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1,500
AR6_WGI
1,280
1
Furthermore, parts of the EAIS have lost mass in the last two decades
high
2
train
1,501
AR6_WGI
1,280
2
As stated in SROCC, snowfall and glacier flow are the largest components determining AIS mass changes, with glacier flow acceleration (dynamic thinning) on the WAIS and the Antarctic Peninsula driving total loss trends in recent decades (very high confidence), and a partial offset of the dominating dynamic-thinning losses by increased snowfall
high
2
train
1,502
AR6_WGI
1,281
6
In summary, ice-shelf thinning, mainly driven by basal melt, is widespread around the Antarctic coast and particularly strong around the WAIS
high
2
train
1,503
AR6_WGI
1,281
28
In summary, the observed evolution of the ASE glaciers is compatible with, but not unequivocally indicating an ongoing MISI
medium
1
train
1,504
AR6_WGI
1,285
28
The SROCC assessed that ice-sheet interactions with the solid Earth are not expected to substantially slow sea level rise from marine-based ice in Antarctica over the 21st century
medium
1
train
1,505
AR6_WGI
1,285
32
Grounding line stabilization by the solid Earth response may therefore occur over the 21st century in the Amundsen Sea Embayment, where most mass loss is occurring (Section 9.4.2.1), but more generally occurs over multi-centennial to millennial time scales
medium
1
train
1,506
AR6_WGI
1,288
12
In summary, it is likely that the AIS will continue to lose mass throughout this century under all emissions scenarios – that is, dynamic losses driven by ocean warming and ice-shelf disintegration will likely continue to outpace increasing snowfall
medium
1
train
1,507
AR6_WGI
1,288
32
The SR1.5 (Hoegh-Guldberg et al., 2018) assessed that a threshold for WAIS instability may be close to 1.5°C–2°C
medium
1
test
1,508
AR6_WGI
1,289
9
Overall, increased evidence and agreement on the time scales and drivers of mass loss confirm the SR1.5 assessment that a threshold for WAIS instability may be close to 1.5°C–2°C (medium confidence), and that the probability of passing a threshold is larger for 2°C warming than for 1.5°C
medium
1
train
1,509
AR6_WGI
1,289
10
New projections agree with previous studies that only part of WAIS would be lost on multi-century time scales if warming remains less than 2°C
medium
1
train
1,510
AR6_WGI
1,289
12
Under around 2°C–3°C peak warming, complete or near-complete loss of the WAIS is projected in most studies after multiple millennia, with continent-wide mass losses of around 2–5 m SLE or more; this could occur on multi-century time scales under very high basal melting (Lipscomb et al., 2021) or widespread ice-shelf loss and/or MICI
low
0
test
1,511
AR6_WGI
1,289
14
If warming exceeds around 3°C above pre-industrial, part of the EAIS (typically the Wilkes Subglacial Basin) is projected to be lost on multi-millennial time scales
low
0
train
1,512
AR6_WGI
1,289
17
The SROCC (Meredith et al., 2019; Oppenheimer et al., 2019) assessed that Antarctic mass losses could be irreversible over decades to millennia
low
0
train
1,513
AR6_WGI
1,289
22
New research therefore confirms SROCC assessment that mass loss from the AIS is irreversible on decadal to millennial time scales (low confidence) (FAQ 9.1), and suggests that reducing atmospheric CO 2 concentrations or temperatures to pre-industrial levels may not be sufficient to prevent or reverse substantial Antarctic mass losses
low
0
train
1,514
AR6_WGI
1,291
15
Including the peripheral glaciers of the ice sheets, the global glacier mass loss rate in the period 2000–2019 is very likely 266 ± 16 Gt yr –1 (4 [3 to 6] % of glacier mass in 2000) with an increase in the mass loss rate from 240 ± 9 Gt yr –1 in 2000–2009 to 290 ± 10 Gt yr –1 in 2010–2019
high
2
train
1,515
AR6_WGI
1,291
17
In summary, new evidence published since SROCC shows that, during the decade 2010–2019, glaciers lost more mass than in any other decade since the beginning of the observational record
very high
3
train
1,516
AR6_WGI
1,292
7
For all regions with long-term observations, glacier mass in the decade 2010–2019 was the smallest since at least the beginning of the 20th century
medium
1
train
1,517
AR6_WGI
1,292
12
There is limited evidence to assess whether the Karakoram anomaly will persist in coming decades but, due to the projected increase in air temperature throughout the region, its long-term persistence is unlikely
high
2
train
1,518
AR6_WGI
1,295
3
The SROCC assessed that global glacier mass loss by 2100, relative to 2015 will be 18 [likely range 11 to 25] % for scenario RCP2.6 and 36 [likely range 26 to 47] % for RCP8.5, and that many glaciers will disappear regardless of the emissions scenario
very high
3
train
1,519
AR6_WGI
1,295
6
Glaciers will lose 29,000 [9000 to 49,000] Gt and 58,000 [28,000 to 88,000] Gt over the period 2015–2100 for RCP2.6 and RCP8.5, respectively
medium
1
train
1,520
AR6_WGI
1,296
4
In summary, both global and regional studies agree that glacier mass loss will continue in all regions, with larger mass loss for high-emissions scenarios
high
2
train
1,521
AR6_WGI
1,296
19
It is also found in high-altitude areas of mountain ranges in both hemispheres – estimated in SROCC (Hock et al., 2019b) as representing about 27–29% of the global permafrost area
medium
1
train
1,522
AR6_WGI
1,300
7
Analysis of paleoclimate records (Pederson et al., 2011; Belmecheri et al., 2016) suggests that recent snowpack reductions in western North America are exceptional on a millennial time scale
medium
1
train
1,523
AR6_WGI
1,303
10
In summary, consistent projections from all generations of global climate models, elementary process understanding and strong covariance between snow cover and temperature on several time scales make it virtually certain that future Northern Hemisphere snow cover extent and duration will continue to decrease as global climate continues to warm, and process understanding strongly suggests that this also applies to Southern Hemisphere seasonal snow cover
high
2
train
1,524
AR6_WGI
1,303
18
Based on these updated data and methods, the GMSL change over the (pre-satellite) period 1901–1990 is assessed to be 0.12 [0.07 to 0.17, very likely range] m with an average rate of 1.35 [0.78 to 1.92, very likely range] mm yr –1
high
2
train
1,525
AR6_WGI
1,303
20
The SROCC found that four of the five available tide gauge reconstructions that extend back to at least 1902 showed a robust acceleration
high
2
train
1,526
AR6_WGI
1,304
16
For the periods 1901–1990 and 1901–2018, the assessed very likely range for the sum of components is found to be consistent with the assessed very likely range of observed GMSL change
medium
1
train
1,527
AR6_WGI
1,304
19
While the combined mass loss for Greenland and glaciers is consistent with SROCC, updates in the underlying datasets lead to differences in partitioning of the mass loss.9.6.1.2 Global Mean Sea Level Change Budget in the Satellite Era The SROCC (Oppenheimer et al., 2019) concluded that GMSL increased at a rate of 3.16 [2.79 to 3.53, very likely range] mm yr –1 in the period 1993–2015 (the satellite altimetry era), and a rate of 3.58 [3.10 to 4.06, very likely range] mm yr –1 in the period 2006–2015 – the Gravity Recovery and Climate Experiment (GRACE)/Argo data era
high
2
train
1,528
AR6_WGI
1,304
20
An updated assessment for the periods 1993–2018 and 2006–2018 yields values of 3.25 [2.88 to 3.61] and 3.69 [3.21 to 4.17] mm yr –1
high
2
train
1,529
AR6_WGI
1,304
21
Based on the GMSL assessed time series presented in Section 2.3.3.3, GMSL acceleration is estimated as 0.075 [0.066 to 0.080] mm yr –2 for 1971–2018 and 0.094 [0.082–0.115] mm yr –2 for 1993–2018
high
2
train
1,530
AR6_WGI
1,304
26
For both periods in the satellite era – that is, 1993–2018 and 2006–2018 – the sum of contributions is consistent with the total observed GMSL change
high
2
train
1,531
AR6_WGI
1,304
31
Because of the increased ice-sheet mass loss, the total loss of land ice (glaciers and ice sheets) was the largest contributor to GMSL rise over the period 2006–2018
high
2
train
1,532
AR6_WGI
1,306
17
In summary, the regional sea level budget, using either observations or models, can currently only be closed on basin scales
medium
1
train
1,533
AR6_WGI
1,307
14
Adding the projected sea level change from land ice mass loss and groundwater extraction strengthens and modifies the forced signal, leading to times of emergence 10 to 20 years earlier in most parts of the ocean, except in regions close to sources of mass loss, with emergence over 50% of the ocean area by 2020, and nearly everywhere by 2100
medium
1
train
1,534
AR6_WGI
1,307
15
In summary, detection of forced regional changes for some ocean areas in recent decades is possible
medium
1
train
1,535
AR6_WGI
1,308
6
The SROCC assessment that past multi-metre sea level changes have resulted from significant ice-sheet changes beyond those presently observed is confirmed (very high confidence).Cross-Chapter Box 9.1 (continued) The Earth system gained substantial energy over the period 1971–2018
high
2
train
1,536
AR6_WGI
1,308
7
Ocean warming dominates the energy inventory change
high
2
train
1,537
AR6_WGI
1,308
14
A related assessment presented in Chapter 7 demonstrates closure of the global energy budget
high
2
train
1,538
AR6_WGI
1,309
3
Partly on the basis of these studies, SROCC proposed a ‘plausible’ upper bound on GMSL of 25 m
low
0
train
1,539
AR6_WGI
1,309
4
Ice-sheet model simulations indicate that Northern Hemisphere glaciation was limited to high-elevation regions in eastern and southern Greenland
medium
1
train
1,540
AR6_WGI
1,309
5
Southern Hemisphere glaciation was characterized by an Antarctic Ice Sheet (AIS) reduced in volume from the present
medium
1
train
1,541
AR6_WGI
1,309
7
In summary, under a past warming level of around 2.5°C–4°C, ice sheets in both hemispheres were reduced in extent compared to present
high
2
train
1,542
AR6_WGI
1,309
8
Proxy-based evidence (Section 2.3.3.3) combined with numerical modelling indicates that, on millennial time scales, the GMSL contribution arising from ice sheets was >5 m (high confidence) or >10 m
medium
1
train
1,543
AR6_WGI
1,309
12
The GMSL was 6–13 m above present
medium
1
train
1,544
AR6_WGI
1,309
16
In summary, geological reconstructions and numerical simulations consistently show that past warming levels of <2°C (GMST) are sufficient to trigger multi- metre mass loss from both the Greenland and Antarctic ice sheets if maintained for millennia
high
2
train
1,545
AR6_WGI
1,309
21
Since AR5, information has improved about the LIG, when GMST was about 0.5°C–1.5°C above 1850–1900
medium
1
train
1,546
AR6_WGI
1,309
24
It is virtually certain that GMSL was higher than today, likely by 5–10 m
medium
1
train
1,547
AR6_WGI
1,310
15
Of the residual, up to about 1.4 m may be ascribed to groundwater, leaving a shortfall of 16 ± 10 m yet to be allocated among land ice reservoirs or lakes.9.6.2.5 Last Deglacial Transition: Meltwater pulse 1A During Meltwater pulse 1A (MWP-1A), GMSL very likely
medium
1
train
1,548
AR6_WGI
1,310
22
In summary, MWP-1A appears to have been driven by a combination of melt in North America (high confidence), Eurasia (low confidence), and Antarctica
low
0
train
1,549
AR6_WGI
1,310
32
At 6 ka, GMSL was –3.5 to +0.5 m
medium
1
train
1,550
AR6_WGI
1,311
1
Geochronological and numerical modelling studies indicate that it is likely
medium
1
train
1,551
AR6_WGI
1,311
11
In summary, higher-than-pre-industrial GMST during the mid-Holocene coincided with recession of the Greenland Ice Sheet to a smaller-than-present extent
high
2
train
1,552
AR6_WGI
1,311
14
In summary, both proxies and model simulations indicate that GMSL changes during the early to mid-Holocene were the result of episodic pulses, due to drainage of meltwater lakes, superimposed on a trend of steady rise due to continued ice-sheet retreat
high
2
train
1,553
AR6_WGI
1,311
15
The combination of tide gauge observations and geological reconstructions indicates that a sustained increase of GMSL began between 1820–1860 and led to a 20th-century GMSL rise that was very likely
high
2
train
1,554
AR6_WGI
1,311
19
In summary, rates of RSL rise exceeding the pre-industrial background rate of rise are apparent in parts of the North Atlantic in the 19th century (medium confidence), and in most of the world in the 20th century
high
2
train
1,555
AR6_WGI
1,313
2
Considering also projections incorporating MICI or SEJ
low
0
train
1,556
AR6_WGI
1,316
21
RSL rise associated with GRD is very likely to be largest in the Pacific, due to the combined effects of projected GrIS, AIS and glacier mass loss
high
2
train
1,557
AR6_WGI
1,316
24
In parts of north-eastern North America and north-western Europe, GRD effects associated with mass loss from southern Greenland will lead to an RSL fall, whereas mass loss from northern Greenland will lead to an RSL rise
high
2
train
1,558
AR6_WGI
1,318
13
In particular, under SSP5-8.5, low-confidence processes could lead to a total GMSL rise of 0.6–1.6 m over this time period (17th–83rd percentile range of p-box, including SEJ- and MICI-based projections), with 5th–95th percentile projections extending to 0.5–2.3 m
low
0
train
1,559
AR6_WGI
1,319
5
Approximately 60% (SSP1-1.9) to 70% (SSP5-8.5) of the global coastline has a projected median 21st century regional RSL rise within ±20% of the global mean m 1950 2000 2050 2100 2150 00.511.522.5 SSP5-8.5 SSP3-7.0 SSP2-4.5 SSP1-2.6 SSP1-1.9 HistoricalMedian (medium confidence) Likely range
medium
1
train
1,560
AR6_WGI
1,320
1
Consistent with AR5, loss of land ice mass will be an important contributor to spatial patterns in RSL change (high confidence), with ocean dynamic sea level being particularly important as a dipolar contributor in the north-west Atlantic, a positive contributor in the Arctic Ocean, and a negative contributor in the Southern Ocean south of the Antarctic Circumpolar Current
medium
1
train
1,561
AR6_WGI
1,320
2
As today, VLM will remain a major driver of RSL change
high
2
train
1,562
AR6_WGI
1,320
3
Uncertainty in RSL projections is greatest in tectonically active areas in which VLM varies over short distances (e.g., Alaska) and in areas potentially subject to large ocean dynamic sea level change (e.g., the north-western Atlantic)
high
2
train
1,563
AR6_WGI
1,321
12
The SROCC projected 0.6–1.0 m under RCP2.6 and 2.3–5.3 m under RCP8.5
low
0
train
1,564
AR6_WGI
1,322
2
Under SSP5-8.5, GMSL will rise between 1.7 and 6.8 m by 2300 in the absence of MICI and by up to 16 m considering MICI, a wider range than AR5 or SROCC assessments, but consistent with published projections
low
0
train
1,565
AR6_WGI
1,323
3
On the basis of modelling studies, paleo constraints, single-ice-sheet studies finding multimillennial nonlinear responses from both the Greenland and Antarctic ice sheets (Sections 9.4.1.4 and 9.4.2.6), and the underlying physics, we conclude that GMSL commitment is nonlinear in peak warming on time scales of both 2,000 and 10,000 years
medium
1
train
1,566
AR6_WGI
1,323
4
Although thermosteric sea level will start to decline slowly about 2,000 years after emissions cease, the slower responses from the Greenland and Antarctic ice sheets mean that GMSL will continue to rise for 10,000 years under most scenarios
medium
1
train
1,567
AR6_WGI
1,323
10
Carbon dioxide removal, solar radiation modification, and local ice-shelf engineering may be effective at reducing the yet-to-be- realized sea level commitment, but ineffective at reversing GMSL rise
low
0
test
1,568
AR6_WGI
1,324
6
In doing so, we note upfront that the main uncertainty related to high-end sea level rise is ‘when’ rather than ‘if’ it arises: the upper limit of 1.01 m of likely sea level range by 2100 for the SSP5-8.5 scenario will be exceeded in any future warming scenario on time scales of centuries to millennia
high
2
train
1,569
AR6_WGI
1,325
6
As in AR5 and SROCC, tide gauge observations show that RSL rise (Section 9.6.1.3) is the primary driver of changes in ESWL at most locations and, across tide gauges, has led to a median 165% increase in high-tide flooding over 1995–2014 relative to those over 1960–1980
high
2
train
1,570
AR6_WGI
1,325
7
Some locations exhibit substantial differences between long-term RSL trends and ESWL
high
2
train
1,571
AR6_WGI
1,325
11
Failing to consider the non-linear interactions between tide, surge and RSL may overestimate trends in ESWL
low
0
train
1,572
AR6_WGI
1,326
3
Combined, observations and models indicate RSL rise and direct anthropogenic factors are the primary drivers of observed tidal changes at tide gauge stations
medium
1
train
1,573
AR6_WGI
1,326
17
On the basis of satellite altimeter observations, SROCC reported increasing extreme wave heights in the Southern and North Atlantic oceans of around 1.0 and 0.8 cm yr –1, respectively, over the period 1985–2018
medium
1
train
1,574
AR6_WGI
1,326
18
The SROCC (Collins et al., 2019) also identified sea ice loss in the Arctic as leading to increased wave heights over the period 1992–2014
medium
1
train
1,575
AR6_WGI
1,326
26
However, sensitivity of processing techniques, inadequate spatial distribution of observations, and homogeneity issues in available records limit confidence in reported trends
medium
1
train
1,576
AR6_WGI
1,326
28
Detection and attribution of the human influence on climatic changes in surges, and waves remains a challenge (Ceres et al., 2017), with limited evidence to suggest in some instances – for example, poleward migration of tropical cyclones in the Western North Pacific (Section 11.7.1.2), changes in surges and waves can be attributed to anthropogenic climate change
low
0
train
1,577
AR6_WGI
1,326
30
The close relationship between local ESL and long-term RSL change, combined with the robust attribution of GMSL change (Section 9.6.1.4), implies that observed global changes in ESL can be attributed, at least in part, to human-caused climate change
medium
1
train
1,578
AR6_WGI
1,328
8
The SROCC showed that currently rare ESL events (e.g., with an average return period of 100 years) will occur annually or more frequently at most available locations for RCP4.5 by the end of the century
high
2
train
1,579
AR6_WGI
1,328
17
By 2100, the median frequency amplification factor is projected to be 163 for SSP1-2.6, 325 for SSP2-4.5, and 532 for SSP5-8.5, with respectively 60%, 71%, and 82% of the stations experiencing a currently 1% annual probability event at least yearly
medium
1
train
1,580
AR6_WGI
1,328
28
In summary, despite waves and surges being non-negligible contributors to projected ETWL and ECWL changes (Vousdoukas et al., 2018; Melet et al., 2020), RSL change is expected to be the main driver in changes in future ESL return periods in most areas
medium
1
train
1,581
AR6_WGI
1,328
32
At local and regional scales, anthropogenic factors such as major land reclamation efforts, as in the East China Sea (Song et al., 2013) or differing national coastal management strategies (maintaining the present coastline position or managed retreat) will locally modulate the influence of GMSL rise on tidal amplitude
medium
1
train
1,582
AR6_WGI
1,330
11
Thus, projections of ESL that do not consider correlations between and among sea level forced and atmospherically forced drivers can differ strongly from coupled projections
medium
1
train
1,583
AR6_WGI
1,330
12
The SROCC (Collins et al., 2019) highlighted compound events, or coincident occurrence of multiple hazards, as an example of deep uncertainty, and noted that failing to account for multiple factors contributing to extreme events will lead to underestimation of the probabilities of occurrence
high
2
train
1,584
AR6_WGI
1,382
10
Distilling regional climate information from multiple lines of evidence and taking the user context into account will increase the fitness, usefulness and relevance for decision-making and enhances the trust users will have in applying it
high
2
train
1,585
AR6_WGI
1,382
13
Taking the values of the relevant actors into account when co-producing climate information, and translating this information into the broader user context, improves the usefulness and uptake of this information
high
2
train
1,586
AR6_WGI
1,382
15
The availability of multiple observational records, including reanalyses, that are fit for evaluating the phenomena of interest and account for observational uncertainty, are fundamental for both understanding past regional climate change and assessing climate model performance at regional scales
high
2
train
1,587
AR6_WGI
1,382
16
Employing tailored, process-oriented and potentially multivariate diagnostics to evaluate whether a climate model realistically simulates relevant aspects of present-day regional climate increases trust in future projections of these aspects
high
2
train
1,588
AR6_WGI
1,382
18
Precipitation measurements in mountainous areas, especially of solid precipitation, are strongly affected by gauge location and setup
very high
3
train
1,589
AR6_WGI
1,382
23
Regional reanalyses represent the distributions of precipitation, surface air temperature, and surface wind, including the frequency of extremes, better than global reanalyses
high
2
train
1,590
AR6_WGI
1,382
26
Global models by themselves provide a useful line of evidence for the construction of regional climate information through the attribution or projection of forced changes or the quantification of the role of the internal variability
high
2
train
1,591
AR6_WGI
1,382
27
Dynamical downscaling using regional climate models adds value in representing many regional weather and climate phenomena, especially over regions of complex orography or with heterogeneous surface characteristics
very high
3
test
1,592
AR6_WGI
1,382
28
Increasing climate model resolution improves some aspects of model performance
high
2
train
1,593
AR6_WGI
1,382
29
Some local-scale phenomena such as land–sea breezes and mountain wind systems can only be realistically represented by simulations at a resolution of the order of 10 km or finer
high
2
train
1,594
AR6_WGI
1,382
30
Simulations at kilometre-scale resolution add value in particular to the representation of convection, sub-daily precipitation extremes (high confidence) and soil-moisture– precipitation feedbacks
medium
1
train
1,595
AR6_WGI
1,383
4
Including the relevant forcings (e.g., aerosols, land-use change and stratospheric ozone concentrations) and representing the relevant feedbacks (e.g., snow–albedo, soil-moisture–temperature, soil-moisture–precipitation) in global and regional models is a prerequisite for reproducing historical regional trends and ensuring fitness for future projections
high
2
train
1,596
AR6_WGI
1,383
5
The sign of projected regional changes of variables such as precipitation and wind speed is in some cases only simulated in a trustworthy manner if relevant regional processes are represented
medium
1
train
1,597
AR6_WGI
1,383
7
Statistical downscaling methods with carefully chosen predictors and an appropriate model structure for a given application realistically represent many statistical aspects of present-day daily temperature and precipitation
high
2
train
1,598
AR6_WGI
1,383
8
Bias adjustment has proven beneficial as an interface between climate model projections and impact modelling in many different contexts
high
2
train
1,599
AR6_WGI
1,383
9
Weather generators realistically simulate many statistical characteristics of present-day daily temperature and precipitation, such as extreme temperatures and wet- and dry-day transition probabilities
high
2
train