rlacombe/ClimateX · Datasets at Hugging Face

statement_idx int64 0 8.09k	report stringclasses 3 values	page_num int64 18 2.84k	sent_num int64 0 78	statement stringlengths 13 4.29k	confidence stringclasses 4 values	score int64 0 3	split stringclasses 2 values
100	AR6_WGI	66	16	Global ocean heat content continued to increase throughout this period, indicating continuous warming of the entire climate system	very high	3	train
101	AR6_WGI	66	17	Hot extremes also continued to increase during this period over land	high	2	train
102	AR6_WGI	66	18	Even in a continually warming climate, periods of reduced and increased trends in global surface temperature at decadal time scales will continue to occur in the 21st century	very high	3	train
103	AR6_WGI	67	1	Simulations and understanding of modes of climate variability, including teleconnections, have improved since AR5	medium	1	train
104	AR6_WGI	67	3	While anthropogenic forcing has contributed to multi-decadal mean precipitation changes in several regions, internal variability can delay emergence of the anthropogenic signal in long-term precipitation changes in many land regions	high	2	train
105	AR6_WGI	67	6	Several impact-relevant changes have not yet emerged from natural variability but will emerge sooner or later in this century depending on the emissions scenario	high	2	train
106	AR6_WGI	67	7	Ocean acidification and deoxygenation have already emerged over most of the global open ocean, as has a reduction in Arctic sea ice	high	2	train
107	AR6_WGI	68	4	New techniques and analyses drawing on several lines of evidence have provided greater confidence in attributing changes in regional weather and climate extremes to human influence	high	2	train
108	AR6_WGI	68	11	For example, the difference in observed warming trends between cities and their surroundings can partly be attributed to urbanization	very high	3	train
109	AR6_WGI	68	13	Multiple attribution approaches support the contribution of human influence to several regional multi-decadal mean precipitation changes	high	2	train
110	AR6_WGI	68	14	Understanding about past and future changes in weather and climate extremes has increased due to better observation-based datasets, physical understanding of processes, an increasing proportion of scientific literature combining different lines of evidence, and improved accessibility to different types of climate models	high	2	train
111	AR6_WGI	71	8	In SSP1-2.6 and SSP2-4.5, changes in ERF also explain about half of the changes in the range of warming	medium	1	train
112	AR6_WGI	71	9	For SSP5-8.5, higher climate sensitivity is the primary reason behind the upper end of the CMIP6- projected warming being higher than for RCP8.5 in CMIP5	medium	1	train
113	AR6_WGI	71	14	The differences in the few ESMs for which both emissions and concentration-driven runs were available for the same scenario are small and do not affect the assessment of global surface temperature projections discussed in Cross-Section Box TS.1 and Section TS.2	high	2	train
114	AR6_WGI	73	8	Multiple lines of evidence can be used to construct climate information on a global to regional scale and can be further distilled in a co-production process to meet user needs	high	2	train
115	AR6_WGI	73	12	Many global and regional climatic impact-drivers have a direct relation to global warming levels	high	2	train
116	AR6_WGI	75	4	Climate change has already altered CID profiles and resulted in shifting magnitude, frequency, duration, seasonality and spatial extent of associated indices	high	2	train
117	AR6_WGI	75	6	These include heat, cold, wet and dry hazards, both mean and extremes; cryospheric hazards (snow cover, ice extent, permafrost) and oceanic hazards (marine heatwaves)	high	2	train
118	AR6_WGI	75	12	Changes in GMST and GSAT over time differ by at most 10% in either direction	high	2	train
119	AR6_WGI	75	16	Temperatures as high as during the most recent decade (2011–2020) exceed the warmest centennial-scale range reconstructed for the present interglacial, around 6500 years ago [0.2°C to 1°C]	medium	1	train
120	AR6_WGI	75	17	The next most recent warm period was about 125,000 years ago during the last interglacial when the multi-centennial temperature range [0.5°C to 1.5°C] encompasses the 2011–2020 values	medium	1	train
121	AR6_WGI	75	22	Global surface temperature in any individual year could exceed 1.5°C relative to 1850–1900 by 2030 with a likelihood between 40% and 60% across the scenarios considered here	medium	1	train
122	AR6_WGI	75	24	Periods of reduced and increased global surface temperature trends at decadal time scales will continue to occur in the 21st century	very high	3	train
123	AR6_WGI	76	5	It is likely that there was a net anthropogenic forcing of 0.0–0.3 Wm–2 in 1850–1900 relative to 1750	medium	1	train
124	AR6_WGI	76	7	Beginning approximately 6500 years ago, global surface temperature generally decreased, culminating in the coldest multi-century interval of the post-glacial period (since roughly 7000 years ago), which occurred between around 1450 and 1850	high	2	train
125	AR6_WGI	76	8	Over the last 50 years, global surface temperature has increased at an observed rate unprecedented in at least the last two thousand years	high	2	train
126	AR6_WGI	76	9	Temperatures as high as during the most recent decade (2011–2020) exceed the warmest centennial-scale range reconstructed for the present interglacial, around 6500 years ago [0.2°C to 1°C]	medium	1	train
127	AR6_WGI	76	10	The next most recent warm period was about 125,000 years ago during the Last Interglacial when the multi-centennial temperature range [0.5°C to 1.5°C] encompasses the 2011–2020 values	medium	1	train
128	AR6_WGI	76	11	During the mid-Pliocene Warm Period, around 3.3–3.0 million years ago, global surface temperature was 2.5°C to 4°C warmer	medium	1	train
129	AR6_WGI	76	20	Furthermore, the heating of the climate system continued during this period, as reflected in the continued warming of the global ocean (very high confidence) and in the continued rise of hot extremes over land	medium	1	train
130	AR6_WGI	76	21	Since 2012, global surface temperature has risen strongly, with the past five years (2016–2020) being the hottest five-year period between 1850 and 2020	high	2	train
131	AR6_WGI	78	3	Vertical bars are 5–95th percentile ranges of estimated global surface temperature for the Last Interglacial and mid-Holocene	medium	1	train
132	AR6_WGI	78	22	The other half arises because for central estimates of climate sensitivity, most scenarios show stronger warming over the near term than was estimated as ‘current’ in SR1.5	medium	1	train
133	AR6_WGI	78	25	If climate sensitivity lies near the lower end of the assessed very likely range, crossing the 1.5°C warming level is avoided in scenarios SSP1-1.9 and SSP1-2.6	medium	1	train
134	AR6_WGI	78	26	Global surface temperature in any individual year, in contrast to the 20-year average, could by 2030 exceed 1.5°C relative to 1850–1900 with a likelihood between 40% and 60%, across the scenarios considered here	medium	1	train
135	AR6_WGI	78	34	The uncertainty ranges for the period 2081–2100 continue to be dominated by the uncertainty in equilibrium climate sensitivity and transient climate response	very high	3	train
136	AR6_WGI	79	14	Continued GHG emissions greatly increase the likelihood of potentially irreversible changes in the global climate system (Box TS.9), in particular with respect to the contribution of ice sheets to global sea level change	high	2	train
137	AR6_WGI	83	11	Global mean concentrations of anthropogenic aerosols peaked in the late 20th century and have slowly declined since in northern mid-latitudes, although they continue to increase in South Asia and East Africa	high	2	train
138	AR6_WGI	83	12	The total anthropogenic effective radiative forcing (ERF) in 2019, relative to 1750, was 2.72 [1.96 to 3.48] W m–2	medium	1	train
139	AR6_WGI	83	14	The average magnitude and variability of volcanic aerosols since 1900 has not been unusual compared to at least the past 2500 years	medium	1	train
140	AR6_WGI	85	2	The centennial rate of change of CO 2 since 1850 has no precedent in at least the past 800,000 years (Figure TS.9), and the fastest rates of change over the last 56 million years were at least a factor of four lower	low	0	train
141	AR6_WGI	85	6	The increase since 1750 of 1137 ± 10 ppb (157.8%) far exceeds the range over multiple glacial–interglacial transitions of the past 800,000 years	high	2	train
142	AR6_WGI	85	12	N 2O concentration trends since 1980 are largely driven by a 30% increase in emissions from the expansion and intensification of global agriculture	high	2	train
143	AR6_WGI	85	16	Abundances of HFCs, which are replacements for CFCs and HCFCs, are increasing	high	2	train
144	AR6_WGI	85	19	Ice cores show increases in aerosols across the Northern Hemisphere mid-latitudes since 1700 and reductions since the late 20th century	high	2	train
145	AR6_WGI	85	20	Aerosol optical depth (AOD), derived from satellite- and ground-based radiometers, has decreased since 2000 over the mid-latitude continents of both hemispheres, but increased over South Asia and East Africa	high	2	train
146	AR6_WGI	85	22	Global carbonaceous aerosol budgets and trends remain poorly characterized due to limited observations, but black carbon (BC), a warming aerosol component, is declining in several regions of the Northern Hemisphere	low	0	train
147	AR6_WGI	85	23	Total aerosol ERF in 2019, relative to 1750, is −1.1 [−1.7 to −0.4] W m−2	medium	1	train
148	AR6_WGI	85	25	Since the mid-20th century, tropospheric ozone surface concentrations have increased by 30–70% across the Northern Hemisphere	medium	1	train
149	AR6_WGI	85	26	Future changes in surface ozone concentrations will be primarily driven by changes in precursor emissions rather than climate change	high	2	train
150	AR6_WGI	85	27	Stratospheric ozone has declined between 60°S–60°N by 2.2% from 1964–1980 to 2014–2017	high	2	train
151	AR6_WGI	85	31	Model estimates suggest no significant change in oxidizing capacity from 1850 to 1980	low	0	test
152	AR6_WGI	86	6	The proportion of tropical cyclones that are intense is expected to increase (high confidence), but the total global number of tropical cyclones is expected to decrease or remain unchanged	medium	1	train
153	AR6_WGI	87	2	In the tropics, since at least 2001 (when new techniques permit more robust quantification), the upper troposphere has warmed faster than the near-surface	medium	1	train
154	AR6_WGI	87	6	This has been accompanied by a strengthening of the Hadley Circulation in the Northern Hemisphere	medium	1	train
155	AR6_WGI	87	7	It is likely that human influence has contributed to the poleward expansion of the zonal mean Hadley cell in the Southern Hemisphere since the 1980s, which is projected to further expand with global warming	high	2	train
156	AR6_WGI	87	26	The frequency of intense extratropical cyclones is projected to decrease	medium	1	train
157	AR6_WGI	87	27	Projected changes in the intensity depend on the resolution of climate models	medium	1	test
158	AR6_WGI	88	6	With increasing global warming, some very rare extremes and some compound events (multivariate or concurrent extremes) with low likelihood in past and current climate will become more frequent, and there is a higher chance that events unprecedented in the observational record occur	high	2	train
159	AR6_WGI	88	25	Continued Amazon deforestation, combined with a warming climate, raises the probability that this ecosystem will cross a tipping point into a dry state during the 21st century	low	0	train
160	AR6_WGI	89	5	Compound events and concurrent extremes contribute to increasing probability of low-likelihood, high-impact outcomes and will become more frequent with increasing global warming	high	2	train
161	AR6_WGI	90	1	Over the past four to six decades, it is virtually certain that the global ocean has warmed, with human influence extremely likely the main driver since the 1970s, making climate change irreversible over centuries to millennia	medium	1	train
162	AR6_WGI	90	4	A long-term increase in surface open ocean pH occurred over the past 50 million years, and surface ocean pH as low as recent times is uncommon in the last 2 million years	medium	1	test
163	AR6_WGI	90	8	Stratification (virtually certain), acidification (virtually certain), deoxygenation (high confidence) and marine heatwave frequency	high	2	train
164	AR6_WGI	90	11	The ocean is currently warming faster than at any other time since at least the last deglacial transition (medium confidence), with warming extending to depths well below 2000 m	very high	3	train
165	AR6_WGI	90	14	Ocean warming is irreversible over centuries to millennia, but the magnitude of warming is scenario-dependent from about the mid-21st century	medium	1	test
166	AR6_WGI	90	15	The warming will not be globally uniform, with heat primarily stored in Southern Ocean water-masses and weaker warming in the subpolar North Atlantic	high	2	train
167	AR6_WGI	90	18	Marine heatwaves have become more frequent over the 20th century (high confidence), approximately doubling in frequency (high confidence) and becoming more intense and longer since the 1980s	medium	1	train
168	AR6_WGI	90	24	It is extremely likely that human influence has contributed to this salinity change and that the large-scale pattern will grow in amplitude over the 21st century	medium	1	train
169	AR6_WGI	90	27	Direct observational records since the mid-2000s are too short to determine the relative contributions of internal variability, natural forcing and anthropogenic forcing to AMOC change	high	2	train
170	AR6_WGI	90	31	Western boundary currents and subtropical gyres have shifted poleward since 1993	medium	1	train
171	AR6_WGI	90	32	Subtropical gyres, the East Australian Current Extension, the Agulhas Current, and the Brazil Current are projected to intensify in the 21st century in response to changes in wind stress, while the Gulf Stream and the Indonesian Throughflow are projected to weaken	medium	1	train
172	AR6_WGI	90	33	All of the four main eastern boundary upwelling systems are projected to weaken at low latitudes and intensify at high latitudes in the 21st century	high	2	train
173	AR6_WGI	92	1	Ocean acidification and associated reductions in the saturation state of calcium carbonate – a constituent of skeletons or shells of a variety of marine organisms – is expected to increase in the 21st century under all emissions scenarios	high	2	train
174	AR6_WGI	92	2	A long-term increase in surface open ocean pH occurred over the past 50 million years (high confidence), and surface ocean pH as low as recent times is uncommon in the last 2 million years	medium	1	train
175	AR6_WGI	92	4	Over the past 2–3 decades, a pH decline in the ocean interior has been observed in all ocean basins	high	2	train
176	AR6_WGI	92	6	Deoxygenation is projected to continue to increase with ocean warming	high	2	train
177	AR6_WGI	92	9	The range of a smaller subset of organisms has shifted equatorward and to shallower depths	high	2	train
178	AR6_WGI	92	10	Phenological metrics associated with the life cycles of many organisms have also changed over the last two decades or longer	high	2	train
179	AR6_WGI	92	16	The Arctic Ocean is projected to become practically sea ice-free in late summer under high CO 2 emissions scenarios by the end of the 21st century	high	2	train
180	AR6_WGI	92	18	Glaciers will continue to lose mass at least for several decades even if global temperature is stabilized	very high	3	train
181	AR6_WGI	92	21	Since the late 1970s, Arctic sea ice area and thickness have decreased in both summer and winter, with sea ice becoming younger, thinner and more dynamic	very high	3	train
182	AR6_WGI	92	22	It is very likely that anthropogenic forcing, mainly due to greenhouse gas increases, was the main driver of this loss, although new evidence suggests that anthropogenic aerosol forcing has offset part of the greenhouse gas-induced losses since the 1950s	medium	1	train
183	AR6_WGI	92	24	This practically sea ice-free state will become the norm for late summer by the end of the 21st century in high CO 2 emissions scenarios	high	2	train
184	AR6_WGI	92	25	Arctic summer sea ice varies approximately linearly with global surface temperature, implying that there is no tipping point and observed/ projected losses are potentially reversible	high	2	train
185	AR6_WGI	92	29	For each additional 1°C of warming (up to 4°C above the 1850–1900 level), the global volume of perennially frozen ground to 3 m below the surface is projected to decrease by about 25% relative to the present volume	medium	1	train
186	AR6_WGI	92	30	However, these decreases may be underestimated due to an incomplete representation of relevant physical processes in ESMs	low	0	train
187	AR6_WGI	93	3	Under RCP2.6 and RCP8.5, respectively, glaciers are projected to lose 18% ± 13% and 36% ± 20% of their current mass over the 21st century	medium	1	train
188	AR6_WGI	93	6	It is virtually certain that the Greenland Ice Sheet has lost mass since the 1990s, with human influence a contributing factor	medium	1	train
189	AR6_WGI	93	10	Projections of future Greenland ice-mass loss (Box TS.4, Table 1; Figure TS.11e) are dominated by increased surface melt under all emissions scenarios	high	2	train
190	AR6_WGI	93	13	The total Antarctic ice mass losses were dominated by the West Antarctic Ice Sheet, with combined West Antarctic and Peninsula annual loss rates increasing since about 2000	very high	3	test
191	AR6_WGI	93	16	Mass losses from West Antarctic outlet glaciers, mainly induced by ice shelf basal melt (high confidence), outpace mass gain from increased snow accumulation on the continent	very high	3	train
192	AR6_WGI	93	22	Human activities were very likely the main driver of observed GMSL rise since 1971, and new observational evidence leads to an assessed sea level rise over the period 1901 to 2018 that is consistent with the sum of individual components contributing to sea level rise, including expansion due to ocean warming and melting of glaciers and ice sheets	high	2	train
193	AR6_WGI	93	24	Sea level responds to greenhouse gas (GHG) emissions more slowly than global surface temperature, leading to weaker scenario dependence over the 21st century than for global surface temperature	high	2	train
194	AR6_WGI	93	25	This slow response also leads to long-term committed sea level rise, associated with ongoing ocean heat uptake and the slow adjustment of the ice sheets, that will continue over the centuries and millennia following cessation of emissions	high	2	train
195	AR6_WGI	93	26	By 2100, GMSL is projected to rise by 0.28– 0.55 m (likely range) under SSP1-1.9 and 0.63–1.01 m (likely range) under SSP5-8.5 relative to the 1995–2014 average	medium	1	train
196	AR6_WGI	93	33	New analyses and paleo-evidence since AR5 show this rate is very likely faster than during any century over at least the last three millennia	high	2	train
197	AR6_WGI	93	34	Since AR5, there is strengthened evidence for an increase in the rate of GMSL rise since the mid-20th century, with an average rate of 2.3 [1.6–3.1] mm yr–1 over the period 1971–2018 increasing to 3.7 [3.2–4.2] mm yr–1 for the period 2006–2018	high	2	test
198	AR6_WGI	95	11	By 2300, GMSL will rise 0.3–3.1 m under low CO 2 emissions (SSP1-2.6)	low	0	train
199	AR6_WGI	95	12	Under high CO 2 emissions (SSP5-8.5), projected GMSL rise is between 1.7 and 6.8 m by 2300 in the absence of MICI and by up to 16 m considering MICI	low	0	train

100

AR6_WGI

66

16

Global ocean heat content continued to increase throughout this period, indicating continuous warming of the entire climate system

very high

3

train

101

AR6_WGI

66

17

Hot extremes also continued to increase during this period over land

high

2

train

102

AR6_WGI

66

18

Even in a continually warming climate, periods of reduced and increased trends in global surface temperature at decadal time scales will continue to occur in the 21st century

very high

3

train

103

AR6_WGI

67

1

Simulations and understanding of modes of climate variability, including teleconnections, have improved since AR5

medium

1

train

104

AR6_WGI

67

3

While anthropogenic forcing has contributed to multi-decadal mean precipitation changes in several regions, internal variability can delay emergence of the anthropogenic signal in long-term precipitation changes in many land regions

high

2

train

105

AR6_WGI

67

6

Several impact-relevant changes have not yet emerged from natural variability but will emerge sooner or later in this century depending on the emissions scenario

high

2

train

106

AR6_WGI

67

7

Ocean acidification and deoxygenation have already emerged over most of the global open ocean, as has a reduction in Arctic sea ice

high

2

train

107

AR6_WGI

68

4

New techniques and analyses drawing on several lines of evidence have provided greater confidence in attributing changes in regional weather and climate extremes to human influence

high

2

train

108

AR6_WGI

68

11

For example, the difference in observed warming trends between cities and their surroundings can partly be attributed to urbanization

very high

3

train

109

AR6_WGI

68

13

Multiple attribution approaches support the contribution of human influence to several regional multi-decadal mean precipitation changes

high

2

train

110

AR6_WGI

68

14

Understanding about past and future changes in weather and climate extremes has increased due to better observation-based datasets, physical understanding of processes, an increasing proportion of scientific literature combining different lines of evidence, and improved accessibility to different types of climate models

high

2

train

111

AR6_WGI

71

8

In SSP1-2.6 and SSP2-4.5, changes in ERF also explain about half of the changes in the range of warming

medium

1

train

112

AR6_WGI

71

9

For SSP5-8.5, higher climate sensitivity is the primary reason behind the upper end of the CMIP6- projected warming being higher than for RCP8.5 in CMIP5

medium

1

train

113

AR6_WGI

71

14

The differences in the few ESMs for which both emissions and concentration-driven runs were available for the same scenario are small and do not affect the assessment of global surface temperature projections discussed in Cross-Section Box TS.1 and Section TS.2

high

2

train

114

AR6_WGI

73

8

Multiple lines of evidence can be used to construct climate information on a global to regional scale and can be further distilled in a co-production process to meet user needs

high

2

train

115

AR6_WGI

73

12

Many global and regional climatic impact-drivers have a direct relation to global warming levels

high

2

train

116

AR6_WGI

75

4

Climate change has already altered CID profiles and resulted in shifting magnitude, frequency, duration, seasonality and spatial extent of associated indices

high

2

train

117

AR6_WGI

75

6

These include heat, cold, wet and dry hazards, both mean and extremes; cryospheric hazards (snow cover, ice extent, permafrost) and oceanic hazards (marine heatwaves)

high

2

train

118

AR6_WGI

75

12

Changes in GMST and GSAT over time differ by at most 10% in either direction

high

2

train

119

AR6_WGI

75

16

Temperatures as high as during the most recent decade (2011–2020) exceed the warmest centennial-scale range reconstructed for the present interglacial, around 6500 years ago [0.2°C to 1°C]

medium

1

train

120

AR6_WGI

75

17

The next most recent warm period was about 125,000 years ago during the last interglacial when the multi-centennial temperature range [0.5°C to 1.5°C] encompasses the 2011–2020 values

medium

1

train

121

AR6_WGI

75

22

Global surface temperature in any individual year could exceed 1.5°C relative to 1850–1900 by 2030 with a likelihood between 40% and 60% across the scenarios considered here

medium

1

train

122

AR6_WGI

75

24

Periods of reduced and increased global surface temperature trends at decadal time scales will continue to occur in the 21st century

very high

3

train

123

AR6_WGI

76

5

It is likely that there was a net anthropogenic forcing of 0.0–0.3 Wm–2 in 1850–1900 relative to 1750

medium

1

train

124

AR6_WGI

76

7

Beginning approximately 6500 years ago, global surface temperature generally decreased, culminating in the coldest multi-century interval of the post-glacial period (since roughly 7000 years ago), which occurred between around 1450 and 1850

high

2

train

125

AR6_WGI

76

8

Over the last 50 years, global surface temperature has increased at an observed rate unprecedented in at least the last two thousand years

high

2

train

126

AR6_WGI

76

9

Temperatures as high as during the most recent decade (2011–2020) exceed the warmest centennial-scale range reconstructed for the present interglacial, around 6500 years ago [0.2°C to 1°C]

medium

1

train

127

AR6_WGI

76

10

The next most recent warm period was about 125,000 years ago during the Last Interglacial when the multi-centennial temperature range [0.5°C to 1.5°C] encompasses the 2011–2020 values

medium

1

train

128

AR6_WGI

76

11

During the mid-Pliocene Warm Period, around 3.3–3.0 million years ago, global surface temperature was 2.5°C to 4°C warmer

medium

1

train

129

AR6_WGI

76

20

Furthermore, the heating of the climate system continued during this period, as reflected in the continued warming of the global ocean (very high confidence) and in the continued rise of hot extremes over land

medium

1

train

130

AR6_WGI

76

21

Since 2012, global surface temperature has risen strongly, with the past five years (2016–2020) being the hottest five-year period between 1850 and 2020

high

2

train

131

AR6_WGI

78

3

Vertical bars are 5–95th percentile ranges of estimated global surface temperature for the Last Interglacial and mid-Holocene

medium

1

train

132

AR6_WGI

78

22

The other half arises because for central estimates of climate sensitivity, most scenarios show stronger warming over the near term than was estimated as ‘current’ in SR1.5

medium

1

train

133

AR6_WGI

78

25

If climate sensitivity lies near the lower end of the assessed very likely range, crossing the 1.5°C warming level is avoided in scenarios SSP1-1.9 and SSP1-2.6

medium

1

train

134

AR6_WGI

78

26

Global surface temperature in any individual year, in contrast to the 20-year average, could by 2030 exceed 1.5°C relative to 1850–1900 with a likelihood between 40% and 60%, across the scenarios considered here

medium

1

train

135

AR6_WGI

78

34

The uncertainty ranges for the period 2081–2100 continue to be dominated by the uncertainty in equilibrium climate sensitivity and transient climate response

very high

3

train

136

AR6_WGI

79

14

Continued GHG emissions greatly increase the likelihood of potentially irreversible changes in the global climate system (Box TS.9), in particular with respect to the contribution of ice sheets to global sea level change

high

2

train

137

AR6_WGI

83

11

Global mean concentrations of anthropogenic aerosols peaked in the late 20th century and have slowly declined since in northern mid-latitudes, although they continue to increase in South Asia and East Africa

high

2

train

138

AR6_WGI

83

12

The total anthropogenic effective radiative forcing (ERF) in 2019, relative to 1750, was 2.72 [1.96 to 3.48] W m–2

medium

1

train

139

AR6_WGI

83

14

The average magnitude and variability of volcanic aerosols since 1900 has not been unusual compared to at least the past 2500 years

medium

1

train

140

AR6_WGI

85

2

The centennial rate of change of CO 2 since 1850 has no precedent in at least the past 800,000 years (Figure TS.9), and the fastest rates of change over the last 56 million years were at least a factor of four lower

low

0

train

141

AR6_WGI

85

6

The increase since 1750 of 1137 ± 10 ppb (157.8%) far exceeds the range over multiple glacial–interglacial transitions of the past 800,000 years

high

2

train

142

AR6_WGI

85

12

N 2O concentration trends since 1980 are largely driven by a 30% increase in emissions from the expansion and intensification of global agriculture

high

2

train

143

AR6_WGI

85

16

Abundances of HFCs, which are replacements for CFCs and HCFCs, are increasing

high

2

train

144

AR6_WGI

85

19

Ice cores show increases in aerosols across the Northern Hemisphere mid-latitudes since 1700 and reductions since the late 20th century

high

2

train

145

AR6_WGI

85

20

Aerosol optical depth (AOD), derived from satellite- and ground-based radiometers, has decreased since 2000 over the mid-latitude continents of both hemispheres, but increased over South Asia and East Africa

high

2

train

146

AR6_WGI

85

22

Global carbonaceous aerosol budgets and trends remain poorly characterized due to limited observations, but black carbon (BC), a warming aerosol component, is declining in several regions of the Northern Hemisphere

low

0

train

147

AR6_WGI

85

23

Total aerosol ERF in 2019, relative to 1750, is −1.1 [−1.7 to −0.4] W m−2

medium

1

train

148

AR6_WGI

85

25

Since the mid-20th century, tropospheric ozone surface concentrations have increased by 30–70% across the Northern Hemisphere

medium

1

train

149

AR6_WGI

85

26

Future changes in surface ozone concentrations will be primarily driven by changes in precursor emissions rather than climate change

high

2

train

150

AR6_WGI

85

27

Stratospheric ozone has declined between 60°S–60°N by 2.2% from 1964–1980 to 2014–2017

high

2

train

151

AR6_WGI

85

31

Model estimates suggest no significant change in oxidizing capacity from 1850 to 1980

low

0

test

152

AR6_WGI

86

6

The proportion of tropical cyclones that are intense is expected to increase (high confidence), but the total global number of tropical cyclones is expected to decrease or remain unchanged

medium

1

train

153

AR6_WGI

87

2

In the tropics, since at least 2001 (when new techniques permit more robust quantification), the upper troposphere has warmed faster than the near-surface

medium

1

train

154

AR6_WGI

87

6

This has been accompanied by a strengthening of the Hadley Circulation in the Northern Hemisphere

medium

1

train

155

AR6_WGI

87

7

It is likely that human influence has contributed to the poleward expansion of the zonal mean Hadley cell in the Southern Hemisphere since the 1980s, which is projected to further expand with global warming

high

2

train

156

AR6_WGI

87

26

The frequency of intense extratropical cyclones is projected to decrease

medium

1

train

157

AR6_WGI

87

27

Projected changes in the intensity depend on the resolution of climate models

medium

1

test

158

AR6_WGI

88

6

With increasing global warming, some very rare extremes and some compound events (multivariate or concurrent extremes) with low likelihood in past and current climate will become more frequent, and there is a higher chance that events unprecedented in the observational record occur

high

2

train

159

AR6_WGI

88

25

Continued Amazon deforestation, combined with a warming climate, raises the probability that this ecosystem will cross a tipping point into a dry state during the 21st century

low

0

train

160

AR6_WGI

89

5

Compound events and concurrent extremes contribute to increasing probability of low-likelihood, high-impact outcomes and will become more frequent with increasing global warming

high

2

train

161

AR6_WGI

90

1

Over the past four to six decades, it is virtually certain that the global ocean has warmed, with human influence extremely likely the main driver since the 1970s, making climate change irreversible over centuries to millennia

medium

1

train

162

AR6_WGI

90

4

A long-term increase in surface open ocean pH occurred over the past 50 million years, and surface ocean pH as low as recent times is uncommon in the last 2 million years

medium

1

test

163

AR6_WGI

90

8

Stratification (virtually certain), acidification (virtually certain), deoxygenation (high confidence) and marine heatwave frequency

high

2

train

164

AR6_WGI

90

11

The ocean is currently warming faster than at any other time since at least the last deglacial transition (medium confidence), with warming extending to depths well below 2000 m

very high

3

train

165

AR6_WGI

90

14

Ocean warming is irreversible over centuries to millennia, but the magnitude of warming is scenario-dependent from about the mid-21st century

medium

1

test

166

AR6_WGI

90

15

The warming will not be globally uniform, with heat primarily stored in Southern Ocean water-masses and weaker warming in the subpolar North Atlantic

high

2

train

167

AR6_WGI

90

18

Marine heatwaves have become more frequent over the 20th century (high confidence), approximately doubling in frequency (high confidence) and becoming more intense and longer since the 1980s

medium

1

train

168

AR6_WGI

90

24

It is extremely likely that human influence has contributed to this salinity change and that the large-scale pattern will grow in amplitude over the 21st century

medium

1

train

169

AR6_WGI

90

27

Direct observational records since the mid-2000s are too short to determine the relative contributions of internal variability, natural forcing and anthropogenic forcing to AMOC change

high

2

train

170

AR6_WGI

90

31

Western boundary currents and subtropical gyres have shifted poleward since 1993

medium

1

train

171

AR6_WGI

90

32

Subtropical gyres, the East Australian Current Extension, the Agulhas Current, and the Brazil Current are projected to intensify in the 21st century in response to changes in wind stress, while the Gulf Stream and the Indonesian Throughflow are projected to weaken

medium

1

train

172

AR6_WGI

90

33

All of the four main eastern boundary upwelling systems are projected to weaken at low latitudes and intensify at high latitudes in the 21st century

high

2

train

173

AR6_WGI

92

1

Ocean acidification and associated reductions in the saturation state of calcium carbonate – a constituent of skeletons or shells of a variety of marine organisms – is expected to increase in the 21st century under all emissions scenarios

high

2

train

174

AR6_WGI

92

2

A long-term increase in surface open ocean pH occurred over the past 50 million years (high confidence), and surface ocean pH as low as recent times is uncommon in the last 2 million years

medium

1

train

175

AR6_WGI

92

4

Over the past 2–3 decades, a pH decline in the ocean interior has been observed in all ocean basins

high

2

train

176

AR6_WGI

92

6

Deoxygenation is projected to continue to increase with ocean warming

high

2

train

177

AR6_WGI

92

9

The range of a smaller subset of organisms has shifted equatorward and to shallower depths

high

2

train

178

AR6_WGI

92

10

Phenological metrics associated with the life cycles of many organisms have also changed over the last two decades or longer

high

2

train

179

AR6_WGI

92

16

The Arctic Ocean is projected to become practically sea ice-free in late summer under high CO 2 emissions scenarios by the end of the 21st century

high

2

train

180

AR6_WGI

92

18

Glaciers will continue to lose mass at least for several decades even if global temperature is stabilized

very high

3

train

181

AR6_WGI

92

21

Since the late 1970s, Arctic sea ice area and thickness have decreased in both summer and winter, with sea ice becoming younger, thinner and more dynamic

very high

3

train

182

AR6_WGI

92

22

It is very likely that anthropogenic forcing, mainly due to greenhouse gas increases, was the main driver of this loss, although new evidence suggests that anthropogenic aerosol forcing has offset part of the greenhouse gas-induced losses since the 1950s

medium

1

train

183

AR6_WGI

92

24

This practically sea ice-free state will become the norm for late summer by the end of the 21st century in high CO 2 emissions scenarios

high

2

train

184

AR6_WGI

92

25

Arctic summer sea ice varies approximately linearly with global surface temperature, implying that there is no tipping point and observed/ projected losses are potentially reversible

high

2

train

185

AR6_WGI

92

29

For each additional 1°C of warming (up to 4°C above the 1850–1900 level), the global volume of perennially frozen ground to 3 m below the surface is projected to decrease by about 25% relative to the present volume

medium

1

train

186

AR6_WGI

92

30

However, these decreases may be underestimated due to an incomplete representation of relevant physical processes in ESMs

low

0

train

187

AR6_WGI

93

3

Under RCP2.6 and RCP8.5, respectively, glaciers are projected to lose 18% ± 13% and 36% ± 20% of their current mass over the 21st century

medium

1

train

188

AR6_WGI

93

6

It is virtually certain that the Greenland Ice Sheet has lost mass since the 1990s, with human influence a contributing factor

medium

1

train

189

AR6_WGI

93

10

Projections of future Greenland ice-mass loss (Box TS.4, Table 1; Figure TS.11e) are dominated by increased surface melt under all emissions scenarios

high

2

train

190

AR6_WGI

93

13

The total Antarctic ice mass losses were dominated by the West Antarctic Ice Sheet, with combined West Antarctic and Peninsula annual loss rates increasing since about 2000

very high

3

test

191

AR6_WGI

93

16

Mass losses from West Antarctic outlet glaciers, mainly induced by ice shelf basal melt (high confidence), outpace mass gain from increased snow accumulation on the continent

very high

3

train

192

AR6_WGI

93

22

Human activities were very likely the main driver of observed GMSL rise since 1971, and new observational evidence leads to an assessed sea level rise over the period 1901 to 2018 that is consistent with the sum of individual components contributing to sea level rise, including expansion due to ocean warming and melting of glaciers and ice sheets

high

2

train

193

AR6_WGI

93

24

Sea level responds to greenhouse gas (GHG) emissions more slowly than global surface temperature, leading to weaker scenario dependence over the 21st century than for global surface temperature

high

2

train

194

AR6_WGI

93

25

This slow response also leads to long-term committed sea level rise, associated with ongoing ocean heat uptake and the slow adjustment of the ice sheets, that will continue over the centuries and millennia following cessation of emissions

high

2

train

195

AR6_WGI

93

26

By 2100, GMSL is projected to rise by 0.28– 0.55 m (likely range) under SSP1-1.9 and 0.63–1.01 m (likely range) under SSP5-8.5 relative to the 1995–2014 average

medium

1

train

196

AR6_WGI

93

33

New analyses and paleo-evidence since AR5 show this rate is very likely faster than during any century over at least the last three millennia

high

2

train

197

AR6_WGI

93

34

Since AR5, there is strengthened evidence for an increase in the rate of GMSL rise since the mid-20th century, with an average rate of 2.3 [1.6–3.1] mm yr–1 over the period 1971–2018 increasing to 3.7 [3.2–4.2] mm yr–1 for the period 2006–2018

high

2

test

198

AR6_WGI

95

11

By 2300, GMSL will rise 0.3–3.1 m under low CO 2 emissions (SSP1-2.6)

low

0

train

199

AR6_WGI

95

12

Under high CO 2 emissions (SSP5-8.5), projected GMSL rise is between 1.7 and 6.8 m by 2300 in the absence of MICI and by up to 16 m considering MICI

low

0

train