Editing IPCC:AR6/WGI/SPM (section)

== B. Possible Climate Futures ==

<div id="h1-3-siblings" class="h1-siblings"></div>

''''A set of five new illustrative emissions scenarios is considered consistently across this Report to explore the climate response to a broader range of greenhouse gas (GHG), land-use and air pollutant futures than assessed in AR5. This set of scenarios drives climate model projections of changes in the climate system. These projections account for solar activity and background forcing from volcanoes. Results over the 21st century are provided for the near term (2021–2040), mid-term (2041–2060) and long term (2081–2100) relative to 1850–1900, unless otherwise stated.''''

<div id="box-spm-1" class="h2-container box-container"></div>

<div id="reamore-spmbox" class="Body-copy_Boxes_Blue-Boxes_•-Box-heading spmbox-heading"></div>

Box SPM.1 | Scenarios, Climate Models and Projections Expand

<div id="spmbulletcont-spmbox" class="spmbulletcont spmbox"></div>

''Box SPM.1.1:'' This Report assesses the climate response to five illustrative scenarios that cover the range of possible future development of anthropogenic drivers of climate change found in the literature. They start in 2015, and include scenarios <sup>[[#footnote-027|22]]</sup> with high and very high GHG emissions (SSP3-7.0 and SSP5-8.5) and CO <sub>2</sub> emissions that roughly double from current levels by 2100 and 2050, respectively, scenarios with intermediate GHG emissions (SSP2-4.5) and CO <sub>2</sub> emissions remaining around current levels until the middle of the century, and scenarios with very low and low GHG emissions and CO <sub>2</sub> emissions declining to net zero around or after 2050, followed by varying levels of net negative CO <sub>2</sub> emissions <sup>[[#footnote-026|23]]</sup> (SSP1-1.9 and SSP1-2.6), as illustrated in Figure SPM.4. Emissions vary between scenarios depending on socio-economic assumptions, levels of climate change mitigation and, for aerosols and non-methane ozone precursors, air pollution controls. Alternative assumptions may result in similar emissions and climate responses, but the socio-economic assumptions and the feasibility or likelihood of individual scenarios are not part of the assessment.   Links to chapters 1.6, Cross-Chapter Box 1.4, TS.1.3 [[#figure-spm-4|Figure SPM.4]]

''Box SPM.1.2:'' This Report assesses results from climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) of the World Climate Research Programme. These models include new and better representations of physical, chemical and biological processes, as well as higher resolution, compared to climate models considered in previous IPCC assessment reports. This has improved the simulation of the recent mean state of most large-scale indicators of climate change and many other aspects across the climate system. Some differences from observations remain, for example in regional precipitation patterns. The CMIP6 historical simulations assessed in this Report have an ensemble mean global surface temperature change within 0.2°C of the observations over most of the historical period, and observed warming is within the ''very likely'' range of the CMIP6 ensemble. However, some CMIP6 models simulate a warming that is either above or below the assessed ''very likely'' range of observed warming.   Links to chapters 1.5, Cross-Chapter Box 2.2, 3.3, 3.8, TS.1.2, Cross-Section Box TS.1 [[#figure-spm-1|Figure SPM.1b]] , [[#figure-spm-2|Figure SPM.2]]

''Box SPM.1.3:'' The CMIP6 models considered in this Report have a wider range of climate sensitivity than in CMIP5 models and the AR6 assessed ''very likely'' range, which is based on multiple lines of evidence. These CMIP6 models also show a higher average climate sensitivity than CMIP5 and the AR6 assessed best estimate. The higher CMIP6 climate sensitivity values compared to CMIP5 can be traced to an amplifying cloud feedback that is larger in CMIP6 by about 20%.   Links to chapters Box 7.1, 7.3, 7.4, 7.5, TS.3.2

''Box SPM.1.4:'' For the first time in an IPCC report, assessed future changes in global surface temperature, ocean warming and sea level are constructed by combining multi-model projections with observational constraints based on past simulated warming, as well as the AR6 assessment of climate sensitivity. For other quantities, such robust methods do not yet exist to constrain the projections. Nevertheless, robust projected geographical patterns of many variables can be identified at a given level of global warming, common to all scenarios considered and independent of timing when the global warming level is reached.   Links to chapters 1.6, 4.3, 4.6, Box 4.1, 7.5, 9.2, 9.6, Cross-Chapter Box 11.1, Cross-Section Box TS.1

Box SPM.1

<div id="figure-spm-4" class="_idGenObjectLayout-1 Body-copy_Boxes_Blue-Boxes_•-Box-extract"></div>

[[File:6c8ac5f6596b4498d936338bff2e7991 IPCC_AR6_WGI_SPM_Figure_4.png]]
'''Figure SPM.4 |''' '''Future anthropogenic emissions of key drivers of climate change and warming contributions by groups of drivers for the five illustrative scenarios used in this report. The five scenarios are SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5.'''

''Panel (a) Annual anthropogenic (human-caused) emissions over the 2015–2100 period.'' Shown are emissions trajectories for carbon dioxide (CO <sub>2</sub> ) from all sectors (GtCO <sub>2</sub> /yr) (left graph) and for a subset of three key non-CO <sub>2</sub> drivers considered in the scenarios: methane (CH <sub>4</sub> , MtCH <sub>4</sub> /yr, top-right graph); nitrous oxide (N <sub>2</sub> O, MtN <sub>2</sub> O/yr, middle-right graph); and sulphur dioxide (SO <sub>2</sub> , MtSO <sub>2</sub> /yr, bottom-right graph, contributing to anthropogenic aerosols in panel (b).

''Panel (b) Warming contributions by groups of anthropogenic drivers and by scenario are shown as the change in global surface temperature (°C)'' in 2081–2100 relative to 1850–1900, with indication of the observed warming to date. Bars and whiskers represent median values and the ''very likely'' range, respectively. Within each scenario bar plot, the bars represent: total global warming (°C; ‘total’ bar) (see Table SPM.1); warming contributions (°C) from changes in CO <sub>2</sub> (‘CO <sub>2</sub> ’ bar) and from non-CO <sub>2</sub> greenhouse gases (GHGs; ‘non-CO <sub>2</sub> GHGs’ bar: comprising well-mixed greenhouse gases and ozone); and net cooling from other anthropogenic drivers (‘aerosols and land use’ bar: anthropogenic aerosols, changes in reflectance due to land-use and irrigation changes, and contrails from aviation) (see Figure SPM.2, panel c, for the warming contributions to date for individual drivers). The best estimate for observed warming in 2010–2019 relative to 1850–1900 (see Figure SPM.2, panel a) is indicated in the darker column in the ‘total’ bar. Warming contributions in panel (b) are calculated as explained in Table SPM.1 for the total bar. For the other bars, the contribution by groups of drivers is calculated with a physical climate emulator of global surface temperature that relies on climate sensitivity and radiative forcing assessments.   Links to chapters Cross-Chapter Box 1.4, 4.6, Figure 4.35, 6.7, Figures 6.18, 6.22 and 6.24, 7.3, Cross-Chapter Box 7.1, Figure 7.7, Box TS.7, Figures TS.4 and TS.15

'''B.1 Global surface temperature will continue to increase until at least mid-century under all emissions scenarios considered. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in CO <sub>2</sub> and other greenhouse gas emissions occur in the coming decades.   Expand [[#figure-spm-1|Figures SPM.1]] , [[#figure-spm-4|SPM.4]] [[#figure-spm-8|SPM.8]] [[#table-spm-1|Table SPM.1]] [[#box-spm-1|Box SPM.1]] Links to chapters 2.3, Cross-Chapter Box 2.3, Cross-Chapter Box 2.4, 4.3, 4.4, 4.5'''
<div id="spmbulletcont-b1" class="spmbulletcont"></div>

B.1.1 Compared to 1850–1900, global surface temperature averaged over 2081–2100 is ''very likely'' to be higher by 1.0°C to 1.8°C under the very low GHG emissions scenario considered (SSP1-1.9), by 2.1°C to 3.5°C in the intermediate GHG emissions scenario (SSP2-4.5) and by 3.3°C to 5.7°C under the very high GHG emissions scenario (SSP5-8.5). <sup>[[#footnote-025|24]]</sup> The last time global surface temperature was sustained at or above 2.5°C higher than 1850–1900 was over 3 million years ago ( ''medium confidence'' ).   [[#table-spm-1|Table SPM.1]] Links to chapters 2.3, Cross-Chapter Box 2.4, 4.3, 4.5, Box TS.2, Box TS.4, Cross-Section Box TS.1

<div id="table-spm-1" class="Body-copy_Figures--tables-etc_•-Figure-title--bold-to-------spans-columns ParaOverride-2"></div>

'''Table SPM.1 | Changes in global surface temperature, which are assessed based on multiple lines of evidence, for selected 20-year time periods and the five illustrative emissions scenarios considered.''' Temperature differences relative to the average global surface temperature of the period 1850–1900 are reported in °C. This includes the revised assessment of observed historical warming for the AR5 reference period 1986–2005, which in AR6 is higher by 0.08 [–0.01 to +0.12] °C than in AR5 (see footnote 10). Changes relative to the recent reference period 1995–2014 may be calculated approximately by subtracting 0.85°C, the best estimate of the observed warming from 1850–1900 to 1995–2014.   Links to chapters Cross-Chapter Box 2.3, 4.3, 4.4, Cross-Section Box TS.1

[[File:86093ddfd668bba8d8095b6fca48328a IPCC_AR6_WGI_SPM_Table_1.png]]
B.1.2 Based on the assessment of multiple lines of evidence, global warming of 2°C, relative to 1850–1900, would be exceeded during the 21st century under the high and very high GHG emissions scenarios considered in this report (SSP3-7.0 and SSP5-8.5, respectively). Global warming of 2°C would ''extremely likely'' be exceeded in the intermediate GHG emissions scenario (SSP2-4.5). Under the very low and low GHG emissions scenarios, global warming of 2°C is ''extremely unlikely'' to be exceeded (SSP1-1.9) or ''unlikely'' to be exceeded (SSP1-2.6). <sup>[[#footnote-024|25]]</sup> Crossing the 2°C global warming level in the mid-term period (2041–2060) is ''very likely'' to occur under the very high GHG emissions scenario (SSP5-8.5), ''likely'' to occur under the high GHG emissions scenario (SSP3-7.0), and ''more likely than not'' to occur in the intermediate GHG emissions scenario (SSP2-4.5). <sup>[[#footnote-023|26]]</sup>   [[#table-spm-1|Table SPM.1]] [[#box-spm-1|Box SPM.1]] Links to chapters 4.3, Cross-Section Box TS.1

B.1.3 Global warming of 1.5°C relative to 1850–1900 would be exceeded during the 21st century under the intermediate, high and very high GHG emissions scenarios considered in this report (SSP2-4.5, SSP3-7.0 and SSP5-8.5, respectively). Under the five illustrative scenarios, in the near term (2021–2040), the 1.5°C global warming level is ''very likely'' to be exceeded under the very high GHG emissions scenario (SSP5-8.5), ''likely'' to be exceeded under the intermediate and high GHG emissions scenarios (SSP2-4.5 and SSP3-7.0), ''more likely than not'' to be exceeded under the low GHG emissions scenario (SSP1-2.6) and ''more likely than not'' to be reached under the very low GHG emissions scenario (SSP1-1.9). <sup>[[#footnote-022|27]]</sup> Furthermore, for the very low GHG emissions scenario (SSP1-1.9), it is ''more likely than not'' that global surface temperature would decline back to below 1.5°C toward the end of the 21st century, with a temporary overshoot of no more than 0.1°C above 1.5°C global warming.   [[#table-spm-1|]] [[#box-spm-1|Box SPM.1]] [[#figure-spm-4|Figure SPM.4]] Links to chapters 4.3, Cross-Section Box TS.1

B.1.4 Global surface temperature in any single year can vary above or below the long-term human-induced trend, due to substantial natural variability. <sup>[[#footnote-021|28]]</sup> The occurrence of individual years with global surface temperature change above a certain level, for example 1.5°C or 2°C, relative to 1850–1900 does not imply that this global warming level has been reached. <sup>[[#footnote-020|29]]</sup>   [[#table-spm-1|Table SPM.1]] [[#figure-spm-1|Figure SPM.1]] , [[#figure-spm-8|Figure SPM.8]] Links to chapters Cross-Chapter Box 2.3, 4.3, 4.4, Box 4.1, Cross-Section Box TS.1

'''B.2 Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, heavy precipitation, and, in some regions, agricultural and ecological droughts; an increase in the proportion of intense tropical cyclones; and reductions in Arctic sea ice, snow cover and permafrost.   Expand [[#figure-spm-5|Figures SPM.5]] , [[#figure-spm-6|SPM.6]] , [[#figure-spm-8|SPM.8]] Links to chapters 4.3, 4.5, 4.6, 7.4, 8.2, 8.4, Box 8.2, 9.3, 9.5, Box 9.2, 11.1, 11.2, 11.3, 11.4, 11.6, 11.7, 11.9, Cross-Chapter Box 11.1, 12.4, 12.5, Cross-Chapter Box 12.1, Atlas.4, Atlas.5, Atlas.6, Atlas.7, Atlas.8, Atlas.9, Atlas.10, Atlas.11'''
<div id="spmbulletcont-b2" class="spmbulletcont"></div>

B.2.1 It is ''virtually certain'' that the land surface will continue to warm more than the ocean surface ( ''likely'' 1.4 to 1.7 times more). It is ''virtually certain'' that the Arctic will continue to warm more than global surface temperature, with ''high confidence'' above two times the rate of global warming.   Links to chapters 2.3, 4.3, 4.5, 4.6, 7.4, 11.1, 11.3, 11.9, 12.4, 12.5, Cross-Chapter Box 12.1, Atlas.4, Atlas.5, Atlas.6, Atlas.7, Atlas.8, Atlas.9, Atlas.10, Atlas.11, Cross-Section Box TS.1, TS.2.6 [[#figure-spm-5|Figure SPM.5]]

B.2.2 With every additional increment of global warming, changes in extremes continue to become larger. For example, every additional 0.5°C of global warming causes clearly discernible increases in the intensity and frequency of hot extremes, including heatwaves ( ''very likely'' ) , and heavy precipitation ( ''high confidence'' ), as well as agricultural and ecological droughts <sup>[[#footnote-019|30]]</sup> in some regions ( ''high confidence'' ). Discernible changes in intensity and frequency of meteorological droughts, with more regions showing increases than decreases, are seen in some regions for every additional 0.5°C of global warming ( ''medium confidence'' ). Increases in frequency and intensity of hydrological droughts become larger with increasing global warming in some regions ( ''medium confidence'' ). There will be an increasing occurrence of some extreme events unprecedented in the observational record with additional global warming, even at 1.5°C of global warming. Projected percentage changes in frequency are larger for rarer events ( ''high confidence'' ).   Links to chapters 8.2, 11.2, 11.3, 11.4, 11.6, 11.9, Cross-Chapter Box 11.1, Cross-Chapter Box 12.1, TS.2.6 [[#figure-spm-5|Figure SPM.5]] [[#figure-spm-6|Figure SPM.6]]

B.2.3 Some mid-latitude and semi-arid regions, and the South American Monsoon region, are projected to see the highest increase in the temperature of the hottest days, at about 1.5 to 2 times the rate of global warming ( ''high confidence'' ). The Arctic is projected to experience the highest increase in the temperature of the coldest days, at about three times the rate of global warming ( ''high confidence'' ). With additional global warming, the frequency of marine heatwaves will continue to increase ( ''high confidence'' ), particularly in the tropical ocean and the Arctic ( ''medium confidence'' ).   Links to chapters Box 9.2, 11.1, 11.3, 11.9, Cross-Chapter Box 11.1, Cross-Chapter Box 12.1, 12.4, TS.2.4, TS.2.6 [[#figure-spm-6|Figure SPM.6]]

B.2.4 It is ''very likely'' that heavy precipitation events will intensify and become more frequent in most regions with additional global warming. At the global scale, extreme daily precipitation events are projected to intensify by about 7% for each 1°C of global warming ( ''high confidence'' ). The proportion of intense tropical cyclones (Category 4–5) and peak wind speeds of the most intense tropical cyclones are projected to increase at the global scale with increasing global warming ( ''high confidence'' ).   Links to chapters 8.2, 11.4, 11.7, 11.9, Cross-Chapter Box 11.1, Box TS.6, TS.4.3.1 [[#figure-spm-5|Figure SPM.5]] [[#figure-spm-6|Figure SPM.6]]

B.2.5 Additional warming is projected to further amplify permafrost thawing and loss of seasonal snow cover, of land ice and of Arctic sea ice ( ''high confidence'' ). The Arctic is ''likely'' to be practically sea ice-free in September <sup>[[#footnote-018|31]]</sup> at least once before 2050 under the five illustrative scenarios considered in this report, with more frequent occurrences for higher warming levels. There is ''low confidence'' in the projected decrease of Antarctic sea ice.   Links to chapters 4.3, 4.5, 7.4, 8.2, 8.4, Box 8.2, 9.3, 9.5, 12.4, Cross-Chapter Box 12.1, Atlas.5, Atlas.6, Atlas.8, Atlas.9, Atlas.11, TS.2.5 [[#figure-spm-8|Figure SPM.8]]

[[File:2a9e605bb01a664471f79745cb6f5452 IPCC_AR6_WGI_SPM_Figure_5_1.png]]
<div id="figure-spm-5" class="_idGenObjectLayout-1 Body-copy_Boxes_Blue-Boxes_•-Box-extract"></div>

[[File:e4383c7d4337935ae2d2eb08f913b27b IPCC_AR6_WGI_SPM_Figure_5_2.png]]

'''Figure SPM.5 | Changes in annual mean surface temperature, precipitation, and soil moisture'''

'''Panel (a) Comparison of observed and simulated annual mean surface temperature change.''' The '''left map''' shows the observed changes in annual mean surface temperature in the period 1850–2020 per °C of global warming (°C). The local (i.e., grid point) observed annual mean surface temperature changes are linearly regressed against the global surface temperature in the period 1850–2020. Observed temperature data are from Berkeley Earth, the dataset with the largest coverage and highest horizontal resolution. Linear regression is applied to all years for which data at the corresponding grid point is available. The regression method was used to take into account the complete observational time series and thereby reduce the role of internal variability at the grid point level. White indicates areas where time coverage was 100 years or less and thereby too short to calculate a reliable linear regression. The '''right map''' is based on model simulations and shows change in annual multi-model mean simulated temperatures at a global warming level of 1°C (20-year mean global surface temperature change relative to 1850–1900). The triangles at each end of the colour bar indicate out-of-bound values, that is, values above or below the given limits.

'''Panel (b) Simulated annual mean temperature change (°C), panel (c) precipitation change (%), and panel (d) total column soil moisture change (standard deviation of interannual variability)''' at global warming levels of 1.5°C, 2°C and 4°C (20-year mean global surface temperature change relative to 1850–1900). Simulated changes correspond to Coupled Model Intercomparison Project Phase 6 (CMIP6) multi-model mean change (median change for soil moisture) at the corresponding global warming level, that is, the same method as for the right map in panel (a).

In '''panel (c)''' , high positive percentage changes in dry regions may correspond to small absolute changes. In '''panel (d)''' , the unit is the standard deviation of interannual variability in soil moisture during 1850–1900. Standard deviation is a widely used metric in characterizing 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. In panel (d), large changes in dry regions with little interannual variability in the baseline conditions can correspond to small absolute change. The triangles at each end of the colour bars indicate out-of-bound values, that is, values above or below the given limits. Results from all models reaching the corresponding warming level in any of the five illustrative scenarios (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5) are averaged. Maps of annual mean temperature and precipitation changes at a global warming level of 3°C are available in Figure 4.31 and Figure 4.32 in [[IPCC:Wg1:Chapter:Chapter-4#4.6|Section 4.6]] ''.'' Corresponding maps of panels (b), (c) and (d), including hatching to indicate the level of model agreement at grid-cell level, are found in Figures 4.31, 4.32 and 11.19, respectively; as highlighted in Cross-Chapter Box Atlas.1, grid-cell level hatching is not informative for larger spatial scales (e.g., over AR6 reference regions) where the aggregated signals are less affected by small-scale variability, leading to an increase in robustness.   Links to chapters Figure 1.14, 4.6.1, Cross-Chapter Box 11.1, Cross-Chapter Box Atlas.1, TS.1.3.2, Figures TS.3 and TS.5

<div id="figure-spm-6" class="_idGenObjectLayout-1 Body-copy_Boxes_Blue-Boxes_•-Box-extract"></div>

<div id="_idContainer009" class="•-2-column-graphic"></div>

[[File:89f10c587d7c2c74085022b458b414ba IPCC_AR6_WGI_SPM_Figure_6.png]]

'''Figure SPM.6 | Projected changes in the intensity and frequency of hot temperature extremes over land, extreme precipitation over land, and agricultural and ecological droughts in drying regions'''

Projected changes are shown at global warming levels of 1°C, 1.5°C, 2°C, and 4°C and are relative to 1850–1900, <sup>[[#footnote-040|9]]</sup> representing a climate without human influence. The figure depicts frequencies and increases in intensity of 10- or 50-year extreme events from the base period (1850–1900) under different global warming levels.

'''Hot temperature extremes''' are defined as the daily maximum temperatures over land that were exceeded on average once in a decade (10-year event) or once in 50 years (50-year event) during the 1850–1900 reference period. '''Extreme precipitation events''' are defined as the daily precipitation amount over land that was exceeded on average once in a decade during the 1850–1900 reference period. '''Agricultural and ecological drought events''' are defined as the annual average of total column soil moisture below the 10th percentile of the 1850–1900 base period. These extremes are defined on model grid box scale. For hot temperature extremes and extreme precipitation, results are shown for the global land. For agricultural and ecological drought, results are shown for drying regions only, which correspond to the AR6 regions in which there is at least ''medium confidence'' in a projected increase in agricultural and ecological droughts at the 2°C warming level compared to the 1850–1900 base period in the Coupled Model Intercomparison Project Phase 6 (CMIP6). These regions include Western North America, Central North America, Northern Central America, Southern Central America, Caribbean, Northern South America, North-Eastern South America, South American Monsoon, South-Western South America, Southern South America, Western and Central Europe, Mediterranean, West Southern Africa, East Southern Africa, Madagascar, Eastern Australia, and Southern Australia (Caribbean is not included in the calculation of the figure because of the too-small number of full land grid cells). The non-drying regions do not show an overall increase or decrease in drought severity. Projections of changes in agricultural and ecological droughts in the CMIP Phase 5 (CMIP5) multi-model ensemble differ from those in CMIP6 in some regions, including in parts of Africa and Asia. Assessments of projected changes in meteorological and hydrological droughts are provided in Chapter 11.

In the '''‘frequency’ section''' , each year is represented by a dot. The dark dots indicate years in which the extreme threshold is exceeded, while light dots are years when the threshold is not exceeded. Values correspond to the medians (in bold) and their respective 5–95% range based on the multi-model ensemble from simulations of CMIP6 under different Shared Socio-economic Pathway scenarios. For consistency, the number of dark dots is based on the rounded-up median. In The '''‘intensity’ section''' , medians and their 5–95% range, also based on the multi-model ensemble from simulations of CMIP6, are displayed as dark and light bars, respectively. Changes in the intensity of hot temperature extremes and extreme precipitation are expressed as degree Celsius and percentage. As for agricultural and ecological drought, intensity changes are expressed as fractions of standard deviation of annual soil moisture.   Links to chapters 11.1; 11.3; 11.4; 11.6; 11.9; Figures 11.12, 11.15, 11.6, 11.7, and 11.18

'''B.3 Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events.   Expand [[#figure-spm-5|Figures SPM.5]] , [[#figure-spm-6|SPM.6]] Links to chapters 4.3, 4.4, 4.5, 4.6, 8.2, 8.3, 8.4, 8.5, Box 8.2, 11.4, 11.6, 11.9, 12.4, Atlas.3'''
<div id="spmbulletcont-b3" class="spmbulletcont"></div>

B.3.1 There is strengthened evidence since AR5 that the global water cycle will continue to intensify as global temperatures rise ( ''high confidence'' ), with precipitation and surface water flows projected to become more variable over most land regions within seasons ( ''high confidence'' ) and from year to year ( ''medium confidence'' ). The average annual global land precipitation is projected to increase by 0–5% under the very low GHG emissions scenario (SSP1-1.9), 1.5–8% for the intermediate GHG emissions scenario (SSP2-4.5) and 1–13% under the very high GHG emissions scenario (SSP5-8.5) by 2081–2100 relative to 1995–2014 ( ''likely'' ranges). Precipitation is projected to increase over high latitudes, the equatorial Pacific and parts of the monsoon regions, but decrease over parts of the subtropics and limited areas in the tropics in SSP2-4.5, SSP3-7.0 and SSP5-8.5 ( ''very likely'' ) . The portion of the global land experiencing detectable increases or decreases in seasonal mean precipitation is projected to increase ( ''medium confidence'' ). There is ''high confidence'' in an earlier onset of spring snowmelt, with higher peak flows at the expense of summer flows in snow-dominated regions globally.   [[#figure-spm-5|Figure SPM.5]] Links to chapters 4.3, 4.5, 4.6, 8.2, 8.4, Atlas.3, TS.2.6, TS.4.3, Box TS.6

B.3.2 A warmer climate will intensify very wet and very dry weather and climate events and seasons, with implications for flooding or drought ( ''high confidence'' ), but the location and frequency of these events depend on projected changes in regional atmospheric circulation, including monsoons and mid-latitude storm tracks. It is ''very likely'' that rainfall variability related to the El Niño–Southern Oscillation is projected to be amplified by the second half of the 21st century in the SSP2-4.5, SSP3-7.0 and SSP5-8.5 scenarios.   [[#figure-spm-5|Figure SPM.5]] [[#figure-spm-6|Figure SPM.6]] Links to chapters 4.3, 4.5, 4.6, 8.2, 8.4, 8.5, 11.4, 11.6, 11.9, 12.4, TS.2.6, TS.4.2, Box TS.6

B.3.3 Monsoon precipitation is projected to increase in the mid- to long term at the global scale, particularly over South and South East Asia, East Asia and West Africa apart from the far west Sahel ( ''high confidence'' ). The monsoon season is projected to have a delayed onset over North and South America and West Africa ( ''high confidence'' ) and a delayed retreat over West Africa ( ''medium confidence'' ).   Links to chapters 4.4, 4.5, 8.2, 8.3, 8.4, Box 8.2, Box TS.13

B.3.4 A projected southward shift and intensification of Southern Hemisphere summer mid-latitude storm tracks and associated precipitation is ''likely'' in the long term under high GHG emissions scenarios (SSP3-7.0, SSP5-8.5), but in the near term the effect of stratospheric ozone recovery counteracts these changes ( ''high confidence'' ). There is ''medium confidence'' in a continued poleward shift of storms and their precipitation in the North Pacific, while there is ''low confidence'' in projected changes in the North Atlantic storm tracks.   Links to chapters 4.4, 4.5, 8.4, TS.2.3, TS.4.2

'''B.4 Under scenarios with increasing CO <sub>2</sub> emissions, the ocean and land carbon sinks are projected to be less effective at slowing the accumulation of CO <sub>2</sub> in the atmosphere.   Expand [[#figure-spm-7|Figure SPM.7]] Links to chapters 4.3, 5.2, 5.4, 5.5, 5.6'''
<div id="spmbulletcont-b4" class="spmbulletcont"></div>

B.4.1 While natural land and ocean carbon sinks are projected to take up, in absolute terms, a progressively larger amount of CO <sub>2</sub> under higher compared to lower CO <sub>2</sub> emissions scenarios, they become less effective, that is, the proportion of emissions taken up by land and ocean decrease with increasing cumulative CO <sub>2</sub> emissions. This is projected to result in a higher proportion of emitted CO <sub>2</sub> remaining in the atmosphere ( ''high confidence'' ).   [[#figure-spm-7|Figure SPM.7]] Links to chapters 5.2, 5.4, Box TS.5

B.4.2 Based on model projections, under the intermediate GHG emissions scenario that stabilizes atmospheric CO <sub>2</sub> concentrations this century (SSP2-4.5), the rates of CO <sub>2</sub> taken up by the land and ocean are projected to decrease in the second half of the 21st century ( ''high confidence'' ). Under the very low and low GHG emissions scenarios (SSP1-1.9, SSP1-2.6), where CO <sub>2</sub> concentrations peak and decline during the 21st century, the land and ocean begin to take up less carbon in response to declining atmospheric CO <sub>2</sub> concentrations ( ''high confidence'' ) and turn into a weak net source by 2100 under SSP1-1.9 ( ''medium confidence'' ). It is ''very unlikely'' that the combined global land and ocean sink will turn into a source by 2100 under scenarios without net negative emissions (SSP2-4.5, SSP3-7.0, SSP5-8.5). <sup>[[#footnote-017|32]]</sup>   Links to chapters 4.3, 5.4, 5.5, 5.6, Box TS.5, TS.3.3

B.4.3 The magnitude of feedbacks between climate change and the carbon cycle becomes larger but also more uncertain in high CO <sub>2</sub> emissions scenarios ( ''very high confidence'' ). However, climate model projections show that the uncertainties in atmospheric CO <sub>2</sub> concentrations by 2100 are dominated by the differences between emissions scenarios ( ''high confidence'' ). Additional ecosystem responses to warming not yet fully included in climate models, such as CO <sub>2</sub> and CH <sub>4</sub> fluxes from wetlands, permafrost thaw and wildfires, would further increase concentrations of these gases in the atmosphere ( ''high confidence'' ).   Links to chapters 5.4, Box TS.5, TS.3.2

<div id="figure-spm-7" class="_idGenObjectLayout-1 Body-copy_Boxes_Blue-Boxes_•-Box-extract"></div>

<div id="_idContainer010" class="•-2-column-graphic"></div>

[[File:849eca1baf7738bf4a20e5e54a9e8163 IPCC_AR6_WGI_SPM_Figure_7.png]]

Figure SPM.7 | Cumulative anthropogenic CO <sub>2</sub> emissions taken up by land and ocean sinks by 2100 under the five illustrative scenarios

The cumulative anthropogenic (human-caused) carbon dioxide (CO <sub>2</sub> ) emissions taken up by the land and ocean sinks under the five illustrative scenarios (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5) are simulated from 1850 to 2100 by Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models in the concentration-driven simulations. Land and ocean carbon sinks respond to past, current and future emissions; therefore, cumulative sinks from 1850 to 2100 are presented here. During the historical period (1850–2019) the observed land and ocean sink took up 1430 GtCO <sub>2</sub> (59% of the emissions).

'''The bar chart''' illustrates the projected amount of cumulative anthropogenic CO <sub>2</sub> emissions (GtCO <sub>2</sub> ) between 1850 and 2100 remaining in the atmosphere (grey part) and taken up by the land and ocean (coloured part) in the year 2100. '''The doughnut chart''' illustrates the proportion of the cumulative anthropogenic CO <sub>2</sub> emissions taken up by the land and ocean sinks and remaining in the atmosphere in the year 2100. Values in % indicate the proportion of the cumulative anthropogenic CO <sub>2</sub> emissions taken up by the combined land and ocean sinks in the year 2100. The overall anthropogenic carbon emissions are calculated by adding the net global land-use emissions from the CMIP6 scenario database to the other sectoral emissions calculated from climate model runs with prescribed CO <sub>2</sub> concentrations. <sup>[[#footnote-016|33]]</sup> Land and ocean CO <sub>2</sub> uptake since 1850 is calculated from the net biome productivity on land, corrected for CO <sub>2</sub> losses due to land-use change by adding the land-use change emissions, and net ocean CO <sub>2</sub> flux.   Links to chapters 5.2.1; Table 5.1; 5.4.5; Figure 5.25; Box TS.5; Box TS.5, Figure 1

'''B.5 Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level.   Expand [[#figure-spm-8|Figure SPM.8]] Links to chapters 2.3, Cross-Chapter Box 2.4, 4.3, 4.5, 4.7, 5.3, 9.2, 9.4, 9.5, 9.6, Box 9.4'''
<div id="spmbulletcont-b5" class="spmbulletcont"></div>

B.5.1 Past GHG emissions since 1750 have committed the global ocean to future warming ( ''high confidence'' ). Over the rest of the 21st century, ''likely'' ocean warming ranges from 2–4 (SSP1-2.6) to 4–8 times (SSP5-8.5) the 1971–2018 change. Based on multiple lines of evidence, upper ocean stratification ( ''virtually certain'' ), ocean acidification ( ''virtually certain'' ) and ocean deoxygenation ( ''high confidence'' ) will continue to increase in the 21st century, at rates dependent on future emissions. Changes are irreversible on centennial to millennial time scales in global ocean temperature ( ''very high confidence'' ), deep-ocean acidification ( ''very high confidence'' ) and deoxygenation ( ''medium confidence'' ).   [[#figure-spm-8|Figure SPM.8]] Links to chapters 4.3, 4.5, 4.7, 5.3, 9.2, TS.2.4

B.5.2 Mountain and polar glaciers are committed to continue melting for decades or centuries ( ''very high confidence'' ). Loss of permafrost carbon following permafrost thaw is irreversible at centennial time scales ( ''high confidence'' ). Continued ice loss over the 21st century is ''virtually certain'' for the Greenland Ice Sheet and ''likely'' for the Antarctic Ice Sheet. There is ''high confidence'' that total ice loss from the Greenland Ice Sheet will increase with cumulative emissions. There is ''limited evidence'' for low-likelihood, high-impact outcomes (resulting from ice-sheet instability processes characterized by deep uncertainty and in some cases involving tipping points) that would strongly increase ice loss from the Antarctic Ice Sheet for centuries under high GHG emissions scenarios. <sup>[[#footnote-015|34]]</sup>   Links to chapters 4.3, 4.7, 5.4, 9.4, 9.5, Box 9.4, Box TS.1, TS.2.5

B.5.3 It is ''virtually certain'' that global mean sea level will continue to rise over the 21st century. Relative to 1995–2014, the ''likely'' global mean sea level rise by 2100 is 0.28–0.55 m under the very low GHG emissions scenario (SSP1-1.9); 0.32–0.62 m under the low GHG emissions scenario (SSP1-2.6); 0.44–0.76 m under the intermediate GHG emissions scenario (SSP2-4.5); and 0.63–1.01 m under the very high GHG emissions scenario (SSP5-8.5); and by 2150 is 0.37–0.86 m under the very low scenario (SSP1-1.9); 0.46–0.99 m under the low scenario (SSP1-2.6); 0.66–1.33 m under the intermediate scenario (SSP2-4.5); and 0.98–1.88 m under the very high scenario (SSP5-8.5) ( ''medium confidence'' ). <sup>[[#footnote-014|35]]</sup> Global mean sea level rise above the ''likely'' range – approaching 2 m by 2100 and 5 m by 2150 under a very high GHG emissions scenario (SSP5-8.5) ( ''low confidence'' ) – cannot be ruled out due to deep uncertainty in ice-sheet processes.   [[#figure-spm-8|Figure SPM.8]] Links to chapters 4.3, 9.6, Box 9.4, Box TS.4

B.5.4 In the longer term, sea level is committed to rise for centuries to millennia due to continuing deep-ocean warming and ice-sheet melt and will remain elevated for thousands of years ( ''high confidence'' ). Over the next 2000 years, global mean sea level will rise by about 2 to 3 m if warming is limited to 1.5°C, 2 to 6 m if limited to 2°C and 19 to 22 m with 5°C of warming, and it will continue to rise over subsequent millennia ( ''low confidence'' ). Projections of multi-millennial global mean sea level rise are consistent with reconstructed levels during past warm climate periods: ''likely'' 5–10 m higher than today around 125,000 years ago, when global temperatures were ''very likely'' 0.5°C–1.5°C higher than 1850–1900; and ''very likely'' 5–25 m higher roughly 3 million years ago, when global temperatures were 2.5°C–4°C higher ( ''medium confidence'' ).   Links to chapters 2.3, Cross-Chapter Box 2.4, 9.6, Box TS.2, Box TS.4, Box TS.9

<div id="figure-spm-8" class="_idGenObjectLayout-1 Body-copy_Boxes_Blue-Boxes_•-Box-extract"></div>

<div id="_idContainer011" class="•-2-column-graphic"></div>

[[File:7105c442e0d4d5718c43c0c3f2b0ed63 IPCC_AR6_WGI_SPM_Figure_8.png]]

Figure SPM.8 | Selected indicators of global climate change under the five illustrative scenarios used in this Report

The projections for each of the five scenarios are shown in colour. Shades represent uncertainty ranges – more detail is provided for each panel below. The black curves represent the historical simulations (panels a, b, c) or the observations (panel d). Historical values are included in all graphs to provide context for the projected future changes.

'''Panel (a) Global surface temperature changes''' in °C relative to 1850–1900. These changes were obtained by combining Coupled Model Intercomparison Project Phase 6 (CMIP6) model simulations with observational constraints based on past simulated warming, as well as an updated assessment of equilibrium climate sensitivity (see Box SPM.1). Changes relative to 1850–1900 based on 20-year averaging periods are calculated by adding 0.85°C (the observed global surface temperature increase from 1850–1900 to 1995–2014) to simulated changes relative to 1995–2014. ''Very likely'' ranges are shown for SSP1-2.6 and SSP3-7.0.

'''Panel (b) September Arctic sea ice area''' in 10 <sup>6</sup> km <sup>2</sup> based on CMIP6 model simulations. ''Very likely'' ranges are shown for SSP1-2.6 and SSP3-7.0. The Arctic is projected to be practically ice-free near mid-century under intermediate and high GHG emissions scenarios.

'''Panel (c) Global ocean surface pH''' (a measure of acidity) based on CMIP6 model simulations. ''Very likely'' ranges are shown for SSP1-2.6 and SSP3-7.0.

'''Panel (d) Global mean sea level change''' in metres, relative to 1900. The historical changes are observed (from tide gauges before 1992 and altimeters afterwards), and the future changes are assessed consistently with observational constraints based on emulation of CMIP, ice-sheet, and glacier models. ''Likely'' ranges are shown for SSP1-2.6 and SSP3-7.0. Only ''likely'' ranges are assessed for sea level changes due to difficulties in estimating the distribution of deeply uncertain processes. The dashed curve indicates the potential impact of these deeply uncertain processes. It shows the 83rd percentile of SSP5-8.5 projections that include low-likelihood, high-impact ice-sheet processes that cannot be ruled out; because of ''low confidence'' in projections of these processes, this curve does not constitute part of a ''likely'' range. Changes relative to 1900 are calculated by adding 0.158 m (observed global mean sea level rise from 1900 to 1995–2014) to simulated and observed changes relative to 1995–2014.

'''Panel (e) Global mean sea level change at 2300''' in metres relative to 1900. Only SSP1-2.6 and SSP5-8.5 are projected at 2300, as simulations that extend beyond 2100 for the other scenarios are too few for robust results. The 17th–83rd percentile ranges are shaded. The dashed arrow illustrates the 83rd percentile of SSP5-8.5 projections that include low-likelihood, high-impact ice-sheet processes that cannot be ruled out.

Panels (b) and (c) are based on single simulations from each model, and so include a component of internal variability. Panels (a), (d) and (e) are based on long-term averages, and hence the contributions from internal variability are small.   Links to chapters 4.3; Figures 4.2, 4.8, 4.11; 9.6; Figure 9.27; Figures TS.8 and TS.11; Box TS.4 Figure 1

<div id="C." class="h1-container"></div>

<span id="c.-climate-information-for-risk-assessment-and-regional-adaptation"></span>