Editing IPCC:AR6/WGI/Chapter-1 (section)

== Appendix 1.A. Historical Overview of Major Conclusions of IPCC Assessment Reports ==

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'''Table 1.A.1''' | '''Historical overview of major conclusions of IPCC assessment reports.''' The table repeats Table 1.1 from the IPCC Fifth Assessment Report (AR5; [[#Cubasch--2013|Cubasch et al., 2013]] ) and extends it with the AR5 and AR6 key findings. The table provides a non-comprehensive selection of key Summary for Policymakers (SPM) statements from previous assessment reports – IPCC First Assessment Report (FAR; [[#IPCC--1990b|IPCC, 1990b]] ), IPCC Second Assessment Report (SAR; [[#IPCC--1995b|IPCC, 1995b]] ), IPCC Third Assessment Report (TAR; [[#IPCC--2001b|IPCC, 2001b]] ), IPCC Fourth Assessment Report (AR4; [[#IPCC--2007b|IPCC, 2007b]] ), IPCC Fifth Assessment Report (AR5; [[#IPCC--2013b|IPCC, 2013b]] ), and the IPCC Sixth Assessment Report (AR6; IPCC, 2021) – with a focus on global mean surface air temperature and sea level change as two policy-relevant quantities that have been covered in IPCC since the FAR.

{| class="wikitable"
|-
! '''Topic'''

! '''FAR SPM Statement (1990)'''

! '''SAR SPM Statement (1995)'''

! '''TAR SPM Statement (2001)'''

! '''AR4 SPM Statement (2007)'''

! '''AR5 SPM statement (2013)'''

! '''AR6 SPM statement (2021)'''

|-
| rowspan="3"| '''Human and Natural Drivers of Climate Change'''

| There is a natural greenhouse effect, which already keeps the Earth warmer than it would otherwise be. Emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases carbon dioxide, methane, chlorofluorocarbons and nitrous oxide. These increases will enhance the greenhouse effect, resulting on average in an additional warming of the Earth’s surface.

| Greenhouse gas concentrations have continued to increase. These trends can be attributed largely to human activities, mostly fossil fuel use, land use change and agriculture.

| Emissions of greenhouse gases and aerosols due to human activities continue to alter the atmosphere in ways that are expected to affect the climate. The atmospheric concentration of CO <sub>2</sub> has increased by 31% since 1750 and that of methane by 151%.

| Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land use change, while those of methane and nitrous oxide are primarily due to agriculture.

| Total radiative forcing is positive, and has led to an uptake of energy by the climate system. The largest contribution to total radiative forcing is caused by the increase in the atmospheric concentration of CO <sub>2</sub> since 1750.

| Observed increases in well-mixed greenhouse gas (GHG) concentrations since around 1750 are unequivocally caused by human activities. Since 2011 (measurements reported in AR5), concentrations have continued to increase in the atmosphere, reaching annual averages of 410 parts per million (ppm) for carbon dioxide (CO <sub>2</sub> ), 1866 parts per billion (ppb) for methane (CH <sub>4</sub> ), and 332 ppb for nitrous oxide (N <sub>2</sub> O) in 2019.

|-
| Continued emissions of these gases at present rates would commit us to increased concentrations for centuries ahead.

| Anthropogenic aerosols are short-lived and tend to produce negative radiative forcing.

| Anthropogenic aerosols are short-lived and mostly produce negative radiative forcing by their direct effect. There is more evidence for their indirect effect, which is negative, although of very uncertain magnitude.

| ''Very high confidence'' that the global average net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 [+0.6 to +2.4] W m <sup>–2</sup> .

| The total anthropogenic radiative forcing (RF) for 2011 relative to 1750 is 2.29 [1.13 to 3.33] W m <sup>−2</sup> ), and it has increased more rapidly since 1970 than during prior decades. The total anthropogenic RF best estimate for 2011 is 43% higher than that reported in AR4 for the year 2005.

| Human-caused radiative forcing of 2.72 [1.96 to 3.48] W m–2 in 2019 relative to 1750 has warmed the climate system. This warming is mainly due to increased GHG concentrations, partly reduced by cooling due to increased aerosol concentrations. The radiative forcing has increased by 0.43 W m <sup>–2</sup> (19%) relative to AR5, of which 0.34 W m <sup>–2</sup> is due to the increase in GHG concentrations since 2011. The remainder is due to improved scientific understanding and changes in the assessment of aerosol forcing, which include decreases in concentration and improvement in its calculation ( ''high confidence'' ).

|-
|
| Natural factors have made small contributions to radiative forcing over the past century.

|
| The total natural RF from solar irradiance changes and stratospheric volcanic aerosols made only a small contribution to the net radiative forcing throughout the last century, except for brief periods after large volcanic eruptions.

|
|-
| rowspan="3"| '''Observations of Recent Climate Change: Temperature'''

| rowspan="3"| Global mean surface air temperature has increased by 0.3°C to 0.6°C over the last 100 years, with the five global-average warmest years being in the 1980s.

| rowspan="3"| Climate has changed over the past century. Global mean surface temperature has increased by between about 0.3 and 0.6°C since the late 19th century. Recent years have been among the warmest since 1860, despite the cooling effect of the 1991 Mt. Pinatubo volcanic eruption.

| An increasing body of observations gives a collective picture of a warming world and other changes in the climate system.

| Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.

| Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.

| Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred.

|-
| The global average temperature has increased since 1861. Over the 20th century the increase has been 0.6°C.

| Eleven of the last twelve years (1995–2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850). The updated 100-year linear trend (1906 to 2005) of 0.74°C [0.56°C to 0.92°C] is therefore larger than the corresponding trend for 1901 to 2000 given in the TAR of 0.6°C [0.4°C to 0.8°C].

| Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850. The globally averaged combined land and ocean surface temperature data as calculated by a linear trend, show a warming of 0.85 [0.65 to 1.06] °C, over the period 1880 to 2012.

| Each of the last four decades has been successively warmer than any decade that preceded it since 1850. Global surface temperature8 in the first two decades of the 21st century (2001–2020) was 0.99 [0.84 to 1.10] °C higher than 1850–1900.9 Global surface temperature was 1.09 [0.95 to 1.20] °C higher in 2011–2020 than 1850–1900, with larger increases over land (1.59 [1.34 to 1.83] °C) than over the ocean (0.88 [0.68 to 1.01] °C).

|-
| Some important aspects of climate appear not to have changed.

| Some aspects of climate have not been observed to change.

|
|-
| '''Observations of Recent Climate Change: Sea Level'''

| Over the same period global sea level has increased by 10 to 20 cm. These increases have not been smooth with time nor uniform over the globe.

| Global sea level has risen by between 10 and 25 cm over the past 100 years and much of the rise may be related to the increase in global mean temperature.

| Tide gauge data show that global average sea level rose between 0.1 and 0.2 m during the 20th century.

| Global average sea level rose at an average rate of 1.8 [1.3 to 2.3] mm yr <sup>–1</sup> over 1961 to 2003. The rate was faster over 1993 to 2003: about 3.1 [2.4 to 3.8] mm yr <sup>–1</sup> . The total 20th century rise is estimated to be 0.17 [0.12 to 0.22] m.

| The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia ( ''high confidence'' ). Over the period 1901 to 2010, global mean sea level rose by 0.19 [0.17 to 0.21] m.

| Global mean sea level increased by 0.20 [0.15 to 0.25] m between 1901 and 2018. The average rate of sea level rise was 1.3 [0.6 to 2.1] mm yr <sup>–1</sup> between 1901 and 1971, increasing to 1.9 [0.8 to 2.9] mm yr <sup>–1</sup> between 1971 and 2006, and further increasing to 3.7 [3.2 to 4.2] mm yr <sup>–1</sup> between 2006 and 2018 ( ''high confidence'' ). Human influence was ''very likely'' the main driver of these increases since at least 1971.

|-
| '''Observations of Recent Climate Change: Ocean Heat Content'''

|
| Global ocean heat content has increased since the late1950s, the period for which adequate observations of sub-surface ocean temperatures have been available.

| Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000 m and that the ocean has been absorbing more than 80% of the heat added to the climate system. Such warming causes seawater to expand, contributing to sea level rise.

| Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 ( ''high confidence'' ). It is ''virtually certain'' that the upper ocean (0−700 m) warmed from 1971 to 2010, and it ''likely'' warmed between the 1870s and 1971. On a global scale, the ocean warming is largest near the surface, and the upper 75 m warmed by 0.11 [0.09 to 0.13] °C per decade over the period 1971 to 2010. Instrumental biases in upper-ocean temperature records have been identified and reduced, enhancing confidence in the assessment of change.

| Human-caused net positive radiative forcing causes an accumulation of additional energy (heating) in the climate system, partly reduced by increased energy loss to space in response to surface warming. The observed average rate of heating of the climate system increased from 0.50 [0.32 to 0.69] W m <sup>–2</sup> for the period 1971–2006 to 0.79 [0.52 to 1.06] W m <sup>–2</sup> for the period 2006–2018 ( ''high confidence'' ). Ocean warming accounted for 91% of the heating in the climate system, with land warming, ice loss and atmospheric warming accounting for about 5%, 3% and 1%, respectively ( ''high confidence'' ).

|-
| '''Observations of Recent Climate Change: Carbon Cycle/Ocean Acidification'''

|
| Increasing atmospheric carbon dioxide concentrations lead to increasing acidification of the ocean. Projections based on SRES scenarios give reductions in average global surface ocean pH of between 0.14 and 0.35 units over the 21st century, adding to the present decrease of 0.1 units since pre-industrial times.

| The atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have increased to levels unprecedented in at least the last 800,000 years. Carbon dioxide concentrations have increased by 40% since pre-industrial times, primarily from fossil fuel emissions and secondarily from net land use change emissions. The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification.

| In 2019, atmospheric CO <sub>2</sub> concentrations were higher than at any time in at least 2 million years ( ''high confidence'' ), and concentrations of CH <sub>4</sub> and N <sub>2</sub> O were higher than at any time in at least 800,000 years ( ''very high confidence'' ). Since 1750, increases in CO <sub>2</sub> (47%) and CH <sub>4</sub> (156%) concentrations far exceed – and increases in N <sub>2</sub> O (23%) are similar to – the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years ( ''very high confidence'' ).

|-
| rowspan="2"| '''A Paleoclimatic Perspective'''

| rowspan="2"| Climate varies naturally on all time scales from hundreds of millions of years down to the year-to-year. Prominent in the Earth’s history have been the 100,000-year glacial–interglacial cycles when climate was mostly cooler than at present. Global surface temperatures have typically varied by 5°C to 7°C through these cycles, with large changes in ice volume and sea level, and temperature changes as great as 10°C to 15°C in some middle and high latitude regions of the Northern Hemisphere. Since the end of the last ice age, about 10,000 years ago, global surface temperatures have probably fluctuated by little more than 1°C. Some fluctuations have lasted several centuries, including the period 1400–1900 which ended in the 19th century and which appears to have been global in extent.

| rowspan="2"| The limited available evidence from proxy climate indicators suggests that the 20th century global mean temperature is at least as warm as any other century since at least 1400 AD. Data prior to 1400 are too sparse to allow the reliable estimation of global mean temperature.

| rowspan="2"| New analyses of proxy data for the Northern Hemisphere indicate that the increase in temperature in the 20th century is ''likely'' to have been the largest of any century during the past 1,000 years. It is also ''likely'' that, in the Northern Hemisphere, the 1990s was the warmest decade and 1998 the warmest year. Because less data are available, less is known about annual averages prior to 1,000 years before present and for conditions prevailing in most of the Southern Hemisphere prior to 1861.

| Palaeoclimatic information supports the interpretation that the warmth of the last half-century is unusual in at least the previous 1,300 years.

| In the Northern Hemisphere, 1983–2012 was ''likely'' the warmest 30-year period of the last 1400 years ( ''medium confidence'' ).

| The scale of recent changes across the climate system as a whole – and the present state of many aspects of the climate system – are unprecedented over many centuries to many thousands of years. Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years ( ''high confidence'' ). Temperatures during the most recent decade (2011–2020) exceed those of the most recent multi-century warm period, around 6500 years ago [0.2°C to 1°C relative to 1850–1900] ( ''medium confidence'' ). Prior to that, the next most recent warm period was about 125,000 years ago, when the multi-century temperature [0.5°C to 1.5°C relative to 1850–1900] overlaps the observations of the most recent decade ( ''medium confidence'' ).

|-
| The last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6 m of sea level rise.

| There is ''very high confidence'' that maximum global mean sea level during the last interglacial period (129,000 to 116,000 years ago) was, for several thousand years, at least 5 m higher than present, and ''high confidence'' that it did not exceed 10 m above present.

| Global mean sea level has risen faster since 1900 than over any preceding century in at least the last 3000 years ( ''high confidence'' ). The global ocean has warmed faster over the past century than since the end of the last deglacial transition (around 11,000 years ago) ( ''medium confidence'' ). A long-term increase in surface open ocean pH occurred over the past 50 million years ( ''high confidence'' ). However, surface open ocean pH as low as recent decades is unusual in the last 2 million years ( ''medium confidence'' ).

|-
| '''Understanding and Attributing Climate Change'''

| The size of this warming is broadly consistent with predictions of climate models, but it is also of the same magnitude as natural climate variability. Thus, the observed increase could be largely due to this natural variability; alternatively, this variability and other human factors could have offset a still larger human-induced greenhouse warming. The unequivocal detection of the enhanced greenhouse effect from observations is ''not likely'' for a decade or more.

| The balance of evidence suggests a discernible human influence on global climate. Simulations with coupled atmosphere–ocean models have provided important information about decade to century time scale natural internal climate variability.

| There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities. There is a longer and more scrutinized temperature record and new model estimates of variability. Reconstructions of climate data for the past 1,000 years indicate this warming was unusual and is ''unlikely'' to be entirely natural in origin.

| Most of the observed increase in global average temperatures since the mid-20th century is ''very likely'' due to the observed increase in anthropogenic greenhouse gas concentrations. Discernible human influence now extends to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.

| Human influence on the climate system is clear. It is ''extremely likely'' that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic forcings together. The best estimate of the human-induced contribution to warming is similar to the observed warming over this period.

| It is unequivocal that human influence has warmed the atmosphere, ocean and land. The ''likely'' range of total human-caused global surface temperature increase from 1850–1900 to 2010–201911 is 0.8°C to 1.3°C, with a best estimate of 1.07°C. It is ''likely'' that well-mixed GHGs contributed a warming of 1.0°C to 2.0°C, other human drivers (principally aerosols) contributed a cooling of 0.0°C to 0.8°C, natural drivers changed global surface temperature by –0.1°C to +0.1°C, and internal variability changed it by –0.2°C to +0.2°C. It is ''very likely'' that well-mixed GHGs were the main driver12 of tropospheric warming since 1979 and ''extremely likely'' that human-caused stratospheric ozone depletion was the main driver of cooling of the lower stratosphere between 1979 and the mid-1990s.

|-
| rowspan="3"| '''Projections of Future Changes in Climate: Temperature'''

| rowspan="3"| Under the IPCC Business-as-Usual emissions of greenhouse gases, a rate of increase of global mean temperature during the next century of about 0.3°C per decade (with an uncertainty range of 0.2°C to 0.5°C per decade); this is greater than that seen over the past 10,000 years.

| rowspan="3"| Climate is expected to continue to change in the future. For the mid-range IPCC emissions scenario, IS92a, assuming the ‘best estimate’ value of climate sensitivity and including the effects of future increases in aerosols, models project an increase in global mean surface air temperature relative to 1990 of about 2°C by 2100.

| Global average temperature and sea level are projected to rise under all IPCC SRES scenarios. The globally averaged surface temperature is projected to increase by 1.4°C to 5.8°C over the period 1990 to 2100.

| For the next two decades, a warming of about 0.2°C per decade is projected for a range of SRES emissions scenarios. Even if the concentrations of all greenhouse gases and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected.

| Global surface temperature change for the end of the 21st century is ''likely'' to exceed 1.5°C relative to 1850 to 1900 for all RCP scenarios except RCP2.6. It is likely to exceed 2°C for RCP6.0 and RCP8.5, and ''more likely than not'' to exceed 2°C for RCP4.5. Warming will continue beyond 2100 under all RCP scenarios except RCP2.6. Warming will continue to exhibit interannual-to-decadal variability and will not be regionally uniform.

| 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).

|-
| Confidence in the ability of models to project future climate has increased.

| There is now higher confidence in projected patterns of warming and other regional-scale features, including changes in wind patterns, precipitation and some aspects of extremes and of ice.

| Climate models have improved since the AR4. Models reproduce observed continental-scale surface temperature patterns and trends over many decades, including the more rapid warming since the mid-20th century and the cooling immediately following large volcanic eruptions.

| 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.

|-
| Anthropogenic climate change will persist for many centuries.

| Anthropogenic warming and sea level rise would continue for centuries, even if greenhouse gas concentrations were to be stabilised.

| Cumulative emissions of CO <sub>2</sub> largely determine global mean surface warming by the late 21st century and beyond. Most aspects of climate change will persist for many centuries even if emissions of CO <sub>2</sub> are stopped. This represents a substantial multi-century climate change commitment created by past, present and future emissions of CO <sub>2</sub> .

| This Report reaffirms with ''high confidence'' the AR5 finding that there is a near-linear relationship between cumulative anthropogenic CO <sub>2</sub> emissions and the global warming they cause. Each 1000 GtCO <sub>2</sub> of cumulative CO <sub>2</sub> emissions is assessed to ''likely'' cause a 0.27°C to 0.63°C increase in global surface temperature with a best estimate of 0.45°C. This is a narrower range compared to AR5 and SR1.5. This quantity is referred to as the transient climate response to cumulative CO <sub>2</sub> emissions (TCRE). This relationship implies that reaching net zero anthropogenic CO <sub>2</sub> emissions is a requirement to stabilize human-induced global temperature increase at any level, but that limiting global temperature increase to a specific level would imply limiting cumulative CO <sub>2</sub> emissions to within a carbon budget.

|-
| '''Projections of Future Changes in Climate: Sea Level'''

| An average rate of global mean sea level rise of about 6 cm per decade over the next century (with an uncertainty range of 3 to 10 cm per decade) is projected.

| For the IS92a scenario, assuming the ‘best estimate’ values of climate

sensitivity and of ice melt sensitivity to warming and including the effects of future changes in aerosol concentrations, models project a sea level rise of about 50 cm from the present to 2100. The corresponding ‘low’ and ‘high’ projections are 15 and 95 cm.

| Global mean sea level is projected to rise by 0.09 to 0.88 m between 1990 and 2100.

| Global sea level rise for the range of scenarios is projected as 0.18 to 0.59 m by the end of the 21st century.

| Global mean sea level rise for 2081–2100 relative to 1986–2005 will ''likely'' be in the ranges of 0.26 to 0.55 m for RCP2.6, 0.32 to 0.63 m for RCP4.5, 0.33 to 0.63 m for RCP6.0, and 0.45 to 0.82 m for RCP8.5.

| 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'' ). 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.

|-
| '''Projections of Future Changes in Climate: AMOC'''

|
| Most simulations show a reduction in the strength of the North Atlantic thermohaline circulation. Future unexpected, large and rapid climate system changes are difficult to predict. These arise from the non-linear nature of the climate system. Examples include rapid circulation changes in the North Atlantic.

| Most models show weakening of the ocean thermohaline circulation, which leads to a reduction of the heat transport into high latitudes of the Northern Hemisphere. However, even in models where the thermohaline circulation weakens, there is still a warming over Europe due to increased greenhouse gases. The current projections using climate models do not exhibit a complete shut-down of the thermohaline circulation by 2100. Beyond 2100, the thermohaline circulation could completely, and possibly irreversibly, shut-down in either hemisphere if the change in radiative forcing is large enough and applied long enough.

| Based on current model simulations, it is ''very likely'' that the meridional overturning circulation (MOC) of the Atlantic Ocean will slow down during the 21st century. It is ''very unlikely'' that the MOC will undergo a large abrupt transition during the 21st century. Longer-term changes in the MOC cannot be assessed with confidence.

| It is ''very likely'' that the Atlantic Meridional Overturning Circulation (AMOC) will weaken over the 21st century. It is ''very unlikely'' that the AMOC will undergo an abrupt transition or collapse in the 21st century for the scenarios considered. There is ''low confidence'' in assessing the evolution of the AMOC beyond the 21st century because of the limited number of analyses and equivocal results. However, a collapse beyond the 21st century for large sustained warming cannot be excluded.

| The Atlantic Meridional Overturning Circulation is ''very likely'' to weaken over the 21st century for all emissions scenarios. While there is ''high confidence'' in the 21st century decline, there is only ''low confidence'' in the magnitude of the trend. There is ''medium confidence'' that there will not be an abrupt collapse before 2100. If such a collapse were to occur, it would ''very likely'' cause abrupt shifts in regional weather patterns and water cycle, such as a southward shift in the tropical rain belt, weakening of the African and Asian monsoons and strengthening of Southern Hemisphere monsoons, and drying in Europe.

|}

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<div id="footnote-007" class="_idFootnote"></div>

[[#footnote-007-backlink|1]] Note that GMST and GSAT are physically distinct but closely related quantities ( [[#1.4.1|Section 1.4.1]] and Cross-Chapter Box 2.3).

<div id="footnote-006" class="_idFootnote"></div>

[[#footnote-006-backlink|2]] As old as the longest continuous climate records, which are based on the ice core from EPICA Dome Concordia, Antarctica. Polar ice cores are the only paleoclimatic archive providing direct information on past greenhouse gas concentrations.

<div id="footnote-005" class="_idFootnote"></div>

[[#footnote-005-backlink|3]] The labels of ‘mitigation’, ‘adaptation’ and ‘means of implementation and support’ are provided here for guidance only, with no presumption about the actual legal content of the paragraphs and to what extent they encompass mitigation, adaptation and means of implementation in its entirety.

<div id="footnote-004" class="_idFootnote"></div>

[[#footnote-004-backlink|4]] Paragraph 37b in 19/CMA.1 in FCCC/PA/CMA/2018/3/Add.2, pursuant decision 1/CP.21, paragraph 99 of the adoption of the PA in FCCC/CP/2015/10/Add.1, available at: https://unfccc.int/documents/193408 .

<div id="footnote-003" class="_idFootnote"></div>

[[#footnote-003-backlink|5]] Decision 5/CP.25, available at: [https://unfccc.int/sites/default/files/resource/cp2019_13a01E.pdf https://unfccc.int/sites/default/files/resource/cp2 019_13a01E.pdf] .

<div id="footnote-002" class="_idFootnote"></div>

[[#footnote-002-backlink|6]] Decision 1/CP.23, in FCCC/CP/2017/L.13, available at [https://unfccc.int/resource/docs/2017/cop23/eng/l13.pdf https://unfccc.int/resource/docs/2017/cop 23/eng/l13.pdf] .

<div id="footnote-001" class="_idFootnote"></div>

[[#footnote-001-backlink|7]] Box 1.2 reproduces the temperature metrics as they appeared in the respective SPMs of the Special Reports. In AR6 long-term changes of GMST (global mean surface temperature) and GSAT (global surface air temperature) are considered to be equivalent, differing in uncertainty estimates only (Cross-Chapter Box 2.3).

<div id="footnote-000" class="_idFootnote"></div>

[[#footnote-000-backlink|8]] Note that the 5–95% is a ''very likely'' range (see Box 1.1 on the use of calibrated uncertainty language in AR6), though if this is purely a multi-model likelihood range, it is generally treated as ''likely'' , in the absence of other lines of evidence.