rlacombe/ClimateX huggingface dataset:
The SROCC highlighted that future change of MHWs will not be globally uniform, with the largest changes in the frequency of marine heatwaves being projected to occur in the western tropical Pacific and the Arctic Ocean (IPCC AR6_WGI, confidence: medium)
Moderate increases are projected for mid-latitudes, and only small increases are projected for the Southern Ocean (IPCC AR6_WGI, confidence: medium)
The resolution of current climate models (CMIP5 and CMIP6) capture the broad features of MHWs, but they may have a bias towards weaker and longer MHWs in the historical period (IPCC AR6_WGI, confidence: medium)
Section 2.3.3.1 reports that current multi-decadal to centennial rates of OHC gain are greater than at any point since the last deglaciation (IPCC AR6_WGI, confidence: medium)
Section 3.5.1.3 assessed that 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 (IPCC AR6_WGI, confidence: very high)
In summary, in the upper 2000 m since the 1970s, the subpolar North Atlantic has been slowly warming, and the Southern Ocean has stored a disproportionally large amount of anthropogenic heat (IPCC AR6_WGI, confidence: medium)
In summary, and strengthening SROCC assessment, ocean warming is not globally uniform due to patterns of uptake predominantly along known water mass pathways, and due to changing ocean circulation redistributing heat within the ocean (IPCC AR6_WGI, confidence: high)
Despite a decrease of AMOC northward heat (0.17 PW) and mass (2.5 Sverdrup (Sv); 1 Sv = 109 kg s–1) transport, OHT has increased toward the Arctic through increased upper northern North Atlantic temperatures and stronger wind-driven gyres (IPCC AR6_WGI, confidence: medium)
In summary, OHT has increased toward the Arctic in recent decades, which at least partially explains the recent OHC change in the Arctic (IPCC AR6_WGI, confidence: medium)
In summary, climate models have more skill in representing OHC change from added heat than from ocean circulation change (IPCC AR6_WGI, confidence: high)
In summary, on decadal time scales, redistribution will dominate regional patterns of OHC change without affecting the globally integrated OHC; however, by 2100, particularly under strong warming scenarios, there is high confidence that regional patterns of OHC change will be dominated by added heat entering the sea surface, primarily in water mass formation regions in the subtropics; and reduced aerosols will increase the relative rate of Northern Hemisphere heat uptake (IPCC AR6_WGI, confidence: medium)
Section 2.3.3.2 strengthens evidence that subsurface salinity trends are connected to surface trends (very likely), which are, in turn, linked to an intensifying hydrological cycle (IPCC AR6_WGI, confidence: medium)
Section 3.5.2.1 reports, however, that the fidelity of ocean salinity simulation has improved in CMIP6, and near-surface and subsurface biases have been reduced (IPCC AR6_WGI, confidence: medium)
Projections confirm SROCC assessment that fresh ocean regions will continue to get fresher and salty ocean regions will continue to get saltier in the 21st century (IPCC AR6_WGI, confidence: medium)
Consistently, we assess that STMW have deepened worldwide, with greatest deepening in the Southern Hemisphere (IPCC AR6_WGI, confidence: high)
The SROCC connected SAMW and AAIW to Southern Ocean temperature changes as the large Southern Ocean surface heat uptake is circulated and mixed along with these water masses (IPCC AR6_WGI, confidence: high)
The SROCC (Collins et al., 2019) assessed that in situ observations (2004–2017) and sea surface temperature reconstructions indicate that AMOC has weakened relative to 1850–1900 (IPCC AR6_WGI, confidence: medium)
This suggests that the observed AMOC-shift between 2007 and 2011 may be part of a longer-term decrease (IPCC AR6_WGI, confidence: medium)
Projected AMOC decline by 2100 ranges from 24 [4 to 46] % in SSP1-2.6 to 39 [17–55] % in SSP5-8.5 (IPCC AR6_WGI, confidence: medium)
Tuning towards stability and model biases (Valdes, 2011; Liu et al., 2017; Mecking et al., 2017; Weijer et al., 2019) provides CMIP models a tendency toward unrealistic stability (IPCC AR6_WGI, confidence: medium)
It also reported that, instead of increasing the mean ACC transport, additional energy input associated with increased wind stress cascades into the eddy field (IPCC AR6_WGI, confidence: medium)
For the lower cell overturning circulation, SROCC assessed that a slowdown of its transport is consistent with the observed decrease in volume (IPCC AR6_WGI, confidence: medium)
Section 2.4 concludes that a sustained shift beyond multi-centennial variability has not been observed for El Niño–Southern Oscillation (ENSO) (IPCC AR6_WGI, confidence: medium)
In summary, while future changes in tropical modes of variability remain unclear, change in atmospheric and ocean circulation will drive continued change in tropical ocean temperature in the 21st century (medium confidence), with part of the region experiencing drastic marine heat wave conditions (IPCC AR6_WGI, confidence: high)
Section 2.3.3.4 assesses that, while WBC strength is highly variable at multi-decadal scale (high confidence), WBCs and subtropical gyres have shifted poleward since 1993 (IPCC AR6_WGI, confidence: medium)
In the North Pacific, there has been an increasing trend in the Alaska Gyre from 1993 to 2017 (Cummins and Masson, 2018), which might be attributed to Pacific Decadal Oscillation (IPCC AR6_WGI, confidence: low)
All climate models reproduce WBCs and gyres, but eddy- present or eddy-rich models (roughly 10–25 km and about 10 km resolution, respectively) represent these currents more realistically than eddy-parameterized models (IPCC AR6_WGI, confidence: very high)
Increased resolution admits mesoscale eddies, and also improves simulation of the strength and position of WBCs such as the Kuroshio Current, Gulf Stream, and East Australian Current (IPCC AR6_WGI, confidence: very high)
The wind-current feedback, implemented by considering relative velocity of currents and wind, realistically dampens mesoscale eddies and WBCs, through mesoscale air–sea interaction (Ma et al., 2016; Renault et al., 2016, 2019), even though sub-mesoscale wind- current damping feedback is missing in these models (IPCC AR6_WGI, confidence: medium)
As eddies potentially play a role in determining the strength of gyre circulations and their low- frequency variability (Fox-Kemper and Pedlosky, 2004; Berloff et al., 2007), it is expected that eddy-present and eddy-rich models will differ in their decadal variability and sensitivity to changes in the wind stress of gyres from eddy-parameterized models (IPCC AR6_WGI, confidence: medium)
The SROCC (Collins et al., 2019) concluded with high confidence that Indonesian Throughflow (ITF) transport from the Pacific Ocean to the Indian Ocean has increased in the past two decades as a result (IPCC AR6_WGI, confidence: medium)
Projected future annual cumulative upwelling wind changes at most locations, and seasons remain within ±10–20% of present-day values in the 21st century, even in the context of high-end emissions scenarios (4×CO 2 or RCP8.5) (IPCC AR6_WGI, confidence: medium)
Change in upper-ocean stratification (Section 9.2.1.3) is projected to increase confinement of upwelling vertical velocities to near the ocean surface (IPCC AR6_WGI, confidence: high)
The California Current system has experienced some upwelling-favourable wind intensification since the 1980s (IPCC AR6_WGI, confidence: high)
New evidence reinforces our confidence in SROCC assessment that, under increased radiative forcing, EBUS winds will change with a dipole spatial pattern within each EBUS of reduction (weaker and/or shorter) at low latitude, and enhancement (stronger and/or longer) at high latitude (IPCC AR6_WGI, confidence: high)
Thus, while conversions between OHC, mean ocean temperature and GMTSL across applications are within uncertainty ranges (IPCC AR6_WGI, confidence: medium)
Patterns of change are consistent between model simulations and observations (IPCC AR6_WGI, confidence: medium)
Projections of dynamic sea level variability require fully three-dimensional ocean models, and only high-resolution ocean models are statistically consistent on short time scales with satellite altimeter observations (IPCC AR6_WGI, confidence: very high)
The SROCC (Meredith et al., 2019) assesses that sea ice extent, which is the total area of all grid cells with at least 15% sea ice concentration, has declined since 1979 in each month of the year (IPCC AR6_WGI, confidence: very high)
Sea ice area has decreased in every month of the year from 1979 to the present (IPCC AR6_WGI, confidence: very high)
The absolute and the relative ice losses are highest in late summer-early autumn (IPCC AR6_WGI, confidence: high)
Averaged over the decade 2010–2019, the monthly Arctic sea ice area from August to October has been around 2 million km² (or about 25%) smaller than during 1979–1988 (IPCC AR6_WGI, confidence: high)
In the Bering Sea, expanding winter sea ice cover was observed until 2017 (Frey et al., 2015; Onarheim et al., 2018; Peng and Meier, 2018), but a marked reduction in sea ice concentration has occurred since then (IPCC AR6_WGI, confidence: high)
Since 1953, the years 2015 to 2018 had the four lowest values of maximum Arctic sea ice area, which usually occurs in March (IPCC AR6_WGI, confidence: high)
These records and other proposed paleo proxies, including bromine in ice cores (Spolaor et al., 2016), dinocyst assemblages (e.g., De Vernal et al., 2013b) and driftwood (e.g., Funder et al., 2011), provide evidence of sea ice fluctuations that exceed internal variability (IPCC AR6_WGI, confidence: high)
The SROCC assessed that approximately half of the satellite-observed Arctic summer sea ice loss is driven by increased concentrations of atmospheric greenhouse gases (IPCC AR6_WGI, confidence: medium)
In addition to changes in the external forcing, internal variability substantially affects Arctic sea ice, evidenced from both paleorecords (e.g., Chan et al., 2017; Hörner et al., 2017; Kolling et al., 2018) and satellites after 1979 (e.g., Notz and Stroeve, 2018; Roberts et al., 2020) (IPCC AR6_WGI, confidence: high)
In examining temperature thresholds for the loss of Arctic summer sea ice, the Special Report on Global Warming of 1.5°C (SR1.5; Hoegh-Guldberg et al., 2018) and SROCC assess that a reduction of September mean sea ice area to below 1 million km2, practically a sea ice-free Arctic Ocean, is more probable for a global mean warming of 2°C compared to global mean warming of 1.5°C (IPCC AR6_WGI, confidence: high)
Quantitatively, existing studies (Screen and Williamson, 2017; Jahn, 2018; Ridley and Blockley, 2018; Sigmond et al., 2018; Notz and SIMIP Community, 2020) also show that, for a warming between 1.5 and 2°C, the Arctic will only be practically sea ice free in September in some years, while at 3°C warming, the Arctic is practically sea ice free in September in most years, with longer practically sea ice-free periods at higher warming levels (IPCC AR6_WGI, confidence: medium)
In addition, there is no tipping point or critical threshold in global mean temperature beyond which the loss of summer sea ice becomes self-accelerating and irreversible (IPCC AR6_WGI, confidence: high)
The loss of winter sea ice is reversible as well, but the loss of winter sea ice area per degree of warming in CMIP5 and CMIP6 projections increases as the ice retreats from the continental shore lines, because these limit the possible areal fluctuations (IPCC AR6_WGI, confidence: high)
As assessed by SROCC, the evolution of mean Antarctic sea ice area is the result of opposing regional trends (IPCC AR6_WGI, confidence: high)
The changes in stratification result partly from surface freshening (De Lavergne et al., 2014), associated with increased northward sea ice advection (Haumann et al., 2020) and/or melting of the Antarctic ice sheet (IPCC AR6_WGI, confidence: medium)
In the Amundsen Sea, strong ice shelf melting can cause local sea ice melt next to the ice shelf front by entraining warm circumpolar deep water to the ice shelf cavity and surface ocean (IPCC AR6_WGI, confidence: medium)
Paleo-proxy data indicate that, on multi-decadal to multi-centennial time scales, sea ice coverage of the Southern Ocean follows large-scale temperature trends (e.g., Crosta et al., 2018; Chadwick et al., 2020; Lamping et al., 2020), for example linked to fluctuations in the El Niño–Southern Oscillation and Southern Annular Mode (Crosta et al., 2021), and that during the Last Glacial Maximum, Antarctic sea ice extended to about the polar front latitude in most regions during winter, whereas the extent during summer is less well understood (e.g., Benz et al., 2016; Xiao et al., 2016; Nair et al., 2019).Regionally, proxy data from ice cores consistently indicate that the increase of sea ice area in the Ross Sea and the decrease of sea ice area in the Bellingshausen Sea are part of longer centennial trends and exceed internal variability on multi-decadal time scales (IPCC AR6_WGI, confidence: medium)
Data from ICESat-1 laser altimetry (Kurtz and Markus, 2012), from Operation IceBridge (Kwok and Kacimi, 2018), and long-term shipboard observations collected in the Antarctic Sea Ice Processes and Climate (ASPeCt) dataset (Worby et al., 2008) suggest that sea ice thicker than 1 m prevails in regions of multi-year ice along the eastern coast of the Antarctic Peninsula in the Weddell Sea, in the high-latitude embayment of the Weddell Sea, and along the coast of the Amundsen Sea, with remaining regions dominated by thinner first-year sea ice (IPCC AR6_WGI, confidence: high)
In summary, the detailed regional records show an increase in mass loss in all regions after the 1980s, caused by both increases in discharge and decreases in SMB (IPCC AR6_WGI, confidence: high)
The largest mass loss occurred in the north-west and the south-east of Greenland (IPCC AR6_WGI, confidence: high)
The SROCC stated that surface processes, rather than ice discharged into the ocean, will dominate Greenland ice loss over the 21st century, regardless of the emissions scenario (IPCC AR6_WGI, confidence: high)
The projected mass loss of Greenland is predominantly due to increased surface meltwater and loss in refreezing capacity resulting in decreasing SMB (IPCC AR6_WGI, confidence: high)
The SROCC adopted the AR5 assessment that complete loss of Greenland ice, contributing about 7 m to sea level, over a millennium or more would occur for a sustained global mean surface temperature (GMST) between 1°C (low confidence) and 4°C (IPCC AR6_WGI, confidence: medium)
Mass loss of the West Antarctic and Antarctic Peninsula ice sheets has increased since about 2000 (IPCC AR6_WGI, confidence: very high)
In summary, WAIS losses, through acceleration, retreat and thinning of the principal outlet glaciers, dominated the AIS mass losses over the last decades (IPCC AR6_WGI, confidence: very high)
Furthermore, parts of the EAIS have lost mass in the last two decades (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: high)
In summary, ice-shelf thinning, mainly driven by basal melt, is widespread around the Antarctic coast and particularly strong around the WAIS (IPCC AR6_WGI, confidence: high)
In summary, the observed evolution of the ASE glaciers is compatible with, but not unequivocally indicating an ongoing MISI (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: medium)
The SR1.5 (Hoegh-Guldberg et al., 2018) assessed that a threshold for WAIS instability may be close to 1.5°C–2°C (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: low)
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 (IPCC AR6_WGI, confidence: low)
The SROCC (Meredith et al., 2019; Oppenheimer et al., 2019) assessed that Antarctic mass losses could be irreversible over decades to millennia (IPCC AR6_WGI, confidence: low)
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 (IPCC AR6_WGI, confidence: low)
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 (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: very high)
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 (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: very high)
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 (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: high)
The SROCC found that four of the five available tide gauge reconstructions that extend back to at least 1902 showed a robust acceleration (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: high)
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 (IPCC AR6_WGI, confidence: high)
In summary, the regional sea level budget, using either observations or models, can currently only be closed on basin scales (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: medium)
In summary, detection of forced regional changes for some ocean areas in recent decades is possible (IPCC AR6_WGI, confidence: medium)
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 (IPCC AR6_WGI, confidence: high)
Ocean warming dominates the energy inventory change (IPCC AR6_WGI, confidence: high)
A related assessment presented in Chapter 7 demonstrates closure of the global energy budget (IPCC AR6_WGI, confidence: high)
Partly on the basis of these studies, SROCC proposed a ‘plausible’ upper bound on GMSL of 25 m (IPCC AR6_WGI, confidence: low)