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
700	AR6_WGI	390	7	Neither the IOD nor the IOB have exhibited behaviour outside the range implied by proxy records	low	0	train
701	AR6_WGI	392	12	In summary, no sustained change in AMV indices has been observed over the instrumental period	high	2	train
702	AR6_WGI	441	11	High-resolution models exhibit reduced biases in some but not all aspects of surface and ocean climate (medium confidence), and most Earth system models, which include biogeochemical feedbacks, perform as well as their lower-complexity counterparts	medium	1	train
703	AR6_WGI	441	12	The multi-model mean captures most aspects of observed climate change well	high	2	train
704	AR6_WGI	441	13	The multi-model mean captures the proxy-reconstructed global-mean surface air temperature (GSAT) change during past high- and low-CO 2 climates (high confidence) and the correct sign of temperature and precipitation change in most assessed regions in the mid-Holocene	medium	1	train
705	AR6_WGI	441	14	The simulation of paleoclimates on continental scales has improved compared to AR5 (medium confidence), but models often underestimate large temperature and precipitation differences relative to the present day	high	2	train
706	AR6_WGI	441	19	The likely ranges for human-induced GSAT and global mean surface temperature (GMST) warming are equal	medium	1	train
707	AR6_WGI	441	26	CMIP6 models broadly reproduce surface temperature variations over the past millennium, including the cooling that follows periods of intense volcanism	medium	1	train
708	AR6_WGI	441	28	The latest updates to satellite-derived estimates of stratospheric temperature have resulted in decreased differences between simulated and observed changes of global mean temperature through the depth of the stratosphere	medium	1	train
709	AR6_WGI	441	31	All the observed estimates of the 1998–2012 GMST trend lie within the 10th–90th percentile range of CMIP6 simulated trends	high	2	train
710	AR6_WGI	441	32	Internal variability, particularly Pacific Decadal Variability, and variations in solar and volcanic forcings partly offset the anthropogenic surface warming trend over the 1998–2012 period	high	2	train
711	AR6_WGI	442	1	Since 2012, GMST has warmed strongly, with the past five years (2016–2020) being the warmest five-year period in the instrumental record since at least 1850	high	2	train
712	AR6_WGI	442	5	New attribution studies strengthen previous findings of a detectable increase in Northern Hemisphere mid- to high-latitude land precipitation	high	2	train
713	AR6_WGI	442	6	Human influence has contributed to strengthening the zonal mean precipitation contrast between the wet tropics and dry subtropics	medium	1	train
714	AR6_WGI	442	7	Yet, anthropogenic aerosols contributed to decreasing global land summer monsoon precipitation from the 1950s to 1980s	medium	1	train
715	AR6_WGI	442	9	Despite improvements, models still have deficiencies in simulating precipitation patterns, particularly over the tropical ocean	high	2	train
716	AR6_WGI	442	13	The magnitude and frequency of extreme precipitation simulated by CMIP6 models are similar to those simulated by CMIP5 models	high	2	train
717	AR6_WGI	442	16	The causes of the observed strengthening of the Pacific Walker circulation since the 1980s are not well understood, and the observed strengthening trend is outside the range of trends simulated in the coupled models	medium	1	train
718	AR6_WGI	442	17	While CMIP6 models capture the general characteristics of the tropospheric large-scale circulation (high confidence), systematic biases exist in the mean frequency of atmospheric blocking events, especially in the Euro-Atlantic sector, some of which reduce with increasing model resolution	medium	1	train
719	AR6_WGI	442	19	There is new evidence that increases in anthropogenic aerosols have offset part of the greenhouse gas-induced Arctic sea ice loss since the 1950s	medium	1	train
720	AR6_WGI	442	20	In the Arctic, despite large differences in the mean sea ice state, loss of sea ice extent and thickness during recent decades is reproduced in all CMIP5 and CMIP6 models	high	2	train
721	AR6_WGI	442	23	The seasonal cycle in Northern Hemisphere snow cover is better reproduced by CMIP6 than by CMIP5 models	high	2	train
722	AR6_WGI	442	29	Updated observations and model simulations show that warming extends throughout the entire water column	high	2	train
723	AR6_WGI	442	30	The structure and magnitude of multi-model mean ocean temperature biases have not changed substantially between CMIP5 and CMIP6	medium	1	train
724	AR6_WGI	442	32	The associated pattern of change corresponds to fresh regions becoming fresher and salty regions becoming saltier	high	2	train
725	AR6_WGI	442	33	Changes to the coincident atmospheric water cycle and ocean-atmosphere fluxes (evaporation and precipitation) are the primary drivers of the observed basin-scale salinity changes	high	2	train
726	AR6_WGI	443	1	The basin-scale changes are consistent across models and intensify through the historical period	high	2	train
727	AR6_WGI	443	2	The structure of the biases in the multi-model mean has not changed substantially between CMIP5 and CMIP6	medium	1	train
728	AR6_WGI	443	9	However, biases are apparent in the modelled circulation strengths (high confidence) and their variability	medium	1	train
729	AR6_WGI	443	12	Earth system models simulate globally averaged land carbon sinks within the range of observation-based estimates	high	2	train
730	AR6_WGI	443	18	The influence of ozone forcing on the SAM trend has been small since the early 2000s compared to earlier decades, contributing to a weaker SAM trend observed over 2000–2019	medium	1	train
731	AR6_WGI	443	19	Climate models reproduce the summertime SAM trend well, with CMIP6 models outperforming CMIP5 models	medium	1	train
732	AR6_WGI	443	21	Models reproduce the observed spatial features and variance of the SAM and NAM very well	high	2	train
733	AR6_WGI	443	23	Further assessment since AR5 confirms that climate and Earth system models are able to reproduce most aspects of the spatial structure and variance of the El Niño–Southern Oscillation and Indian Ocean Basin and Dipole modes	medium	1	train
734	AR6_WGI	443	28	Uncertainties remain in quantification of the human influence on AMV and PDV due to brevity of the observational records, limited model performance in reproducing related sea surface temperature (SST) anomalies despite improvements from CMIP5 to CMIP6	medium	1	train
735	AR6_WGI	449	6	CMIP6 models broadly reproduce surface temperature variations over the past millennium, including the cooling that follows periods of intense volcanism	medium	1	train
736	AR6_WGI	449	7	Simulated GMST anomalies are well within the uncertainty range of temperature reconstructions	medium	1	test
737	AR6_WGI	449	8	Before the year 1300, larger disagreements between models and temperature reconstructions are expected because forcing and temperature reconstructions are increasingly uncertain further back in time, but specific causes have not been identified conclusively (Ljungqvist et al., 2019; PAGES 2k Consortium, 2019)	medium	1	train
738	AR6_WGI	454	18	CMIP6 models also reproduce historical GSAT changes similarly to their CMIP5 counterparts	medium	1	train
739	AR6_WGI	461	26	In summary, based on the latest updates to satellite observations of stratospheric temperature, we assess that simulated and observed trends in global mean temperature through the depth of the stratosphere are more consistent than based on previous datasets, but some differences remain	medium	1	train
740	AR6_WGI	462	13	Therefore, the observed 1998–2012 trend is consistent with both the CMIP5 or CMIP6 multi-model ensemble of trends over the same period	high	2	train
741	AR6_WGI	463	12	Although there is noticeable uncertainty among observational products (H. Su et al., 2017) and observation quality changes through time, global ocean heat content continued to increase during the slower surface warming period	very high	3	test
742	AR6_WGI	463	20	Nonetheless, 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
743	AR6_WGI	463	23	The past five-year period (2016–2020) is the hottest five-year period in the instrumental record up to 2020	high	2	train
744	AR6_WGI	465	7	Records of tree ring width have provided evidence that recent prolonged dry spells in the Levant and Chile are unprecedented in the last millennium	high	2	train
745	AR6_WGI	465	10	Likewise, tree rings indicate that the 2012–2014 drought in the south-western United States was exceptionally severe in the context of natural variability over the last millennium, and may have been exacerbated by the contribution of anthropogenic temperature rise	medium	1	train
746	AR6_WGI	465	13	Nonetheless, tree rings also indicate the presence of prolonged megadroughts in western North America throughout the last millennium that were more severe than 20th and 21st century events	high	2	train
747	AR6_WGI	466	4	However, prescribing changes in vegetation and dust was found to improve the match to the paleoclimate record (Pausata et al., 2016; Tierney et al., 2017) suggesting that vegetation feedbacks in the CMIP5 models may be too weak	low	0	train
748	AR6_WGI	468	30	Based on these results we assess that despite some improvements, CMIP6 models still have deficiencies in simulating precipitation patterns, particularly over the tropical ocean	high	2	train
749	AR6_WGI	470	11	Global land precipitation has likely increased since the middle of the 20th century	medium	1	train
750	AR6_WGI	472	11	New attribution studies strengthen previous findings of a detectable increase in mid to high latitude land precipitation over the Northern Hemisphere	high	2	train
751	AR6_WGI	472	36	Moreover, human interventions and water withdrawals, while affecting streamflow, cannot explain the observed spatio-temporal trends	medium	1	train
752	AR6_WGI	473	17	The overall performance of CMIP6 models in simulating extreme precipitation intensity and frequency is similar to that of CMIP5 models	high	2	train
753	AR6_WGI	477	9	For the strong ozone depletion period of 1981–2000, human influence is detectable in the summertime poleward expansion in the Southern Hemisphere	medium	1	train
754	AR6_WGI	477	11	The causes of the observed strengthening of the Pacific Walker circulation over the 1980–2014 period are not well understood, since the observed strengthening trend is outside the range of variability simulated in the coupled models	medium	1	train
755	AR6_WGI	477	18	AR5 assessed that CMIP5 models simulated monsoons better than CMIP3 models but that biases remained in domains and intensity	high	2	train
756	AR6_WGI	479	15	In summary, while greenhouse gas increases acted to enhance the global land monsoon precipitation over the 20th century (medium confidence), consistent with projected future enhancement (Section 4.5.1.5), this tendency was overwhelmed by anthropogenic aerosols from the 1950s to the 1980s, which contributed to weakening of global land summer monsoon precipitation intensity for this period	medium	1	train
757	AR6_WGI	479	19	While CMIP5 models can capture the domain and precipitation intensity of the global monsoon, biases remain in their regional representations, and they are unsuccessful in quantitatively reproducing changes in paleo reconstructions	high	2	train
758	AR6_WGI	479	20	CMIP6 models reproduce the domain and precipitation intensity of the global monsoon observed over the instrumental period better than CMIP5 models	medium	1	train
759	AR6_WGI	480	23	Section 2.3.1.4.3 assesses that the total number of extratropical cyclones has likely increased since the 1980s in the Northern Hemisphere	low	0	train
760	AR6_WGI	480	28	Section 2.3.1.4.3 assesses that the extratropical jets and cyclone tracks have likely shifted poleward in both hemispheres since the 1980s with marked seasonality in trends	medium	1	train
761	AR6_WGI	482	22	The recent Arctic sea ice loss during summer is unprecedented since 1850	high	2	train
762	AR6_WGI	483	10	Sea ice thermodynamic considerations indicate that the magnitude of sea ice variability and loss depends on ice thickness (Bitz, 2008; Massonnet et al., 2018) and hence the climatology simulated by different models may influence their simulated sea ice trends	medium	1	train
763	AR6_WGI	483	11	An important consideration in comparing Arctic sea ice loss in models and observations is the role of internal variability	medium	1	train
764	AR6_WGI	484	12	Increases in anthropogenic aerosols have offset part of the greenhouse gas induced Arctic sea ice loss since the 1950s	medium	1	train
765	AR6_WGI	487	6	CMIP6 models better represent the seasonality and geographical distribution of snow cover than CMIP5 simulations	high	2	train
766	AR6_WGI	488	9	Section 2.3.2.4.1 assesses that Greenland Ice Sheet mass loss began in the latter half of the 19th century and that the rate of loss has increased substantially since the turn of the 21st century	high	2	train
767	AR6_WGI	488	25	It further assessed that Antarctic ice loss is dominated by acceleration, retreat and rapid thinning of the major West Antarctic Ice Sheet outlet glaciers (very high confidence), driven by melting of ice shelves by warm ocean waters	high	2	train
768	AR6_WGI	492	1	Nevertheless, the CMIP6 models show a somewhat more realistic pattern of SST trends	low	0	test
769	AR6_WGI	493	6	The multi-model means of both CMIP5 and CMIP6 historical simulations forced with time varying natural and anthropogenic forcing shows robust increases in ocean heat content in the upper (0–700 m) and intermediate (700–2000 m) ocean	high	2	train
770	AR6_WGI	494	14	It is extremely likely that human influence was the main driver of the ocean heat content increase observed since the 1970s, which extends into the deeper ocean	very high	3	train
771	AR6_WGI	494	15	Updated observations, like model simulations, show that warming extends throughout the entire water column	high	2	train
772	AR6_WGI	495	14	The structure of the salinity biases in the multi-model mean has not changed substantially between CMIP5 and CMIP6	medium	1	test
773	AR6_WGI	497	5	All available multi-decadal assessments have confirmed that the associated pattern of change corresponds to fresh regions becoming fresher and salty regions becoming saltier	high	2	train
774	AR6_WGI	497	6	CMIP5 and CMIP6 models are only able to reproduce these patterns in simulations that include greenhouse gas increases	medium	1	test
775	AR6_WGI	497	7	Changes to the coincident atmospheric water cycle and ocean-atmosphere fluxes (evaporation and precipitation) are the primary drivers of the basin-scale observed salinity changes	high	2	train
776	AR6_WGI	497	9	The basin-scale changes are consistent across models and intensify on centennial scales from the historical period through to the projections of future climate	high	2	train
777	AR6_WGI	499	27	As reported in Section 2.3.3.4.1, estimates of AMOC since at least 1950, which are generated from observed surface temperatures or sea surface height, suggest the AMOC weakened through the 20th century	low	0	train
778	AR6_WGI	501	21	In summary, while there have been improvements across successive CMIP phases (from CMIP3 to CMIP6) in the representation of the Southern Ocean circulation, such that the mean zonal and overturning circulations of the Southern Ocean are now broadly reproduced, substantial observational uncertainty and climate model challenges preclude attribution of Southern Ocean circulation changes	high	2	train
779	AR6_WGI	501	24	That increase was attributed to direct land use and management changes, as well as to CO 2 fertilization, nitrogen deposition, increased diffuse radiation and climate change	high	2	train
780	AR6_WGI	503	40	In summary, Earth system models simulate globally averaged land carbon sinks within the range of observation-based estimates	high	2	train
781	AR6_WGI	504	15	The decrease in ocean oxygen content in the upper 1000 m, between 1970 and 2010, is further confirmed in SROCC	medium	1	train
782	AR6_WGI	505	6	Section 5.2.1.3 assesses that both observational reconstructions based on the partial pressure of CO 2 and ocean biogeochemical models show a quasi-linear increase in the ocean sink of anthropogenic CO 2 from 1.0 ± 0.3 PgC yr–1 to 2.5 ± 0.6 PgC yr–1 between 1960–1969 and 2010–2019 in response to global CO 2 emissions	high	2	train
783	AR6_WGI	509	9	CMIP5 and CMIP6 models are skilful in simulating the spatial features and the variance of the NAM/NAO and associated teleconnections	high	2	test
784	AR6_WGI	510	20	However, despite the aforementioned limitations of the reconstructions, Section 2.4.1.2 assesses that the recent positive trend in the SAM is likely unprecedented in at least the past millennium	medium	1	train
785	AR6_WGI	510	24	While ozone depletion contributed to the trend from the 1970s to the 1990s (medium confidence), its influence has been small since 2000, leading to a weaker summertime SAM trend over 2000–2019	medium	1	train
786	AR6_WGI	510	25	Climate models reproduce the spatial structure of the summertime SAM observed since the late 1970s well	high	2	train
787	AR6_WGI	510	26	CMIP6 models reproduce the spatiotemporal features and recent multi-decadal trend of the summertime SAM better than CMIP5 models	medium	1	train
788	AR6_WGI	510	27	However, there is a large spread in the intensity of the SAM response to ozone and greenhouse gas changes in both CMIP5 and CMIP6 models	high	2	train
789	AR6_WGI	511	1	CMIP5 and CMIP6 models do not capture multicentennial variability of the SAM found in proxy reconstructions	low	0	train
790	AR6_WGI	511	16	As assessed in Section 2.4.2, ENSO amplitude since 1950 is higher than over the pre-industrial period from 1850 as far back as 1400	medium	1	train
791	AR6_WGI	517	1	Nevertheless, CMIP5 models have medium overall performance in reproducing both the interannual IOB and IOD modes, with an apparently good performance in reproducing the IOB magnitude arising from compensation of biases in the formation process, and overly high IOD magnitude due to the mean state bias	high	2	train
792	AR6_WGI	520	3	As such, PDV is an important driver of decadal internal climate variability which limits detection of human influence on various aspects of decadal climate change on global to regional scales	high	2	train
793	AR6_WGI	520	5	Despite the limitations of these model-observation comparisons, CMIP5 models, on average, simulate broadly realistic spatial structures of the PDV, but with a clear bias in the South Pacific	medium	1	train
794	AR6_WGI	522	5	In particular, anthropogenic and volcanic aerosols are thought to have played a role in the timing and intensity of the negative (cold) phase of AMV recorded from the mid-1960s to mid-1990s and subsequent warming	medium	1	train
795	AR6_WGI	522	23	The pattern of ocean salinity changes indicate that fresh regions are becoming fresher and that salty regions are becoming saltier as a result of changes in ocean-atmosphere fluxes through evaporation and precipitation	high	2	test
796	AR6_WGI	526	1	Earth System models characterized by additional biogeochemical feedbacks often perform at least as well as related more constrained, lower-complexity models lacking these feedbacks	medium	1	train
797	AR6_WGI	526	2	In many cases, the models score similarly against both observational references, indicating that model errors are usually larger than observational uncertainties	high	2	train
798	AR6_WGI	526	3	Moreover, synthesizing across Sections 3.3–3.7, we assess that the CMIP6 multi-model mean captures most aspects of observed climate change well	high	2	train
799	AR6_WGI	528	27	Overall, the PMIP multi-model means agree very well (within 0.5°C of the assessed range) with GSAT reconstructed from proxies across multiple time periods, spanning a range from 6°C colder than pre-industrial (Last Glacial Maximum) to 14°C warmer than pre-industrial (Early Eocene Climate Optimum)	high	2	train

700

AR6_WGI

390

7

Neither the IOD nor the IOB have exhibited behaviour outside the range implied by proxy records

low

0

train

701

AR6_WGI

392

12

In summary, no sustained change in AMV indices has been observed over the instrumental period

high

2

train

702

AR6_WGI

441

11

High-resolution models exhibit reduced biases in some but not all aspects of surface and ocean climate (medium confidence), and most Earth system models, which include biogeochemical feedbacks, perform as well as their lower-complexity counterparts

medium

1

train

703

AR6_WGI

441

12

The multi-model mean captures most aspects of observed climate change well

high

2

train

704

AR6_WGI

441

13

The multi-model mean captures the proxy-reconstructed global-mean surface air temperature (GSAT) change during past high- and low-CO 2 climates (high confidence) and the correct sign of temperature and precipitation change in most assessed regions in the mid-Holocene

medium

1

train

705

AR6_WGI

441

14

The simulation of paleoclimates on continental scales has improved compared to AR5 (medium confidence), but models often underestimate large temperature and precipitation differences relative to the present day

high

2

train

706

AR6_WGI

441

19

The likely ranges for human-induced GSAT and global mean surface temperature (GMST) warming are equal

medium

1

train

707

AR6_WGI

441

26

CMIP6 models broadly reproduce surface temperature variations over the past millennium, including the cooling that follows periods of intense volcanism

medium

1

train

708

AR6_WGI

441

28

The latest updates to satellite-derived estimates of stratospheric temperature have resulted in decreased differences between simulated and observed changes of global mean temperature through the depth of the stratosphere

medium

1

train

709

AR6_WGI

441

31

All the observed estimates of the 1998–2012 GMST trend lie within the 10th–90th percentile range of CMIP6 simulated trends

high

2

train

710

AR6_WGI

441

32

Internal variability, particularly Pacific Decadal Variability, and variations in solar and volcanic forcings partly offset the anthropogenic surface warming trend over the 1998–2012 period

high

2

train

711

AR6_WGI

442

1

Since 2012, GMST has warmed strongly, with the past five years (2016–2020) being the warmest five-year period in the instrumental record since at least 1850

high

2

train

712

AR6_WGI

442

5

New attribution studies strengthen previous findings of a detectable increase in Northern Hemisphere mid- to high-latitude land precipitation

high

2

train

713

AR6_WGI

442

6

Human influence has contributed to strengthening the zonal mean precipitation contrast between the wet tropics and dry subtropics

medium

1

train

714

AR6_WGI

442

7

Yet, anthropogenic aerosols contributed to decreasing global land summer monsoon precipitation from the 1950s to 1980s

medium

1

train

715

AR6_WGI

442

9

Despite improvements, models still have deficiencies in simulating precipitation patterns, particularly over the tropical ocean

high

2

train

716

AR6_WGI

442

13

The magnitude and frequency of extreme precipitation simulated by CMIP6 models are similar to those simulated by CMIP5 models

high

2

train

717

AR6_WGI

442

16

The causes of the observed strengthening of the Pacific Walker circulation since the 1980s are not well understood, and the observed strengthening trend is outside the range of trends simulated in the coupled models

medium

1

train

718

AR6_WGI

442

17

While CMIP6 models capture the general characteristics of the tropospheric large-scale circulation (high confidence), systematic biases exist in the mean frequency of atmospheric blocking events, especially in the Euro-Atlantic sector, some of which reduce with increasing model resolution

medium

1

train

719

AR6_WGI

442

19

There is new evidence that increases in anthropogenic aerosols have offset part of the greenhouse gas-induced Arctic sea ice loss since the 1950s

medium

1

train

720

AR6_WGI

442

20

In the Arctic, despite large differences in the mean sea ice state, loss of sea ice extent and thickness during recent decades is reproduced in all CMIP5 and CMIP6 models

high

2

train

721

AR6_WGI

442

23

The seasonal cycle in Northern Hemisphere snow cover is better reproduced by CMIP6 than by CMIP5 models

high

2

train

722

AR6_WGI

442

29

Updated observations and model simulations show that warming extends throughout the entire water column

high

2

train

723

AR6_WGI

442

30

The structure and magnitude of multi-model mean ocean temperature biases have not changed substantially between CMIP5 and CMIP6

medium

1

train

724

AR6_WGI

442

32

The associated pattern of change corresponds to fresh regions becoming fresher and salty regions becoming saltier

high

2

train

725

AR6_WGI

442

33

Changes to the coincident atmospheric water cycle and ocean-atmosphere fluxes (evaporation and precipitation) are the primary drivers of the observed basin-scale salinity changes

high

2

train

726

AR6_WGI

443

1

The basin-scale changes are consistent across models and intensify through the historical period

high

2

train

727

AR6_WGI

443

2

The structure of the biases in the multi-model mean has not changed substantially between CMIP5 and CMIP6

medium

1

train

728

AR6_WGI

443

9

However, biases are apparent in the modelled circulation strengths (high confidence) and their variability

medium

1

train

729

AR6_WGI

443

12

Earth system models simulate globally averaged land carbon sinks within the range of observation-based estimates

high

2

train

730

AR6_WGI

443

18

The influence of ozone forcing on the SAM trend has been small since the early 2000s compared to earlier decades, contributing to a weaker SAM trend observed over 2000–2019

medium

1

train

731

AR6_WGI

443

19

Climate models reproduce the summertime SAM trend well, with CMIP6 models outperforming CMIP5 models

medium

1

train

732

AR6_WGI

443

21

Models reproduce the observed spatial features and variance of the SAM and NAM very well

high

2

train

733

AR6_WGI

443

23

Further assessment since AR5 confirms that climate and Earth system models are able to reproduce most aspects of the spatial structure and variance of the El Niño–Southern Oscillation and Indian Ocean Basin and Dipole modes

medium

1

train

734

AR6_WGI

443

28

Uncertainties remain in quantification of the human influence on AMV and PDV due to brevity of the observational records, limited model performance in reproducing related sea surface temperature (SST) anomalies despite improvements from CMIP5 to CMIP6

medium

1

train

735

AR6_WGI

449

6

CMIP6 models broadly reproduce surface temperature variations over the past millennium, including the cooling that follows periods of intense volcanism

medium

1

train

736

AR6_WGI

449

7

Simulated GMST anomalies are well within the uncertainty range of temperature reconstructions

medium

1

test

737

AR6_WGI

449

8

Before the year 1300, larger disagreements between models and temperature reconstructions are expected because forcing and temperature reconstructions are increasingly uncertain further back in time, but specific causes have not been identified conclusively (Ljungqvist et al., 2019; PAGES 2k Consortium, 2019)

medium

1

train

738

AR6_WGI

454

18

CMIP6 models also reproduce historical GSAT changes similarly to their CMIP5 counterparts

medium

1

train

739

AR6_WGI

461

26

In summary, based on the latest updates to satellite observations of stratospheric temperature, we assess that simulated and observed trends in global mean temperature through the depth of the stratosphere are more consistent than based on previous datasets, but some differences remain

medium

1

train

740

AR6_WGI

462

13

Therefore, the observed 1998–2012 trend is consistent with both the CMIP5 or CMIP6 multi-model ensemble of trends over the same period

high

2

train

741

AR6_WGI

463

12

Although there is noticeable uncertainty among observational products (H. Su et al., 2017) and observation quality changes through time, global ocean heat content continued to increase during the slower surface warming period

very high

3

test

742

AR6_WGI

463

20

Nonetheless, 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

743

AR6_WGI

463

23

The past five-year period (2016–2020) is the hottest five-year period in the instrumental record up to 2020

high

2

train

744

AR6_WGI

465

7

Records of tree ring width have provided evidence that recent prolonged dry spells in the Levant and Chile are unprecedented in the last millennium

high

2

train

745

AR6_WGI

465

10

Likewise, tree rings indicate that the 2012–2014 drought in the south-western United States was exceptionally severe in the context of natural variability over the last millennium, and may have been exacerbated by the contribution of anthropogenic temperature rise

medium

1

train

746

AR6_WGI

465

13

Nonetheless, tree rings also indicate the presence of prolonged megadroughts in western North America throughout the last millennium that were more severe than 20th and 21st century events

high

2

train

747

AR6_WGI

466

4

However, prescribing changes in vegetation and dust was found to improve the match to the paleoclimate record (Pausata et al., 2016; Tierney et al., 2017) suggesting that vegetation feedbacks in the CMIP5 models may be too weak

low

0

train

748

AR6_WGI

468

30

Based on these results we assess that despite some improvements, CMIP6 models still have deficiencies in simulating precipitation patterns, particularly over the tropical ocean

high

2

train

749

AR6_WGI

470

11

Global land precipitation has likely increased since the middle of the 20th century

medium

1

train

750

AR6_WGI

472

11

New attribution studies strengthen previous findings of a detectable increase in mid to high latitude land precipitation over the Northern Hemisphere

high

2

train

751

AR6_WGI

472

36

Moreover, human interventions and water withdrawals, while affecting streamflow, cannot explain the observed spatio-temporal trends

medium

1

train

752

AR6_WGI

473

17

The overall performance of CMIP6 models in simulating extreme precipitation intensity and frequency is similar to that of CMIP5 models

high

2

train

753

AR6_WGI

477

9

For the strong ozone depletion period of 1981–2000, human influence is detectable in the summertime poleward expansion in the Southern Hemisphere

medium

1

train

754

AR6_WGI

477

11

The causes of the observed strengthening of the Pacific Walker circulation over the 1980–2014 period are not well understood, since the observed strengthening trend is outside the range of variability simulated in the coupled models

medium

1

train

755

AR6_WGI

477

18

AR5 assessed that CMIP5 models simulated monsoons better than CMIP3 models but that biases remained in domains and intensity

high

2

train

756

AR6_WGI

479

15

In summary, while greenhouse gas increases acted to enhance the global land monsoon precipitation over the 20th century (medium confidence), consistent with projected future enhancement (Section 4.5.1.5), this tendency was overwhelmed by anthropogenic aerosols from the 1950s to the 1980s, which contributed to weakening of global land summer monsoon precipitation intensity for this period

medium

1

train

757

AR6_WGI

479

19

While CMIP5 models can capture the domain and precipitation intensity of the global monsoon, biases remain in their regional representations, and they are unsuccessful in quantitatively reproducing changes in paleo reconstructions

high

2

train

758

AR6_WGI

479

20

CMIP6 models reproduce the domain and precipitation intensity of the global monsoon observed over the instrumental period better than CMIP5 models

medium

1

train

759

AR6_WGI

480

23

Section 2.3.1.4.3 assesses that the total number of extratropical cyclones has likely increased since the 1980s in the Northern Hemisphere

low

0

train

760

AR6_WGI

480

28

Section 2.3.1.4.3 assesses that the extratropical jets and cyclone tracks have likely shifted poleward in both hemispheres since the 1980s with marked seasonality in trends

medium

1

train

761

AR6_WGI

482

22

The recent Arctic sea ice loss during summer is unprecedented since 1850

high

2

train

762

AR6_WGI

483

10

Sea ice thermodynamic considerations indicate that the magnitude of sea ice variability and loss depends on ice thickness (Bitz, 2008; Massonnet et al., 2018) and hence the climatology simulated by different models may influence their simulated sea ice trends

medium

1

train

763

AR6_WGI

483

11

An important consideration in comparing Arctic sea ice loss in models and observations is the role of internal variability

medium

1

train

764

AR6_WGI

484

12

Increases in anthropogenic aerosols have offset part of the greenhouse gas induced Arctic sea ice loss since the 1950s

medium

1

train

765

AR6_WGI

487

6

CMIP6 models better represent the seasonality and geographical distribution of snow cover than CMIP5 simulations

high

2

train

766

AR6_WGI

488

9

Section 2.3.2.4.1 assesses that Greenland Ice Sheet mass loss began in the latter half of the 19th century and that the rate of loss has increased substantially since the turn of the 21st century

high

2

train

767

AR6_WGI

488

25

It further assessed that Antarctic ice loss is dominated by acceleration, retreat and rapid thinning of the major West Antarctic Ice Sheet outlet glaciers (very high confidence), driven by melting of ice shelves by warm ocean waters

high

2

train

768

AR6_WGI

492

1

Nevertheless, the CMIP6 models show a somewhat more realistic pattern of SST trends

low

0

test

769

AR6_WGI

493

6

The multi-model means of both CMIP5 and CMIP6 historical simulations forced with time varying natural and anthropogenic forcing shows robust increases in ocean heat content in the upper (0–700 m) and intermediate (700–2000 m) ocean

high

2

train

770

AR6_WGI

494

14

It is extremely likely that human influence was the main driver of the ocean heat content increase observed since the 1970s, which extends into the deeper ocean

very high

3

train

771

AR6_WGI

494

15

Updated observations, like model simulations, show that warming extends throughout the entire water column

high

2

train

772

AR6_WGI

495

14

The structure of the salinity biases in the multi-model mean has not changed substantially between CMIP5 and CMIP6

medium

1

test

773

AR6_WGI

497

5

All available multi-decadal assessments have confirmed that the associated pattern of change corresponds to fresh regions becoming fresher and salty regions becoming saltier

high

2

train

774

AR6_WGI

497

6

CMIP5 and CMIP6 models are only able to reproduce these patterns in simulations that include greenhouse gas increases

medium

1

test

775

AR6_WGI

497

7

Changes to the coincident atmospheric water cycle and ocean-atmosphere fluxes (evaporation and precipitation) are the primary drivers of the basin-scale observed salinity changes

high

2

train

776

AR6_WGI

497

9

The basin-scale changes are consistent across models and intensify on centennial scales from the historical period through to the projections of future climate

high

2

train

777

AR6_WGI

499

27

As reported in Section 2.3.3.4.1, estimates of AMOC since at least 1950, which are generated from observed surface temperatures or sea surface height, suggest the AMOC weakened through the 20th century

low

0

train

778

AR6_WGI

501

21

In summary, while there have been improvements across successive CMIP phases (from CMIP3 to CMIP6) in the representation of the Southern Ocean circulation, such that the mean zonal and overturning circulations of the Southern Ocean are now broadly reproduced, substantial observational uncertainty and climate model challenges preclude attribution of Southern Ocean circulation changes

high

2

train

779

AR6_WGI

501

24

That increase was attributed to direct land use and management changes, as well as to CO 2 fertilization, nitrogen deposition, increased diffuse radiation and climate change

high

2

train

780

AR6_WGI

503

40

In summary, Earth system models simulate globally averaged land carbon sinks within the range of observation-based estimates

high

2

train

781

AR6_WGI

504

15

The decrease in ocean oxygen content in the upper 1000 m, between 1970 and 2010, is further confirmed in SROCC

medium

1

train

782

AR6_WGI

505

6

Section 5.2.1.3 assesses that both observational reconstructions based on the partial pressure of CO 2 and ocean biogeochemical models show a quasi-linear increase in the ocean sink of anthropogenic CO 2 from 1.0 ± 0.3 PgC yr–1 to 2.5 ± 0.6 PgC yr–1 between 1960–1969 and 2010–2019 in response to global CO 2 emissions

high

2

train

783

AR6_WGI

509

9

CMIP5 and CMIP6 models are skilful in simulating the spatial features and the variance of the NAM/NAO and associated teleconnections

high

2

test

784

AR6_WGI

510

20

However, despite the aforementioned limitations of the reconstructions, Section 2.4.1.2 assesses that the recent positive trend in the SAM is likely unprecedented in at least the past millennium

medium

1

train

785

AR6_WGI

510

24

While ozone depletion contributed to the trend from the 1970s to the 1990s (medium confidence), its influence has been small since 2000, leading to a weaker summertime SAM trend over 2000–2019

medium

1

train

786

AR6_WGI

510

25

Climate models reproduce the spatial structure of the summertime SAM observed since the late 1970s well

high

2

train

787

AR6_WGI

510

26

CMIP6 models reproduce the spatiotemporal features and recent multi-decadal trend of the summertime SAM better than CMIP5 models

medium

1

train

788

AR6_WGI

510

27

However, there is a large spread in the intensity of the SAM response to ozone and greenhouse gas changes in both CMIP5 and CMIP6 models

high

2

train

789

AR6_WGI

511

1

CMIP5 and CMIP6 models do not capture multicentennial variability of the SAM found in proxy reconstructions

low

0

train

790

AR6_WGI

511

16

As assessed in Section 2.4.2, ENSO amplitude since 1950 is higher than over the pre-industrial period from 1850 as far back as 1400

medium

1

train

791

AR6_WGI

517

1

Nevertheless, CMIP5 models have medium overall performance in reproducing both the interannual IOB and IOD modes, with an apparently good performance in reproducing the IOB magnitude arising from compensation of biases in the formation process, and overly high IOD magnitude due to the mean state bias

high

2

train

792

AR6_WGI

520

3

As such, PDV is an important driver of decadal internal climate variability which limits detection of human influence on various aspects of decadal climate change on global to regional scales

high

2

train

793

AR6_WGI

520

5

Despite the limitations of these model-observation comparisons, CMIP5 models, on average, simulate broadly realistic spatial structures of the PDV, but with a clear bias in the South Pacific

medium

1

train

794

AR6_WGI

522

5

In particular, anthropogenic and volcanic aerosols are thought to have played a role in the timing and intensity of the negative (cold) phase of AMV recorded from the mid-1960s to mid-1990s and subsequent warming

medium

1

train

795

AR6_WGI

522

23

The pattern of ocean salinity changes indicate that fresh regions are becoming fresher and that salty regions are becoming saltier as a result of changes in ocean-atmosphere fluxes through evaporation and precipitation

high

2

test

796

AR6_WGI

526

1

Earth System models characterized by additional biogeochemical feedbacks often perform at least as well as related more constrained, lower-complexity models lacking these feedbacks

medium

1

train

797

AR6_WGI

526

2

In many cases, the models score similarly against both observational references, indicating that model errors are usually larger than observational uncertainties

high

2

train

798

AR6_WGI

526

3

Moreover, synthesizing across Sections 3.3–3.7, we assess that the CMIP6 multi-model mean captures most aspects of observed climate change well

high

2

train

799

AR6_WGI

528

27

Overall, the PMIP multi-model means agree very well (within 0.5°C of the assessed range) with GSAT reconstructed from proxies across multiple time periods, spanning a range from 6°C colder than pre-industrial (Last Glacial Maximum) to 14°C warmer than pre-industrial (Early Eocene Climate Optimum)

high

2

train