points are reached, increase with further global warming ''(high confidence)'' . As warming levels increase, so do the risks of species extinction or irreversible loss of biodiversity in ecosystems including forests ''(medium confidence)'' , coral reefs ''(very high confidence)'' and in Arctic regions ''(high confidence)'' . At sustained warming levels between 2°C and 3°C, the Greenland and West Antarctic ice sheets will be lost almost completely and irreversibly over multiple millennia, causing several metres of sea level rise ''(limited evidence)'' . The probability and rate of ice mass loss increase with higher global surface temperatures ''(high confidence)'' . Links to longer report 3.1.2, 3.1.3

B.3.3 The probability of low-likelihood outcomes associated with potentially very large impacts increases with higher global warming levels ''(high confidence)'' . Due to deep uncertainty linked to ice-sheet processes, global mean sea level rise above the ''likely'' range – approaching 2 m by 2100 and in excess of 15 m by 2300 under the very high GHG emissions scenario (SSP5-8.5) ''(low confidence)'' – cannot be excluded. There is ''medium confidence'' that the Atlantic Meridional Overturning Circulation will not collapse abruptly before 2100, but if it were to occur, it would ''very'' ''likely'' cause abrupt shifts in regional weather patterns, and large impacts on ecosystems and human activities. ''[[#box-spm-1|Box SPM.1]] Links to longer report 3.1.3''

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=== Adaptation Options and their Limits in a Warmer World ===

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'''B.4 Adaptation options that are feasible and effective today will become constrained and less effective with increasing global warming. With increasing global warming, losses and damages will increase and additional human and natural systems will reach adaptation limits. Maladaptation can be avoided by flexible, multi-sectoral, inclusive, long-term planning and implementation of adaptation actions, with co-benefits to many sectors and systems. ''(high confidence)'' ''Links to longer report 3.2, 4.1, 4.2, 4.3'''''
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B.4.1 The effectiveness of adaptation, including ecosystem-based and most water-related options, will decrease with increasing warming. The feasibility and effectiveness of options increase with integrated, multi-sectoral solutions that differentiate responses based on climate risk, cut across systems and address social inequities. As adaptation options often have long implementation times, long-term planning increases their efficiency. ''(high confidence) Links to longer report 3.2, Figure 3.4, 4.1, 4.2''

B.4.2 With additional global warming, limits to adaptation and losses and damages, strongly concentrated among vulnerable populations, will become increasingly difficult to avoid ''(high confidence)'' . Above 1.5°C of global warming, limited freshwater resources pose potential hard adaptation limits for small islands and for regions dependent on glacier and snow melt ''(medium confidence)'' . Above that level, ecosystems such as some warm-water coral reefs, coastal wetlands, rainforests, and polar and mountain ecosystems will have reached or surpassed hard adaptation limits and as a consequence, some Ecosystem-based Adaptation measures will also lose their effectiveness ''(high confidence)'' . Links to longer report 2.3.2, 3.2, 4.3

B.4.3 Actions that focus on sectors and risks in isolation and on short-term gains often lead to maladaptation over the long-term, creating lock-ins of vulnerability, exposure and risks that are difficult to change. For example, seawalls effectively reduce impacts to people and assets in the short-term but can also result in lock-ins and increase exposure to climate risks in the long-term unless they are integrated into a long-term adaptive plan. Maladaptive responses can worsen existing inequities especially for Indigenous Peoples and marginalised groups and decrease ecosystem and biodiversity resilience. Maladaptation can be avoided by flexible, multi-sectoral, inclusive, long-term planning and implementation of adaptation actions, with co-benefits to many sectors and systems. ''(high confidence) Links to longer report 2.3.2, 3.2''

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=== Carbon Budgets and Net Zero Emissions ===

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'''B.5 Limiting human-caused global warming requires net zero CO '''''2''''' emissions. Cumulative carbon emissions until the time of reaching net zero CO '''''2''''' emissions and the level of greenhouse gas emission reductions this decade largely determine whether warming can be limited to 1.5°C or 2°C '''''(high confidence)''''' . Projected CO '''''2''''' emissions from existing fossil fuel infrastructure without additional abatement would exceed the remaining carbon budget for 1.5°C (50%) '''''(high confidence)''''' . Links to longer report 2.3, 3.1, 3.3, Table 3.1'''
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B.5.1 From a physical science perspective, limiting human-caused global warming to a specific level requires limiting cumulative CO '''2''' emissions, reaching at least net zero CO '''2''' emissions, along with strong reductions in other greenhouse gas emissions. Reaching net zero GHG emissions primarily requires deep reductions in CO '''''2''''' , methane, and other GHG emissions, and implies net-negative CO '''2''' emissions [[#footnote-018|39]] . Carbon dioxide removal (CDR) will be necessary to achieve net-negative CO '''''2''''' emissions (see B.6). Net zero GHG emissions, if sustained, are projected to result in a gradual decline in global surface temperatures after an earlier peak. ''(high confidence) Links to longer report 3.1.1, 3.3.1, 3.3.2, 3.3.3, Table 3.1, Cross-Section Box.1''

B.5.2 For every 1000 GtCO '''2''' emitted by human activity, global surface temperature rises by 0.45°C (best estimate, with a ''likely'' range from 0.27°C to 0.63°C). The best estimates of the remaining carbon budgets from the beginning of 2020 are 500 GtCO '''2''' for a 50% likelihood of limiting global warming to 1.5°C and 1150 GtCO '''2''' for a 67% likelihood of limiting warming to 2°C [[#footnote-017|40]] . The stronger the reductions in non-CO '''2''' emissions the lower the resulting temperatures are for a given remaining carbon budget or the larger remaining carbon budget for the same level of temperature change [[#footnote-016|41]] . Links to longer report 3.3.1

B.5.3 If the annual CO '''2''' emissions between 2020-2030 stayed, on average, at the same level as 2019, the resulting cumulative emissions would almost exhaust the remaining carbon budget for 1.5°C (50%), and deplete more than a third of the remaining carbon budget for 2°C (67%). Estimates of future CO '''2''' emissions from existing fossil fuel infrastructures without additional abatement [[#footnote-015|42]] already exceed the remaining carbon budget for limiting warming to 1.5°C (50%) ''(high confidence)'' . Projected cumulative future CO '''2''' emissions over the lifetime of existing and planned fossil fuel infrastructure, if historical operating patterns are maintained and without additional abatement [[#footnote-014|43]] , are approximately equal to the remaining carbon budget for limiting warming to 2°C with a likelihood of 83% [[#footnote-013|44]] ''(high confidence)'' . Links to longer report 2.3.1, 3.3.1, Figure 3.5

B.5.4 Based on central estimates only, historical cumulative net CO '''2''' emissions between 1850 and 2019 amount to about four-fifths [[#footnote-012|45]] of the total carbon budget for a 50% probability of limiting global warming to 1.5°C (central estimate about 2900 GtCO '''2''' ), and to about two thirds [[#footnote-011|46]] of the total carbon budget for a 67% probability to limit global warming to 2°C (central estimate about 3550 GtCO '''2''' ). Links to longer report 3.3.1, Figure 3.5

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=== Mitigation Pathways ===

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'''B.6 All global modelled pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot, and those that limit warming to 2°C (&gt;67%), involve rapid and deep and, in most cases, immediate greenhouse gas emissions reductions in all sectors this decade. Global net zero CO '''''2''''' emissions are reached for these pathway categories, in the early 2050s and around the early 2070s, respectively. '''''(high confidence)''''' [[#figure-spm-5|Figure SPM.5]] [[#box-spm-1|Box SPM.1]] Links to longer report 3.3, 3.4, 4.1, 4.5, Table 3.1'''
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B.6.1 Global modelled pathways provide information on limiting warming to different levels; these pathways, particularly their sectoral and regional aspects, depend on the assumptions described in Box SPM.1. Global modelled pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot or limit warming to 2°C (&gt;67%) are characterized by deep, rapid and, in most cases, immediate GHG emissions reductions. Pathways that limit warming to 1.5C (&gt;50%) with no or limited overshoot reach net zero CO '''2''' in the early 2050s, followed by net negative CO '''2''' emissions. Those pathways that reach net zero GHG emissions do so around the 2070s. Pathways that limit warming to 2C (&gt;67%) reach net zero CO '''2''' emissions in the early 2070s. Global GHG emissions are projected to peak between 2020 and at the latest before 2025 in global modelled pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot and in those that limit warming to 2°C (&gt;67%) and assume immediate action. ''(high confidence) [[#table-spm-1|Table SPM.1]] Links to longer report 3.3.2, 3.3.4, 4.1, Table 3.1, Figure 3.6''

'''Table SPM.1:''' Greenhouse gas and CO 2 emission reductions from 2019, median and 5-95 percentiles. Links to longer report 3.3.1, 4.1, Table 3.1, Figure 2.5, Box SPM.1

{| class="wikitable"
|-
|
| colspan="4"| Reductions from 2019 emission levels (%)

|-
|
| 2030

| 2035

| 2040

| 2050

|-
| rowspan="2"| Limit warming to1.5°C (&gt;50%) with no or limited overshoot

| GHS

| 43 [34-60]

| 60 [49-77]

| 69 [58-90]

| 84 [73-98]

|-
| CO 2

| 48 [36-69]

| 65 [50-96]

| 80 [61-109]

| 99 [79-119]

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

| GHG

| 21 [1-42]

| 35 [22-55]

| 46 [34-63]

| 64 [53-77]

|-
| CO 2

| 22 [1-44]

| 37 [21-59]

| 51 [36-70]

| 73 [55-90]

|}

B.6.2 Reaching net zero CO 2 or GHG emissions primarily requires deep and rapid reductions in gross emissions of CO 2 , as well as substantial reductions of non-CO 2 GHG emissions ''(high confidence)'' . For example, in modelled pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot, global methane emissions are reduced by 34 [21–57] % by 2030 relative to 2019. However, some hard-to-abate residual GHG emissions (e.g., some emissions from agriculture, aviation, shipping, and industrial processes) remain and would need to be counterbalanced by deployment of CDR methods to achieve net zero CO 2 or GHG emissions ''(high confidence)'' . As a result, net zero CO 2 is reached earlier than net zero GHGs ''(high confidence)'' . ''[[#figure-spm-5|Figure SPM.5]] Links to longer report 3.3.2, 3.3.3, Table 3.1, Figure 3.5''

B.6.3 Global modelled mitigation pathways reaching net zero CO 2 and GHG emissions include transitioning from fossil fuels without carbon capture and storage (CCS) to very low- or zero-carbon energy sources, such as renewables or fossil fuels with CCS, demand-side measures and improving efficiency, reducing non-CO 2 GHG emissions, and, and CDR [[#footnote-010|47]] . In most global modelled pathways, land-use change and forestry (via reforestation and reduced deforestation) and the energy supply sector reach net zero CO 2 emissions earlier than the buildings, industry and transport sectors. ''(high confidence)'' ''[[#figure-spm-5|Figure SPM.5]] [[#box-spm-1|Box SPM.1]] Links to longer report 3.3.3, 4.1, 4.5, Figure 4.1''

B.6.4 Mitigation options often have synergies with other aspects of sustainable development, but some options can also have trade-offs. There are potential synergies between sustainable development and, for instance, energy efficiency and renewable energy. Similarly, depending on the context [[#footnote-009|48]] , biological CDR methods like reforestation, improved forest management, soil carbon sequestration, peatland restoration and coastal blue carbon management can enhance biodiversity and ecosystem functions, employment and local livelihoods. However, afforestation or production of biomass crops can have adverse socio-economic and environmental impacts, including on biodiversity, food and water security, local livelihoods and the rights of Indigenous Peoples, especially if implemented at large scales and where land tenure is insecure. Modelled pathways that assume using resources more efficiently or that shift global development towards sustainability include fewer challenges, such as less dependence on CDR and pressure on land and biodiversity. ''(high confidence) Links to longer report 3.4.1''

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[[File:66948f8b8e8ce93ed3e90b41422b4146 IPCC_AR6_SYR_SPM_Figure5.png]]
'''Figure SPM.5: Global emissions pathways consistent with implemented policies and mitigation strategies. Panels (a), (b)''' and '''(c)''' show the development of global GHG, CO '''2''' and methane emissions in modelled pathways, while '''panel (d)''' shows the associated timing of when GHG and CO '''2''' emissions reach net zero. Coloured ranges denote the 5th to 95th percentile across the global modelled pathways falling within a given category as described in Box SPM.1. The red ranges depict emissions pathways assuming policies that were implemented by the end of 2020. 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 green (category C3). Global emission pathways that would limit warming to 1.5°C (&gt;50%) with no or limited overshoot and also reach net zero GHG in the second half of the century do so between 2070-2075. '''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 illustrative mitigation pathways (IMPs) consistent with limiting warming to 1.5°C with a high reliance on net negative emissions (IMP-Neg) (“high overshoot”), high resource efficiency (IMP-LD), a focus on sustainable development (IMP-SP), renewables (IMP-Ren) and limiting warming to 2°C with less rapid mitigation initially followed by a gradual strengthening (IMP-GS). Positive and negative emissions for different IMPs are compared to GHG emissions from the year 2019. Energy supply (including electricity) includes bioenergy with carbon dioxide capture and storage and direct air carbon dioxide capture and storage. CO 2 emissions from land-use change and forestry can only be shown as a net number as many models do not report emissions and sinks of this category separately ''. [[#box-spm-1|Box SPM.1]] Links to longer report Figure 3.6, 4.1''

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=== Overshoot: Exceeding a Warming Level and Returning ===

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'''B.7 If warming exceeds a specified level such as 1.5°C, it could gradually be reduced again by achieving and sustaining net negative global CO '''''2''''' emissions. This would require additional deployment of carbon dioxide removal, compared to pathways without overshoot, leading to greater feasibility and sustainability concerns. Overshoot entails adverse impacts, some irreversible, and additional risks for human and natural systems, all growing with the magnitude and duration of overshoot. '''''(high confidence)''''' Links to longer report 3.1, 3.3, 3.4, Table 3.1, Figure 3.6'''
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B.7.1 Only a small number of the most ambitious global modelled pathways limit global warming to 1.5°C (&gt;50%) by 2100 without exceeding this level temporarily. Achieving and sustaining net negative global CO 2 emissions, with annual rates of CDR greater than residual CO 2 emissions, would gradually reduce the warming level again ''(high confidence)'' . Adverse impacts that occur during this period of overshoot and cause additional warming via feedback mechanisms, such as increased wildfires, mass mortality of trees, drying of peatlands, and permafrost thawing, weakening natural land carbon sinks and increasing releases of GHGs would make the return more challenging ''(medium confidence)'' . ''[[#box-spm-1|Box SPM.1]] Links to longer report 3.3.2, 3.3.4, Table 3.1, Figure 3.6''

B.7.2 The higher the magnitude and the longer the duration of overshoot, the more ecosystems and societies are exposed to greater and more widespread changes in climatic impact-drivers, increasing risks for many natural and human systems. Compared to pathways without overshoot, societies would face higher risks to infrastructure, low-lying coastal settlements, and associated livelihoods. Overshooting 1.5°C will result in irreversible adverse impacts on certain ecosystems with low resilience, such as polar, mountain, and coastal ecosystems, impacted by ice-sheet, glacier melt, or by accelerating and higher committed sea level rise. ''(high confidence) Links to longer report 3.1.2, 3.3.4''

B.7.3 The larger the overshoot, the more net negative CO 2 emissions would be needed to return to 1.5°C by 2100. Transitioning towards net zero CO 2 emissions faster and reducing non-CO 2 emissions such as methane more rapidly would limit peak warming levels and reduce the requirement for net negative CO 2 emissions, thereby reducing feasibility and sustainability concerns, and social and environmental risks associated with CDR deployment at large scales. ''(high confidence)'' Links to longer report 3.3.3, 3.3.4, 3.4.1, Table 3.1

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