IPCC:AR6/WGI/Chapter-2 - Revision history

Laura at 12:01, 22 June 2026

2026-06-22T12:01:37Z

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Laura at 12:00, 22 June 2026

2026-06-22T12:00:58Z

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Laura: /* Executive Summary */

2026-06-22T11:40:28Z

Executive Summary

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	Figure 2.1 ~~'''~~\|~~''' '''~~Visual guide to Chapter 2.'''		'''Figure 2.1 \| Visual guide to Chapter 2.'''

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Laura: /* FAQ 2.1 | The Earth’s Temperature Has Varied Before. How Is the Current Warming Any Different? */

2026-06-22T11:24:18Z

FAQ 2.1 | The Earth’s Temperature Has Varied Before. How Is the Current Warming Any Different?

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	'''FAQ 2.1, Figure 1 \|''' '''Evidence for the unusualness of recent warming.'''		'''FAQ 2.1, Figure 1 \|''' '''Evidence for the unusualness of recent warming.'''

Laura: /* 2.3.5 Synthesis of Evidence for Past Changes */

2026-06-22T11:23:11Z

2.3.5 Synthesis of Evidence for Past Changes

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	Cross-Chapter Box 2.4 \| ~~'''~~The Climate of the Pliocene (Around 3 Million Years Ago), When CO~~'''~~ <sub>2</sub> ~~'''~~Concentrations Were Last Similar to Those of the Present Day~~'''~~		== Cross-Chapter Box 2.4 \| The Climate of the Pliocene (Around 3 Million Years Ago), When CO <sub>2</sub> Concentrations Were Last Similar to Those of the Present Day ==

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	~~Cross-Chapter Box 2.4~~

	[[File:786f2f20cf88c829470d1f013112b0db IPCC_AR6_WGI_CCBox_2_4_Figure_1.png]]		[[File:786f2f20cf88c829470d1f013112b0db IPCC_AR6_WGI_CCBox_2_4_Figure_1.png]]

	'''Cross-Chapter Box 2.4, ~~Figur'''~~		'''Cross-Chapter Box 2.4, Figure 1 \|''' '''Climate indicators of the mid-Pliocene Warm Period (MPWP; 3.3–3.0 million years ago, Ma) from models and proxy data. (a)''' Simulated surface air temperature (left) and precipitation rate anomaly (right) anomaly (relative to 1850–1900) from the Pliocene Model Intercomparison Project Phase 2 multi-model mean, including CMIP6 (n = 4) and non-CMIP6 (n = 12) models. Symbols represent site-level proxy-based estimates of sea-surface temperature for KM5c (n = 32), and terrestrial temperature (n = 8) and precipitation rate for the MPWP (n = 8). '''(b)''' Distribution of terrestrial biomes was considerably different during the Piacenzian Stage (3.6–2.6 Ma) (upper) compared with present-day (lower). Biome distributions simulated with a model (BIOME4) in which Pliocene biome classifications are based on 208 locations, with model-predicted biomes filling spatial gaps, and the present day, with the model adjusted for CO <sub>2</sub> concentration of 324 parts per million (ppm). '''(c)''' Ice-sheet extent predicted using modelled climate forcing and showing where multiple models consistently predict the former presence or absence of ice on Greenland (n = 8 total) and Antarctica (n = 10 total). Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).

	~~'''e~~ 1 \|'''

	'''Climate indicators of the mid-Pliocene Warm Period (MPWP; 3.3–3.0 million years ago, Ma) from models and proxy data. (a)''' Simulated surface air temperature (left) and precipitation rate anomaly (right) anomaly (relative to 1850–1900) from the Pliocene Model Intercomparison Project Phase 2 multi-model mean, including CMIP6 (n = 4) and non-CMIP6 (n = 12) models. Symbols represent site-level proxy-based estimates of sea-surface temperature for KM5c (n = 32), and terrestrial temperature (n = 8) and precipitation rate for the MPWP (n = 8). '''(b)''' Distribution of terrestrial biomes was considerably different during the Piacenzian Stage (3.6–2.6 Ma) (upper) compared with present-day (lower). Biome distributions simulated with a model (BIOME4) in which Pliocene biome classifications are based on 208 locations, with model-predicted biomes filling spatial gaps, and the present day, with the model adjusted for CO <sub>2</sub> concentration of 324 parts per million (ppm). '''(c)''' Ice-sheet extent predicted using modelled climate forcing and showing where multiple models consistently predict the former presence or absence of ice on Greenland (n = 8 total) and Antarctica (n = 10 total). Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).

	'''Northern high latitudes'''		'''Northern high latitudes'''
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	During the MPWP (3.3–3.0 Ma) the atmospheric CO <sub>2</sub> concentration was similar to present, and the slow-response, large-scale indicators reflect a world that was warmer than present. With ''very high confidence'' , relative to present, global surface temperature, sea level, and precipitation rate were higher, NH latitudinal temperature gradient was lower, and major terrestrial biomes expanded poleward. With ''medium confidence'' from proxy-based evidence alone ([[#2.3.2\|Section 2.3.2]]), combined with numerical modelling, analysis of the sea-level budget, and process understanding (Section 9.6.2), there is ''high confidence'' that cryospheric indicators were diminished. There is ''medium confidence'' that the Pacific longitudinal temperature gradient was weaker and monsoon systems were stronger.		During the MPWP (3.3–3.0 Ma) the atmospheric CO <sub>2</sub> concentration was similar to present, and the slow-response, large-scale indicators reflect a world that was warmer than present. With ''very high confidence'' , relative to present, global surface temperature, sea level, and precipitation rate were higher, NH latitudinal temperature gradient was lower, and major terrestrial biomes expanded poleward. With ''medium confidence'' from proxy-based evidence alone ([[#2.3.2\|Section 2.3.2]]), combined with numerical modelling, analysis of the sea-level budget, and process understanding (Section 9.6.2), there is ''high confidence'' that cryospheric indicators were diminished. There is ''medium confidence'' that the Pacific longitudinal temperature gradient was weaker and monsoon systems were stronger.
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Laura: /* 2.3.1.4.5 Stratospheric polar vortex and sudden warming events */

2026-06-22T11:20:34Z

2.3.1.4.5 Stratospheric polar vortex and sudden warming events

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	~~'''~~Cross-Chapter Box 2.3 \| New Estimates of Global Warming to Date, and Key Implications~~'''~~		== Cross-Chapter Box 2.3 \| New Estimates of Global Warming to Date, and Key Implications ==

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	This Cross-Chapter Box presents the AR6 WGI assessment of observed global warming and describes improvements and updates since AR5 and subsequent Special Reports. The revised estimates result from: the availability of new and revised observational datasets; the occurrence of recent record warm years; and the evaluation of the two primary metrics used to estimate global warming in past IPCC reports: ‘Global mean surface temperature’ (GMST) and ‘Global surface air temperature’ (GSAT). Implications for threshold crossing times, remaining carbon budgets and impacts assessments across AR6 WGs are discussed.		This Cross-Chapter Box presents the AR6 WGI assessment of observed global warming and describes improvements and updates since AR5 and subsequent Special Reports. The revised estimates result from: the availability of new and revised observational datasets; the occurrence of recent record warm years; and the evaluation of the two primary metrics used to estimate global warming in past IPCC reports: ‘Global mean surface temperature’ (GMST) and ‘Global surface air temperature’ (GSAT). Implications for threshold crossing times, remaining carbon budgets and impacts assessments across AR6 WGs are discussed.

	~~Cross-Chapter Box 2.3~~

	'''Dataset innovations'''		'''Dataset innovations'''
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	[[File:0eb5647470256cf45e0ca85e9ee7fe91 IPCC_AR6_WGI_CCBox_2_3_Figure_1.png]]		[[File:0eb5647470256cf45e0ca85e9ee7fe91 IPCC_AR6_WGI_CCBox_2_3_Figure_1.png]]

	'''Cross-chapter Box 2.3, Figure 1'''		'''Cross-chapter Box 2.3, Figure 1''' '''\|''' '''Changes in assessed historical surface temperature changes since AR5. (a)''' Summary of the impact of various steps from AR5 assessment warming-to-date number for 1880–2012 using a linear trend fit to the AR6 assessment based upon the difference between 1850–1900 and 2011–2020. Whiskers provide 90% (''very likely'') ranges. AR6 assessment in addition denotes additional warming since the period around 1750 (Cross-Chapter Box 1.2). '''(b)''' Time series of the average of assessed AR5 series (orange, faint prior to 1880 when only HadCRUT4 was available) and AR6 assessed series (blue) and their differences (offset) including an illustration of the two trend fitting metrics used in AR5 and AR6. Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).

	'''\|'''

	'''Changes in assessed historical surface temperature changes since AR5. (a)''' Summary of the impact of various steps from AR5 assessment warming-to-date number for 1880–2012 using a linear trend fit to the AR6 assessment based upon the difference between 1850–1900 and 2011–2020. Whiskers provide 90% (''very likely'') ranges. AR6 assessment in addition denotes additional warming since the period around 1750 (Cross-Chapter Box 1.2). '''(b)''' Time series of the average of assessed AR5 series (orange, faint prior to 1880 when only HadCRUT4 was available) and AR6 assessed series (blue) and their differences (offset) including an illustration of the two trend fitting metrics used in AR5 and AR6. Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).

	'''Observed changes in global mean temperature since the pre-industrial era'''		'''Observed changes in global mean temperature since the pre-industrial era'''
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	There is a significant issue in areas where sea ice melts or grows, where the quantity used in observational-based GMST estimates switches between air temperature and sea surface temperature. This primarily affects analyses combining SAT anomalies over land and ice with SST anomalies over ocean. In areas where sea ice has recently melted, the climatological value changes from an air-temperature based estimate to an SST estimate based upon the freezing point of seawater (–1.8°C). This switch in climatology to, in general, a warmer climatology, leads to a bias towards reduced warming in anomalies compared with analyses based on absolute temperatures. [[#Richardson--2018\|Richardson et al. (2018)]] found this underestimation to amount to approximately 3% of observed warming in historical model simulations. Given the projected future sea ice losses, the effect will grow in future (''low confidence''), with potential effects of the order of 0.1°C in the second half of the 21st century under high warming scenarios, although with some uncertainty arising from the large spread of sea ice loss in model projections ([[#Tokarska--2019\|Tokarska et al., 2019]]).		There is a significant issue in areas where sea ice melts or grows, where the quantity used in observational-based GMST estimates switches between air temperature and sea surface temperature. This primarily affects analyses combining SAT anomalies over land and ice with SST anomalies over ocean. In areas where sea ice has recently melted, the climatological value changes from an air-temperature based estimate to an SST estimate based upon the freezing point of seawater (–1.8°C). This switch in climatology to, in general, a warmer climatology, leads to a bias towards reduced warming in anomalies compared with analyses based on absolute temperatures. [[#Richardson--2018\|Richardson et al. (2018)]] found this underestimation to amount to approximately 3% of observed warming in historical model simulations. Given the projected future sea ice losses, the effect will grow in future (''low confidence''), with potential effects of the order of 0.1°C in the second half of the 21st century under high warming scenarios, although with some uncertainty arising from the large spread of sea ice loss in model projections ([[#Tokarska--2019\|Tokarska et al., 2019]]).

	'''Cross Chapter Box 2.3, Table'''		'''Cross Chapter Box 2.3, Table''' '''1 \|''' '''Summary of key observationally based global warming estimates (in °C) to various reference periods in the present report and selected prior reports (AR5 WGI and SR1.5) and their principal applications (see [[IPCC:Wg1:Chapter:Chapter-1#1.4.1\|Section 1.4.1]] for further information on reference periods).''' Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).

	'''1 \|'''

	'''Summary of key observationally based global warming estimates (in °C) to various reference periods in the present report and selected prior reports (AR5 WGI and SR1.5) and their principal applications (see [[IPCC:Wg1:Chapter:Chapter-1#1.4.1\|Section 1.4.1]] for further information on reference periods).''' Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).
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	There is therefore ''high confidence'' that assessment of the magnitude and timing of impacts-related climate quantities at 1.5°C is not substantially affected by the revised estimate of historical global warming. The assessment of the implications of limiting global warming to 1.5°C compared to 2°C will also remain broadly unchanged by the updated estimate of historical warming, as this depends on the relative impacts rather than the absolute impacts at any specific definition of global temperature anomaly (''high confidence'').		There is therefore ''high confidence'' that assessment of the magnitude and timing of impacts-related climate quantities at 1.5°C is not substantially affected by the revised estimate of historical global warming. The assessment of the implications of limiting global warming to 1.5°C compared to 2°C will also remain broadly unchanged by the updated estimate of historical warming, as this depends on the relative impacts rather than the absolute impacts at any specific definition of global temperature anomaly (''high confidence'').
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Laura: /* 2.3 Changes in Large-scale Climate */

2026-06-22T11:17:39Z

2.3 Changes in Large-scale Climate

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	Cross-Chapter Box 2.2 \| ~~'''~~Large-scale Indicators of Climate Change~~'''~~		== Cross-Chapter Box 2.2 \| Large-scale Indicators of Climate Change ==

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	Monitoring surface temperatures is integral to the negotiations of UNFCCC and the global mean temperature goals of the Paris Agreement. Upper-air temperatures are a key indicator of different causal mechanisms underlying climate change and underpinned the very first conclusion in the Second Assessment Report of a ‘discernible human influence’ ([[#Santer--1996\|Santer et al., 1996]]). To ascertain large-scale changes of and human influence on the global hydrological cycle (which includes terrestrial and oceanic components), a small subset of indicators across this cycle are chosen: ocean and land precipitation–evaporation (P–E), global precipitation, total column water vapour, surface humidity (specific and relative), and global river runoff. [[IPCC:Wg1:Chapter:Chapter-8\|Chapter 8]] performs a substantive and holistic assessment of a much broader range of components. Finally, a warming world may be accompanied by a change in large-scale circulation patterns linked through energy/mass/momentum constraints such as the extent and strength of the Hadley circulation (HC), monsoon systems, and/or the position and strength of the sub-tropical and polar jets.		Monitoring surface temperatures is integral to the negotiations of UNFCCC and the global mean temperature goals of the Paris Agreement. Upper-air temperatures are a key indicator of different causal mechanisms underlying climate change and underpinned the very first conclusion in the Second Assessment Report of a ‘discernible human influence’ ([[#Santer--1996\|Santer et al., 1996]]). To ascertain large-scale changes of and human influence on the global hydrological cycle (which includes terrestrial and oceanic components), a small subset of indicators across this cycle are chosen: ocean and land precipitation–evaporation (P–E), global precipitation, total column water vapour, surface humidity (specific and relative), and global river runoff. [[IPCC:Wg1:Chapter:Chapter-8\|Chapter 8]] performs a substantive and holistic assessment of a much broader range of components. Finally, a warming world may be accompanied by a change in large-scale circulation patterns linked through energy/mass/momentum constraints such as the extent and strength of the Hadley circulation (HC), monsoon systems, and/or the position and strength of the sub-tropical and polar jets.

	'''Cross-Chapter Box 2.2, Table 1'''		'''Cross-Chapter Box 2.2, Table 1''' '''\|''' '''Summary of the large-scale indicators used across Chapters 2 through 4 and their principal applications in remaining chapters.''' Indicators are sub-divided by Earth-system domain and their inclusion in individual chapters is indicated by a blue dot. The list of additional chapters is limited to those where the variable is a principal consideration.

	'''\|'''

	'''Summary of the large-scale indicators used across Chapters 2 through 4 and their principal applications in remaining chapters.''' Indicators are sub-divided by Earth-system domain and their inclusion in individual chapters is indicated by a blue dot. The list of additional chapters is limited to those where the variable is a principal consideration.
	[[File:929de268f15ce15bbbbbc63d5e236f60 IPCC_AR6_WGI_Chapter_2_CCB_2_2_Table_1.png]]		[[File:929de268f15ce15bbbbbc63d5e236f60 IPCC_AR6_WGI_Chapter_2_CCB_2_2_Table_1.png]]

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	Many modes of climate variability affect global, hemispheric or regional climate across a range of timescales. Conversely, their behaviour may be influenced by global climate change. Modes were selected for inclusion that: (i) have effects at large spatial scales; and (ii) have substantial potential to modify interannual to multi-decadal climate. The selected modes are considered in multiple chapters (Cross-Chapter Box 2.2, Table 2) and are defined in Annex IV.		Many modes of climate variability affect global, hemispheric or regional climate across a range of timescales. Conversely, their behaviour may be influenced by global climate change. Modes were selected for inclusion that: (i) have effects at large spatial scales; and (ii) have substantial potential to modify interannual to multi-decadal climate. The selected modes are considered in multiple chapters (Cross-Chapter Box 2.2, Table 2) and are defined in Annex IV.

	'''Cross-Chapter Box 2.2, Table'''		'''Cross-Chapter Box 2.2, Table''' '''2 \|''' '''Summary of the modes of variability used across Chapters 2 through 4 and their principal applications in remaining chapters.''' Inclusion in each of Chapters 2 through 4 is indicated by a blue dot of the relevant table cell. The list of remaining chapters is limited to those where the mode of variability is a principal consideration of that chapter and is not intended to be exhaustive.

	~~'''2 \|'''~~

	'''Summary of the modes of variability used across Chapters 2 through 4 and their principal applications in remaining chapters.''' Inclusion in each of Chapters 2 through 4 is indicated by a blue dot of the relevant table cell. The list of remaining chapters is limited to those where the mode of variability is a principal consideration of that chapter and is not intended to be exhaustive.
	[[File:483d30c6811ec81fc3df5eff165bffb5 IPCC_AR6_WGI_Chapter_2_CCB_2_2_Table_2.png]]		[[File:483d30c6811ec81fc3df5eff165bffb5 IPCC_AR6_WGI_Chapter_2_CCB_2_2_Table_2.png]]
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	== 2.4 Changes in Modes of Variability ==		== 2.4 Changes in Modes of Variability ==

Laura: /* 2.2.3.3 Modern Measurements of WMGHGs */

2026-06-22T11:15:56Z

2.2.3.3 Modern Measurements of WMGHGs

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	Table 2.2 ~~'''~~\|''' '''Atmospheric global annual mean mixing ratios (dry-air mole fraction) for well-mixed greenhouse gases.''' The table provides observed values for 2011 and 2019, and relative changes since 2011, for selected well-mixed, radiatively important gases (ERF >0.001 W m <sup>–2</sup>), estimated from various measurement networks or compilations. Units are parts per million (ppm) for CO <sub>2</sub> , parts per billion (ppb) for CH <sub>4</sub> and N <sub>2</sub> O, parts per trillion (ppt) for all other gases. Time series since 1750, data for additional gases, references, and network information can be found in [[IPCC:Wg1:Chapter:Annex-iii\|Annex III]] and the corresponding electronic supplement. Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).		'''Table 2.2 \|''' '''Atmospheric global annual mean mixing ratios (dry-air mole fraction) for well-mixed greenhouse gases.''' The table provides observed values for 2011 and 2019, and relative changes since 2011, for selected well-mixed, radiatively important gases (ERF >0.001 W m <sup>–2</sup>), estimated from various measurement networks or compilations. Units are parts per million (ppm) for CO <sub>2</sub> , parts per billion (ppb) for CH <sub>4</sub> and N <sub>2</sub> O, parts per trillion (ppt) for all other gases. Time series since 1750, data for additional gases, references, and network information can be found in [[IPCC:Wg1:Chapter:Annex-iii\|Annex III]] and the corresponding electronic supplement. Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).

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Laura: /* Cross-Chapter Box 2.1 | Paleoclimate Reference Periods in the Assessment Report */

2026-06-22T11:15:14Z

Cross-Chapter Box 2.1 | Paleoclimate Reference Periods in the Assessment Report

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	GMST estimated for each of the reference periods based on proxy evidence ([[#2.3.1.1\|Section 2.3.1.1]]) can be compared with climate projections over coming centuries to place the range of possible futures into a longer-term context (Cross-Chapter Box 2.1, Figure 1). Here, the ''very likely'' range of GMST for the warmer world reference periods are compared with the ''very likely'' range of GSAT projected for the end the 21st century (2080–2100; Table 4.5) and the ''likely'' range for the end of the 23rd century (2300; Table 4.9) under multiple Shared Socio-economic Pathway (SSP) scenarios. From this comparison, there is ''medium confidence'' in the following: GMST estimated for the warmest long-term period of the Last Interglacial about 125 ka (125,000 years ago; 0.5°C–1.5°C relative to 1850–1900) overlaps with the low end of the range of temperatures projected under SSP1-2.6 including its negative emissions extension to the end of the 23rd century (1.0°C to 2.2°C). GMST estimated for a period of prolonged warmth during the mid-Pliocene Warm Period about 3 Ma [2.5°C to 4.0°C] is similar to temperatures projected under SSP2-4.5 for the end of the 23rd century (2.3°C to 4.6°C). GMST estimated for the Miocene Climatic Optimum [5°C to 10°C] and Early Eocene Climatic Optimum [10°C to 18°C], about 15 and 50 Ma, respectively, overlap with the range projected for the end of the 23rd century under SSP5-8.5 (6.6°C to 14.1°C) ''.''		GMST estimated for each of the reference periods based on proxy evidence ([[#2.3.1.1\|Section 2.3.1.1]]) can be compared with climate projections over coming centuries to place the range of possible futures into a longer-term context (Cross-Chapter Box 2.1, Figure 1). Here, the ''very likely'' range of GMST for the warmer world reference periods are compared with the ''very likely'' range of GSAT projected for the end the 21st century (2080–2100; Table 4.5) and the ''likely'' range for the end of the 23rd century (2300; Table 4.9) under multiple Shared Socio-economic Pathway (SSP) scenarios. From this comparison, there is ''medium confidence'' in the following: GMST estimated for the warmest long-term period of the Last Interglacial about 125 ka (125,000 years ago; 0.5°C–1.5°C relative to 1850–1900) overlaps with the low end of the range of temperatures projected under SSP1-2.6 including its negative emissions extension to the end of the 23rd century (1.0°C to 2.2°C). GMST estimated for a period of prolonged warmth during the mid-Pliocene Warm Period about 3 Ma [2.5°C to 4.0°C] is similar to temperatures projected under SSP2-4.5 for the end of the 23rd century (2.3°C to 4.6°C). GMST estimated for the Miocene Climatic Optimum [5°C to 10°C] and Early Eocene Climatic Optimum [10°C to 18°C], about 15 and 50 Ma, respectively, overlap with the range projected for the end of the 23rd century under SSP5-8.5 (6.6°C to 14.1°C) ''.''

	~~Cross-Chapter Box 2.1~~

	'''Cross-Chapter Box 2.1, Table 1 \|''' '''Paleo-reference periods, listed from oldest to youngest.''' See ‘AR6 Sections’ (right-hand column) for literature citations related to each ‘Sketch of the climate state.’ See WGII (Chapters 1, 2 and 3) for citations related to paleontological changes. See Interactive [[IPCC:Wg1:Chapter:Atlas\|Atlas]] for simulated climate variables for MPWP, LIG, LGM and MH.		'''Cross-Chapter Box 2.1, Table 1 \|''' '''Paleo-reference periods, listed from oldest to youngest.''' See ‘AR6 Sections’ (right-hand column) for literature citations related to each ‘Sketch of the climate state.’ See WGII (Chapters 1, 2 and 3) for citations related to paleontological changes. See Interactive [[IPCC:Wg1:Chapter:Atlas\|Atlas]] for simulated climate variables for MPWP, LIG, LGM and MH.

Laura: /* 2.1 Introduction */

2026-06-22T11:14:59Z

2.1 Introduction

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	~~'''~~Cross-Chapter Box 2.1 \| Paleoclimate Reference Periods in the Assessment Report~~'''~~		== Cross-Chapter Box 2.1 \| Paleoclimate Reference Periods in the Assessment Report ==

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	Cross-Chapter Box 2.1		Cross-Chapter Box 2.1

	'''Cross-Chapter Box 2.1, Table 1~~'''~~		'''Cross-Chapter Box 2.1, Table 1 \|''' '''Paleo-reference periods, listed from oldest to youngest.''' See ‘AR6 Sections’ (right-hand column) for literature citations related to each ‘Sketch of the climate state.’ See WGII (Chapters 1, 2 and 3) for citations related to paleontological changes. See Interactive [[IPCC:Wg1:Chapter:Atlas\|Atlas]] for simulated climate variables for MPWP, LIG, LGM and MH.

	~~'''~~\|'''

	'''Paleo-reference periods, listed from oldest to youngest.''' See ‘AR6 Sections’ (right-hand column) for literature citations related to each ‘Sketch of the climate state.’ See WGII (Chapters 1, 2 and 3) for citations related to paleontological changes. See Interactive [[IPCC:Wg1:Chapter:Atlas\|Atlas]] for simulated climate variables for MPWP, LIG, LGM and MH.
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	'''Global mean surface temperature (GMST) over the past 60 million years (60 Myr) relative to 1850–1900 shown on three time scales.''' Information about each of the nine paleo reference periods (blue font) and sections in AR6 that discuss these periods are listed in Cross-Chapter Box 2.1 Table 1. Grey horizontal bars at the top mark important events. Characteristic uncertainties are based on expert judgement and are representative of the approximate midpoint of their respective time scales; uncertainties decrease forward in time. GMST estimates for most paleo reference periods (Figure 2.34) overlap with this reconstruction, but take into account multiple lines of evidence. Future projections span the range of global surface air temperature best estimates for SSP1–2.6 and SSP5–8.5 scenarios described in [[IPCC:Wg1:Chapter:Chapter-1#1.6\|Section 1.6]] . Range shown for 2100 is based on CMIP6 multi-model mean for 2081–2100 from Table 4.5; range for 2300 is based upon an emulator and taken from Table 4.9. Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).		'''Global mean surface temperature (GMST) over the past 60 million years (60 Myr) relative to 1850–1900 shown on three time scales.''' Information about each of the nine paleo reference periods (blue font) and sections in AR6 that discuss these periods are listed in Cross-Chapter Box 2.1 Table 1. Grey horizontal bars at the top mark important events. Characteristic uncertainties are based on expert judgement and are representative of the approximate midpoint of their respective time scales; uncertainties decrease forward in time. GMST estimates for most paleo reference periods (Figure 2.34) overlap with this reconstruction, but take into account multiple lines of evidence. Future projections span the range of global surface air temperature best estimates for SSP1–2.6 and SSP5–8.5 scenarios described in [[IPCC:Wg1:Chapter:Chapter-1#1.6\|Section 1.6]] . Range shown for 2100 is based on CMIP6 multi-model mean for 2081–2100 from Table 4.5; range for 2300 is based upon an emulator and taken from Table 4.9. Further details on data sources and processing are available in the chapter data table (Table 2.SM.1).
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