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
500	AR6_WGI	203	24	By contrast, Antarctic sea ice extent overall saw no statistically significant trend for the period 1979–2018	high	2	train
501	AR6_WGI	204	1	It also found evidence for an increase in the annual global proportion of Category 4 or 5 tropical cyclones in recent decades	low	0	train
502	AR6_WGI	204	4	The natural response of land to human-induced environmental change – such as increasing atmospheric CO 2 concentration, nitrogen deposition and climate change – caused a net CO 2 sink equivalent of around 29% of total CO 2 emissions (medium confidence); however, the persistence of the sink is uncertain due to climate change	high	2	train
503	AR6_WGI	204	7	However, the report estimated that the resulting net effect on globally averaged surface temperature was small over the historical period	medium	1	train
504	AR6_WGI	204	8	The SROCC found that the carbon content of Arctic and boreal permafrost is almost twice that of the atmosphere	medium	1	train
505	AR6_WGI	204	9	Projections of climate change The SR1.5 concluded that global warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate	high	2	train
506	AR6_WGI	204	11	The SR1.5 also found that reaching and sustaining net zero anthropogenic CO 2 emissions and reducing net non-CO 2 radiative forcing would halt anthropogenic global warming on multi-decadal time scales	high	2	train
507	AR6_WGI	204	12	The maximum temperature reached is then determined by (i) cumulative net global anthropogenic CO 2 emissions up to the time of net zero CO 2 emissions (high confidence) and (ii) the level of non-CO 2 radiative forcing in the decades prior to the time that maximum temperatures are reached	medium	1	train
508	AR6_WGI	204	13	Furthermore, climate models project robust differences in regional climate characteristics between the present day and a global warming of 1.5°C, and between 1.5°C and 2°C, including mean temperature in most land and ocean regions and hot extremes in most inhabited regions	high	2	train
509	AR6_WGI	204	15	The SROCC projected that global-scale glacier mass loss, permafrost thaw, and decline in snow cover and Arctic sea ice extent will continue in the period 2031–2050 due to surface air temperature increases	high	2	train
510	AR6_WGI	204	16	The Greenland and Antarctic ice sheets are projected to lose mass at an increasing rate throughout the 21st century and beyond	high	2	train
511	AR6_WGI	204	19	For the RCP8.5 scenario, projections of GMSL rise by 2100 are higher by 0.1 m than in AR5 due to a larger contribution from the Antarctic Ice Sheet	medium	1	train
512	AR6_WGI	204	20	Extreme sea level events that occurred once per hundred years in the recent past are projected to occur at least once per year at many locations by 2050, especially in tropical regions, under all RCP scenarios	high	2	train
513	AR6_WGI	204	21	According to SR1.5, by 2100 GMSL rise would be around 0.1 m lower with 1.5°C global warming compared to 2°C	medium	1	train
514	AR6_WGI	204	23	However, instability and/or irreversible loss of the Greenland and Antarctic ice sheets, resulting in a multi-metre rise in sea level over hundreds to thousands of years, could be triggered at 1.5°C–2°C of global warming	medium	1	train
515	AR6_WGI	204	24	According to SROCC, sea level rise in an extended RCP2.6 scenario would be limited to around 1 m in 2300 (low confidence) while under RCP8.5 multi-metre sea level rise is projected by then	medium	1	train
516	AR6_WGI	204	25	The SROCC projected that over the 21st century, the ocean will transition to unprecedented conditions, with increased temperatures (virtually certain), further acidification (virtually certain), and oxygen decline	medium	1	train
517	AR6_WGI	204	26	Marine heatwaves are projected to become more frequent (very high confidence) as are extreme El Niño and La Niña events	medium	1	train
518	AR6_WGI	205	20	Starting from year 2018, the remaining carbon budget for a one-in-two (50%) chance of limiting global warming to 1.5°C is about 580 GtCO 2, and about 420 GtCO 2 for a two-in-three (66%) chance	medium	1	train
519	AR6_WGI	205	22	Using GMST instead of GSAT gives estimates of 770 GtCO 2 and 570 GtCO 2, respectively	medium	1	train
520	AR6_WGI	209	1	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
521	AR6_WGI	209	11	Combining these different sources of evidence, we assess that from the period around 1750 to 1850–1900 there was a change in global temperature of around 0.1 [–0.1 to +0.3] °C (medium confidence), with an anthropogenic component in a likely range of 0.0°C–0.2°C	medium	1	train
522	AR6_WGI	212	15	Overall, tropical regions show earlier emergence of temperature changes than at higher latitudes	high	2	train
523	AR6_WGI	227	7	In summary, the observational coverage of ongoing changes to the climate system is improved at the time of AR6, relative to what was available for AR5	high	2	train
524	AR6_WGI	228	2	Overall, the number, temporal resolution and chronological accuracy of paleoclimate reconstructions have increased since AR5, leading to improved understanding of climate system processes (or Earth system processes)	high	2	train
525	AR6_WGI	228	28	In summary, while the quantity, quality and diversity of climate system observations have grown since AR5, the loss or potential loss of several critical components of the observational network is also evident	high	2	train
526	AR6_WGI	230	6	In summary, the improvements in atmospheric reanalyses, and the greater number of years since the routine ingestion of satellite data began, relative to AR5, mean that there is increased confidence in using atmospheric reanalysis products alongside more standard observation-based datasets in AR6	high	2	train
527	AR6_WGI	231	10	In summary, reanalyses have improved since AR5 and can increasingly be used as a line of evidence in assessments of the state and evolution of the climate system	high	2	train
528	AR6_WGI	239	1	Overall, we assess that increases in computing power and the broader availability of larger and more varied ensembles of model simulations have contributed to better estimations of uncertainty in projections of future change	high	2	train
529	AR6_WGI	297	25	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	2	train
530	AR6_WGI	298	24	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	2	train
531	AR6_WGI	298	26	The average rate of sea level rise was 1.3 [0.6 to 2.1] mm yr–1 between 1901 and 1971, increasing to 1.9 [0.8 to 2.9] mm yr–1 between 1971 and 2006, and further increasing to 3.7 [3.2 to 4.2] mm yr–1 between 2006 and 2018	high	2	train
532	AR6_WGI	299	1	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	2	train
533	AR6_WGI	299	5	The observed average rate of heating of the climate system increased from 0.50 [0.32 to 0.69] W m–2 for the period 1971–2006 to 0.79 [0.52 to 1.06] W m–2 for the period 2006– 2018	high	2	train
534	AR6_WGI	299	6	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	2	train
535	AR6_WGI	299	10	The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification.In 2019, atmospheric CO 2 concentrations were higher than at any time in at least 2 million years (high confidence), and concentrations of CH 4 and N 2O were higher than at any time in at least 800,000 years	very high	3	train
536	AR6_WGI	299	11	Since 1750, increases in CO 2 (47%) and CH 4 (156%) concentrations far exceed – and increases in N 2O (23%) are similar to – the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years	very high	3	train
537	AR6_WGI	300	11	In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years	medium	1	train
538	AR6_WGI	300	12	Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years	high	2	train
539	AR6_WGI	300	13	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	1	train
540	AR6_WGI	300	14	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	1	train
541	AR6_WGI	300	16	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	2	train
542	AR6_WGI	300	17	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	1	train
543	AR6_WGI	300	18	A long- term increase in surface open ocean pH occurred over the past 50 million years	high	2	train
544	AR6_WGI	300	19	However, surface open ocean pH as low as recent decades is unusual in the last 2 million years	medium	1	train
545	AR6_WGI	302	4	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	1	train
546	AR6_WGI	302	5	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	0	train
547	AR6_WGI	306	9	Present-day global concentrations of atmospheric carbon dioxide (CO 2) are at higher levels than at any time in at least the past two million years	high	2	train
548	AR6_WGI	306	10	Changes in ERF since the late 19th century are dominated by increases in concentrations of greenhouse gases and trends in aerosols; the net ERF is positive and changing at an increasing rate since the 1970s	medium	1	test
549	AR6_WGI	306	12	Solar activity since 1900 was high but not exceptional compared to the past 9000 years	high	2	train
550	AR6_WGI	306	13	The average magnitude and variability of volcanic aerosol forcing since 1900 have not been unusual compared to the past 2500 years	medium	1	train
551	AR6_WGI	306	17	These changes are larger than those between glacial and interglacial periods over the last 800,000 years for CO 2 and CH 4 and of comparable magnitude for N 2O	very high	3	train
552	AR6_WGI	306	21	Aerosol optical depth (AOD) has decreased since 2000 over Northern Hemisphere mid-latitudes and Southern Hemisphere mid-latitude continents, but increased over South Asia and East Africa	high	2	train
553	AR6_WGI	306	25	Stratospheric ozone has declined between 60°S and 60°N by 2.2% from the 1980s to 2014–2017	high	2	train
554	AR6_WGI	306	26	Since the mid-20th century, tropospheric ozone has increased by 30–70% across the Northern Hemisphere	medium	1	train
555	AR6_WGI	306	27	Since the mid-1990s, free tropospheric ozone increases were 2–7% per decade in the northern mid-latitudes (high confidence), 2–12% per decade in the tropics (high confidence) and <5% per decade in southern mid-latitudes	medium	1	train
556	AR6_WGI	306	31	The best-estimate ERF from the increase in global albedo is –0.15 W m–2 since 1700 and –0.12 W m–2 since 1850	medium	1	test
557	AR6_WGI	306	33	Over the past several decades, key indicators of the climate system are increasingly at levels unseen in centuries to millennia, and are changing at rates unprecedented in at least the last 2000 years	high	2	train
558	AR6_WGI	306	34	Temperatures as high as during the most recent decade (2011–2020) exceed the warmest centennial-scale range reconstructed for the present interglacial, around 6,500 years ago [0.2°C–1°C relative to 1850–1900]	medium	1	train
559	AR6_WGI	306	35	The next older warm period is the last interglacial when the multi-centennial temperature range about 125,000 years ago [0.5°C–1.5°C relative to 1850–1900] encompassed the recent decade values	medium	1	train
560	AR6_WGI	306	40	Over the last 50 years, observed GMST has increased at a rate unprecedented in at least the last 2000 years	high	2	train
561	AR6_WGI	307	4	In the Tropics, the upper troposphere has warmed faster than the near-surface since at least 2001, the period over which new observational techniques permit more robust quantification	medium	1	train
562	AR6_WGI	307	8	Global land precipitation has likely increased since 1950, with a faster increase since the 1980s	medium	1	train
563	AR6_WGI	307	15	Global monsoon precipitation has likely increased since the 1980s, mainly in the Northern Hemisphere	medium	1	train
564	AR6_WGI	307	20	Between 1979 and 2019, Arctic sea ice area has decreased in both summer and winter, with sea ice becoming younger, thinner and more dynamic	very high	3	train
565	AR6_WGI	307	22	Antarctic sea ice area has experienced little net change since 1979	high	2	train
566	AR6_WGI	307	24	Reductions in spring snow cover extent have occurred across the Northern Hemisphere since at least 1978	very high	3	train
567	AR6_WGI	307	25	With few exceptions, glaciers have retreated since the second half of the 19th century and have continued to retreat at increased rates since the 1990s (very high confidence); this behaviour is unprecedented in at least the last 2000 years	medium	1	train
568	AR6_WGI	307	26	Greenland Ice Sheet (GrIS) mass loss has increased substantially since 2000	high	2	train
569	AR6_WGI	307	27	The Greenland Ice Sheet was smaller than at present during the Last Interglacial period (high confidence) and the mid-Holocene	high	2	train
570	AR6_WGI	307	28	The Antarctic Ice Sheet (AIS) lost mass between 1992 and 2020 (very high confidence), with an increasing rate of mass loss over this period	medium	1	train
571	AR6_WGI	307	29	Although permafrost persists in areas of the Northern Hemisphere where it was absent prior to 3000 years ago, increases in temperatures in the upper 30 m over the past three to four decades have been widespread	high	2	train
572	AR6_WGI	307	32	The average rate of sea level rise was 1.3 [0.6 to 2.1] mm yr –1 between 1901 and 1971, increasing to 1.9 [0.8 to 2.9] mm yr –1 between 1971 and 2006, and further increasing to 3.7 [3.2 to 4.2] mm yr –1 between 2006 and 2018	high	2	test
573	AR6_WGI	307	35	Since 1971, it is virtually certain that global ocean heat content has increased for the upper (0–700 m) layer, very likely for the intermediate (700–2000 m) layer and likely below 2000 m, and is currently increasing faster than at any point since at least the last deglacial transition (18 to 11 thousand years ago)	medium	1	train
574	AR6_WGI	307	37	The Atlantic Meridional Overturning Circulation (AMOC) was relatively stable during the past 8000 years (medium confidence) but declined during the 20th century	low	0	train
575	AR6_WGI	307	38	Ocean pH has declined globally at the surface over the past four decades (virtually certain) and in all ocean basins in the ocean interior	high	2	train
576	AR6_WGI	307	39	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
577	AR6_WGI	308	1	Oxygen minimum zones are expanding at many locations	high	2	train
578	AR6_WGI	308	3	The ranges of many marine organisms are shifting towards the poles and towards greater depths	high	2	train
579	AR6_WGI	308	4	This mismatch in responses across species means that the species composition of ecosystems is changing	medium	1	train
580	AR6_WGI	308	5	At multiple locations, various phenological metrics for marine organisms have changed in the last 50 years, with the nature of the changes varying with location and with species	high	2	train
581	AR6_WGI	308	6	In the last two decades, the concentration of phytoplankton at the base of the marine food web, as indexed by chlorophyll concentration, has shown weak and variable trends in low and mid-latitudes and an increase in high latitudes	medium	1	train
582	AR6_WGI	308	7	Global marine primary production decreased slightly from 1998–2018, with increasing production in the Arctic	medium	1	train
583	AR6_WGI	308	9	Over the last century, there have been increases in species turnover within many ecosystems	high	2	test
584	AR6_WGI	308	10	Over the past half century, climate zones have shifted poleward, accompanied by an increase in the length of the growing season in the Northern Hemisphere extratropics and an increase in the amplitude of the seasonal cycle of atmospheric CO 2 above 45°N	high	2	train
585	AR6_WGI	308	11	Since the early 1980s, there has been a global-scale increase in the greenness of the terrestrial surface	high	2	train
586	AR6_WGI	308	13	CO2 levels during the MPWP were similar to present for a sustained period, within a range of 360–420 ppm	medium	1	test
587	AR6_WGI	308	14	Relative to the present, GMST, GMSL and precipitation rate were all higher, the Northern Hemisphere latitudinal temperature gradient was lower, and major terrestrial biomes were shifted northward	very high	3	train
588	AR6_WGI	308	22	Both polar annular modes have exhibited strong positive trends toward increased zonality of mid-latitude circulation over multi-decadal periods, but these trends have not been sustained for the Northern Annular Mode since the early 1990s	high	2	train
589	AR6_WGI	308	23	For tropical ocean modes, a sustained shift beyond multi-centennial variability has not been observed for El Niño–Southern Oscillation	medium	1	train
590	AR6_WGI	308	24	Modes of decadal and multi-decadal variability over the Pacific and Atlantic oceans exhibit no significant trends over the period of observational records	high	2	train
591	AR6_WGI	314	1	To conclude, solar activity since the late 19th century was relatively high but not exceptional in the context of the past 9 kyr	high	2	train
592	AR6_WGI	314	25	However, the average magnitude and variability of SAOD and its associated volcanic aerosol forcing since 1900 are not unusual in the context of at least the past 2.5 kyr	medium	1	train
593	AR6_WGI	315	13	Based on boron and carbon isotope data, supported by other proxies (Hollis et al., 2019), atmospheric CO2 during the EECO (50 Ma) was between 1150 and 2500 ppm	medium	1	test
594	AR6_WGI	316	6	High-resolution sampling (about 1 sample per 3 kyr) with the boron-isotope proxy indicates mean CO 2 mixing ratios for the Marine Isotope Stage KM5c interglacial were 360–420 ppm	medium	1	train
595	AR6_WGI	316	21	Although ice core records present low-pass filtered time series due to gas diffusion and gradual bubble close- off in the snow layer over the ice sheet (Fourteau et al., 2020), the rate of increase since 1850 CE (about 125 ppm increase over about 170 years) is far greater than implied for any 170-year period by ice core records that cover the last 800 ka	very high	3	train
596	AR6_WGI	319	15	The last time CO 2 concentrations were similar to the present-day was over 2 Ma	high	2	train
597	AR6_WGI	319	18	Between 1750–2019 mixing ratios increased by 131.6 ± 2.9 ppm (47%), 1137 ± 10 ppb (156%), and 62 ± 6 ppb (23%), for CO 2, CH 4, and N 2O, respectively	very high	3	train
598	AR6_WGI	323	29	In summary, limited available isotopic evidence constrains the global tropospheric ozone increase to less than 40% between 1850 and 2005	low	0	train
599	AR6_WGI	323	30	Based on sparse historical surface/low altitude data tropospheric ozone has increased since the mid-20th century by 30–70% across the NH	medium	1	train

500

AR6_WGI

203

24

By contrast, Antarctic sea ice extent overall saw no statistically significant trend for the period 1979–2018

high

2

train

501

AR6_WGI

204

1

It also found evidence for an increase in the annual global proportion of Category 4 or 5 tropical cyclones in recent decades

low

0

train

502

AR6_WGI

204

4

The natural response of land to human-induced environmental change – such as increasing atmospheric CO 2 concentration, nitrogen deposition and climate change – caused a net CO 2 sink equivalent of around 29% of total CO 2 emissions (medium confidence); however, the persistence of the sink is uncertain due to climate change

high

2

train

503

AR6_WGI

204

7

However, the report estimated that the resulting net effect on globally averaged surface temperature was small over the historical period

medium

1

train

504

AR6_WGI

204

8

The SROCC found that the carbon content of Arctic and boreal permafrost is almost twice that of the atmosphere

medium

1

train

505

AR6_WGI

204

9

Projections of climate change The SR1.5 concluded that global warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate

high

2

train

506

AR6_WGI

204

11

The SR1.5 also found that reaching and sustaining net zero anthropogenic CO 2 emissions and reducing net non-CO 2 radiative forcing would halt anthropogenic global warming on multi-decadal time scales

high

2

train

507

AR6_WGI

204

12

The maximum temperature reached is then determined by (i) cumulative net global anthropogenic CO 2 emissions up to the time of net zero CO 2 emissions (high confidence) and (ii) the level of non-CO 2 radiative forcing in the decades prior to the time that maximum temperatures are reached

medium

1

train

508

AR6_WGI

204

13

Furthermore, climate models project robust differences in regional climate characteristics between the present day and a global warming of 1.5°C, and between 1.5°C and 2°C, including mean temperature in most land and ocean regions and hot extremes in most inhabited regions

high

2

train

509

AR6_WGI

204

15

The SROCC projected that global-scale glacier mass loss, permafrost thaw, and decline in snow cover and Arctic sea ice extent will continue in the period 2031–2050 due to surface air temperature increases

high

2

train

510

AR6_WGI

204

16

The Greenland and Antarctic ice sheets are projected to lose mass at an increasing rate throughout the 21st century and beyond

high

2

train

511

AR6_WGI

204

19

For the RCP8.5 scenario, projections of GMSL rise by 2100 are higher by 0.1 m than in AR5 due to a larger contribution from the Antarctic Ice Sheet

medium

1

train

512

AR6_WGI

204

20

Extreme sea level events that occurred once per hundred years in the recent past are projected to occur at least once per year at many locations by 2050, especially in tropical regions, under all RCP scenarios

high

2

train

513

AR6_WGI

204

21

According to SR1.5, by 2100 GMSL rise would be around 0.1 m lower with 1.5°C global warming compared to 2°C

medium

1

train

514

AR6_WGI

204

23

However, instability and/or irreversible loss of the Greenland and Antarctic ice sheets, resulting in a multi-metre rise in sea level over hundreds to thousands of years, could be triggered at 1.5°C–2°C of global warming

medium

1

train

515

AR6_WGI

204

24

According to SROCC, sea level rise in an extended RCP2.6 scenario would be limited to around 1 m in 2300 (low confidence) while under RCP8.5 multi-metre sea level rise is projected by then

medium

1

train

516

AR6_WGI

204

25

The SROCC projected that over the 21st century, the ocean will transition to unprecedented conditions, with increased temperatures (virtually certain), further acidification (virtually certain), and oxygen decline

medium

1

train

517

AR6_WGI

204

26

Marine heatwaves are projected to become more frequent (very high confidence) as are extreme El Niño and La Niña events

medium

1

train

518

AR6_WGI

205

20

Starting from year 2018, the remaining carbon budget for a one-in-two (50%) chance of limiting global warming to 1.5°C is about 580 GtCO 2, and about 420 GtCO 2 for a two-in-three (66%) chance

medium

1

train

519

AR6_WGI

205

22

Using GMST instead of GSAT gives estimates of 770 GtCO 2 and 570 GtCO 2, respectively

medium

1

train

520

AR6_WGI

209

1

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

521

AR6_WGI

209

11

Combining these different sources of evidence, we assess that from the period around 1750 to 1850–1900 there was a change in global temperature of around 0.1 [–0.1 to +0.3] °C (medium confidence), with an anthropogenic component in a likely range of 0.0°C–0.2°C

medium

1

train

522

AR6_WGI

212

15

Overall, tropical regions show earlier emergence of temperature changes than at higher latitudes

high

2

train

523

AR6_WGI

227

7

In summary, the observational coverage of ongoing changes to the climate system is improved at the time of AR6, relative to what was available for AR5

high

2

train

524

AR6_WGI

228

2

Overall, the number, temporal resolution and chronological accuracy of paleoclimate reconstructions have increased since AR5, leading to improved understanding of climate system processes (or Earth system processes)

high

2

train

525

AR6_WGI

228

28

In summary, while the quantity, quality and diversity of climate system observations have grown since AR5, the loss or potential loss of several critical components of the observational network is also evident

high

2

train

526

AR6_WGI

230

6

In summary, the improvements in atmospheric reanalyses, and the greater number of years since the routine ingestion of satellite data began, relative to AR5, mean that there is increased confidence in using atmospheric reanalysis products alongside more standard observation-based datasets in AR6

high

2

train

527

AR6_WGI

231

10

In summary, reanalyses have improved since AR5 and can increasingly be used as a line of evidence in assessments of the state and evolution of the climate system

high

2

train

528

AR6_WGI

239

1

Overall, we assess that increases in computing power and the broader availability of larger and more varied ensembles of model simulations have contributed to better estimations of uncertainty in projections of future change

high

2

train

529

AR6_WGI

297

25

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

2

train

530

AR6_WGI

298

24

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

2

train

531

AR6_WGI

298

26

The average rate of sea level rise was 1.3 [0.6 to 2.1] mm yr–1 between 1901 and 1971, increasing to 1.9 [0.8 to 2.9] mm yr–1 between 1971 and 2006, and further increasing to 3.7 [3.2 to 4.2] mm yr–1 between 2006 and 2018

high

2

train

532

AR6_WGI

299

1

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

2

train

533

AR6_WGI

299

5

The observed average rate of heating of the climate system increased from 0.50 [0.32 to 0.69] W m–2 for the period 1971–2006 to 0.79 [0.52 to 1.06] W m–2 for the period 2006– 2018

high

2

train

534

AR6_WGI

299

6

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

2

train

535

AR6_WGI

299

10

The ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide, causing ocean acidification.In 2019, atmospheric CO 2 concentrations were higher than at any time in at least 2 million years (high confidence), and concentrations of CH 4 and N 2O were higher than at any time in at least 800,000 years

very high

3

train

536

AR6_WGI

299

11

Since 1750, increases in CO 2 (47%) and CH 4 (156%) concentrations far exceed – and increases in N 2O (23%) are similar to – the natural multi-millennial changes between glacial and interglacial periods over at least the past 800,000 years

very high

3

train

537

AR6_WGI

300

11

In the Northern Hemisphere, 1983–2012 was likely the warmest 30-year period of the last 1400 years

medium

1

train

538

AR6_WGI

300

12

Global surface temperature has increased faster since 1970 than in any other 50-year period over at least the last 2000 years

high

2

train

539

AR6_WGI

300

13

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

1

train

540

AR6_WGI

300

14

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

1

train

541

AR6_WGI

300

16

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

2

train

542

AR6_WGI

300

17

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

1

train

543

AR6_WGI

300

18

A long- term increase in surface open ocean pH occurred over the past 50 million years

high

2

train

544

AR6_WGI

300

19

However, surface open ocean pH as low as recent decades is unusual in the last 2 million years

medium

1

train

545

AR6_WGI

302

4

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

1

train

546

AR6_WGI

302

5

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

0

train

547

AR6_WGI

306

9

Present-day global concentrations of atmospheric carbon dioxide (CO 2) are at higher levels than at any time in at least the past two million years

high

2

train

548

AR6_WGI

306

10

Changes in ERF since the late 19th century are dominated by increases in concentrations of greenhouse gases and trends in aerosols; the net ERF is positive and changing at an increasing rate since the 1970s

medium

1

test

549

AR6_WGI

306

12

Solar activity since 1900 was high but not exceptional compared to the past 9000 years

high

2

train

550

AR6_WGI

306

13

The average magnitude and variability of volcanic aerosol forcing since 1900 have not been unusual compared to the past 2500 years

medium

1

train

551

AR6_WGI

306

17

These changes are larger than those between glacial and interglacial periods over the last 800,000 years for CO 2 and CH 4 and of comparable magnitude for N 2O

very high

3

train

552

AR6_WGI

306

21

Aerosol optical depth (AOD) has decreased since 2000 over Northern Hemisphere mid-latitudes and Southern Hemisphere mid-latitude continents, but increased over South Asia and East Africa

high

2

train

553

AR6_WGI

306

25

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

high

2

train

554

AR6_WGI

306

26

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

medium

1

train

555

AR6_WGI

306

27

Since the mid-1990s, free tropospheric ozone increases were 2–7% per decade in the northern mid-latitudes (high confidence), 2–12% per decade in the tropics (high confidence) and <5% per decade in southern mid-latitudes

medium

1

train

556

AR6_WGI

306

31

The best-estimate ERF from the increase in global albedo is –0.15 W m–2 since 1700 and –0.12 W m–2 since 1850

medium

1

test

557

AR6_WGI

306

33

Over the past several decades, key indicators of the climate system are increasingly at levels unseen in centuries to millennia, and are changing at rates unprecedented in at least the last 2000 years

high

2

train

558

AR6_WGI

306

34

Temperatures as high as during the most recent decade (2011–2020) exceed the warmest centennial-scale range reconstructed for the present interglacial, around 6,500 years ago [0.2°C–1°C relative to 1850–1900]

medium

1

train

559

AR6_WGI

306

35

The next older warm period is the last interglacial when the multi-centennial temperature range about 125,000 years ago [0.5°C–1.5°C relative to 1850–1900] encompassed the recent decade values

medium

1

train

560

AR6_WGI

306

40

Over the last 50 years, observed GMST has increased at a rate unprecedented in at least the last 2000 years

high

2

train

561

AR6_WGI

307

4

In the Tropics, the upper troposphere has warmed faster than the near-surface since at least 2001, the period over which new observational techniques permit more robust quantification

medium

1

train

562

AR6_WGI

307

8

Global land precipitation has likely increased since 1950, with a faster increase since the 1980s

medium

1

train

563

AR6_WGI

307

15

Global monsoon precipitation has likely increased since the 1980s, mainly in the Northern Hemisphere

medium

1

train

564

AR6_WGI

307

20

Between 1979 and 2019, Arctic sea ice area has decreased in both summer and winter, with sea ice becoming younger, thinner and more dynamic

very high

3

train

565

AR6_WGI

307

22

Antarctic sea ice area has experienced little net change since 1979

high

2

train

566

AR6_WGI

307

24

Reductions in spring snow cover extent have occurred across the Northern Hemisphere since at least 1978

very high

3

train

567

AR6_WGI

307

25

With few exceptions, glaciers have retreated since the second half of the 19th century and have continued to retreat at increased rates since the 1990s (very high confidence); this behaviour is unprecedented in at least the last 2000 years

medium

1

train

568

AR6_WGI

307

26

Greenland Ice Sheet (GrIS) mass loss has increased substantially since 2000

high

2

train

569

AR6_WGI

307

27

The Greenland Ice Sheet was smaller than at present during the Last Interglacial period (high confidence) and the mid-Holocene

high

2

train

570

AR6_WGI

307

28

The Antarctic Ice Sheet (AIS) lost mass between 1992 and 2020 (very high confidence), with an increasing rate of mass loss over this period

medium

1

train

571

AR6_WGI

307

29

Although permafrost persists in areas of the Northern Hemisphere where it was absent prior to 3000 years ago, increases in temperatures in the upper 30 m over the past three to four decades have been widespread

high

2

train

572

AR6_WGI

307

32

The average rate of sea level rise was 1.3 [0.6 to 2.1] mm yr –1 between 1901 and 1971, increasing to 1.9 [0.8 to 2.9] mm yr –1 between 1971 and 2006, and further increasing to 3.7 [3.2 to 4.2] mm yr –1 between 2006 and 2018

high

2

test

573

AR6_WGI

307

35

Since 1971, it is virtually certain that global ocean heat content has increased for the upper (0–700 m) layer, very likely for the intermediate (700–2000 m) layer and likely below 2000 m, and is currently increasing faster than at any point since at least the last deglacial transition (18 to 11 thousand years ago)

medium

1

train

574

AR6_WGI

307

37

The Atlantic Meridional Overturning Circulation (AMOC) was relatively stable during the past 8000 years (medium confidence) but declined during the 20th century

low

0

train

575

AR6_WGI

307

38

Ocean pH has declined globally at the surface over the past four decades (virtually certain) and in all ocean basins in the ocean interior

high

2

train

576

AR6_WGI

307

39

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

577

AR6_WGI

308

1

Oxygen minimum zones are expanding at many locations

high

2

train

578

AR6_WGI

308

3

The ranges of many marine organisms are shifting towards the poles and towards greater depths

high

2

train

579

AR6_WGI

308

4

This mismatch in responses across species means that the species composition of ecosystems is changing

medium

1

train

580

AR6_WGI

308

5

At multiple locations, various phenological metrics for marine organisms have changed in the last 50 years, with the nature of the changes varying with location and with species

high

2

train

581

AR6_WGI

308

6

In the last two decades, the concentration of phytoplankton at the base of the marine food web, as indexed by chlorophyll concentration, has shown weak and variable trends in low and mid-latitudes and an increase in high latitudes

medium

1

train

582

AR6_WGI

308

7

Global marine primary production decreased slightly from 1998–2018, with increasing production in the Arctic

medium

1

train

583

AR6_WGI

308

9

Over the last century, there have been increases in species turnover within many ecosystems

high

2

test

584

AR6_WGI

308

10

Over the past half century, climate zones have shifted poleward, accompanied by an increase in the length of the growing season in the Northern Hemisphere extratropics and an increase in the amplitude of the seasonal cycle of atmospheric CO 2 above 45°N

high

2

train

585

AR6_WGI

308

11

Since the early 1980s, there has been a global-scale increase in the greenness of the terrestrial surface

high

2

train

586

AR6_WGI

308

13

CO2 levels during the MPWP were similar to present for a sustained period, within a range of 360–420 ppm

medium

1

test

587

AR6_WGI

308

14

Relative to the present, GMST, GMSL and precipitation rate were all higher, the Northern Hemisphere latitudinal temperature gradient was lower, and major terrestrial biomes were shifted northward

very high

3

train

588

AR6_WGI

308

22

Both polar annular modes have exhibited strong positive trends toward increased zonality of mid-latitude circulation over multi-decadal periods, but these trends have not been sustained for the Northern Annular Mode since the early 1990s

high

2

train

589

AR6_WGI

308

23

For tropical ocean modes, a sustained shift beyond multi-centennial variability has not been observed for El Niño–Southern Oscillation

medium

1

train

590

AR6_WGI

308

24

Modes of decadal and multi-decadal variability over the Pacific and Atlantic oceans exhibit no significant trends over the period of observational records

high

2

train

591

AR6_WGI

314

1

To conclude, solar activity since the late 19th century was relatively high but not exceptional in the context of the past 9 kyr

high

2

train

592

AR6_WGI

314

25

However, the average magnitude and variability of SAOD and its associated volcanic aerosol forcing since 1900 are not unusual in the context of at least the past 2.5 kyr

medium

1

train

593

AR6_WGI

315

13

Based on boron and carbon isotope data, supported by other proxies (Hollis et al., 2019), atmospheric CO2 during the EECO (50 Ma) was between 1150 and 2500 ppm

medium

1

test

594

AR6_WGI

316

6

High-resolution sampling (about 1 sample per 3 kyr) with the boron-isotope proxy indicates mean CO 2 mixing ratios for the Marine Isotope Stage KM5c interglacial were 360–420 ppm

medium

1

train

595

AR6_WGI

316

21

Although ice core records present low-pass filtered time series due to gas diffusion and gradual bubble close- off in the snow layer over the ice sheet (Fourteau et al., 2020), the rate of increase since 1850 CE (about 125 ppm increase over about 170 years) is far greater than implied for any 170-year period by ice core records that cover the last 800 ka

very high

3

train

596

AR6_WGI

319

15

The last time CO 2 concentrations were similar to the present-day was over 2 Ma

high

2

train

597

AR6_WGI

319

18

Between 1750–2019 mixing ratios increased by 131.6 ± 2.9 ppm (47%), 1137 ± 10 ppb (156%), and 62 ± 6 ppb (23%), for CO 2, CH 4, and N 2O, respectively

very high

3

train

598

AR6_WGI

323

29

In summary, limited available isotopic evidence constrains the global tropospheric ozone increase to less than 40% between 1850 and 2005

low

0

train

599

AR6_WGI

323

30

Based on sparse historical surface/low altitude data tropospheric ozone has increased since the mid-20th century by 30–70% across the NH

medium

1

train