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Freshwater discharge from ice sheets induces surface atmospheric cooling and subsurface ocean warming, which are associated with negative and positive feedbacks respectively. However, uncertainties persist regarding these feedbacks' relative strength and combined effect. Here we assess associated feedbacks in a coupled ice sheet-climate model, and show that for the Antarctic Ice Sheet the positive feedback dominates in moderate future warming scenarios and in the early stage of ice sheet retreat, but is overwhelmed by the negative feedback in intensive warming scenarios when the West Antarctic Ice Sheet undergoes catastrophic collapse. The Atlantic Meridional Overturning Circulation is affected by freshwater discharge from both the Greenland and the Antarctic ice sheets and, as an interhemispheric teleconnection bridge, exacerbates the opposing ice sheet's retreat via the Bipolar Seesaw. These results highlight the crucial role of ice sheet-climate interactions via freshwater flux in future ice sheet retreat and associated sea-level rise. Ice sheet freshwater discharge interacts with the climate and affects the ice sheet's sensitivity to climate change. This study shows that the overall feedback shifts from positive to negative as the pace of future warming intensifies [ABSTRACT FROM AUTHOR]

The evolution of Sahel summer rainfall in the context of global warming is a severe socio-economic concern because of its widespread influences on local agriculture, water resource management, food security, infrastructure planning, and ecosystems. Based on the mid-Pliocene simulations from the Pliocene Model Intercomparison Project Phase 2 and the historical simulations and shared socio-economic pathway 5–8.5 experiments from the Coupled Model Intercomparison Project phase 6, the present study contrasts the Sahel summer rainfall changes between the past mid-Pliocene and near future global warming climates. The results show that the Western African summer monsoon (WASM) circulation, closely linked with the Sahel summer rainfall change, tends to strengthen in both the past and future global warming climates, but the monsoonal circulation strengthening is much more intense in the past warm period than in the projected warm future. This causes that the multi-model ensemble (MME) mean increase ratio of Sahel summer rainfall in the past warming climate is about twice to three times larger than that in the future warming climate for the same increase of global mean surface temperature (the regional rainfall increase ratio in the MME mean: about 19.6% per one degree Celsius of global warming in the mid-Pliocene simulations versus about 7.7% per one degree Celsius of global warming in the SSP5-8.5 future projections). Such a striking discrepancy in the regional circulation and hydrological cycle changes is mainly attributed to a dramatically stronger warming over the Canadian Archipelago and Greenland during the mid-Pliocene warm period relative to the projected near future. The more significant northern high-latitude warming during the mid-Pliocene enhances the meridional temperature gradient between the extratropical and tropical regions, which could induce an excessive northward shift of the Intertropical Convergence Zone and a stronger WASM, and thus result in a more intense hydrological cycle around the Sahel region. Our results highlight that besides the global mean temperature increase, meridional warming patterns are also essential for the changes of WASM and regional hydrological cycle in a warmer world. Implications for projecting the regional monsoon and hydrological cycle changes at longer time scales than in the near future are discussed. [ABSTRACT FROM AUTHOR]

The climate-related melting of ice sheets and glaciers and the human-related redistribution of terrestrial water altered the Earth's gravity and displacement field and resulted in non-uniform sea level changes, i.e., sea level fingerprints (SLF). Satellite gravity is an important approach in monitoring the spatio-temporal evolution process of global terrestrial water storage (TWS) and its relevance to sea level changes. This study uses the mascon (mass concentration) product of Gravity Recovery and Climate Experiment (GRACE) and its Follow-on (GRACE-FO) to estimate the global TWS changes from 2002 to 2020. Subsequently, the global SLF caused by the redistribution of land and sea water mass is calculated based on the sea level equation, which includes both the self-attraction effect of loads and the feedback effect of the Earth's polar motion. Based on the results, the global TWS showed a decreasing trend (− 740.98 ± 41.64 Gt/year), with significant spatial differences. Consequently, the sea level maintained an upward trend (1.97 ± 0.10 mm/year), exhibiting typical fingerprint characteristics. Considering the sea level change (1.08 ± 0.10 mm/year) influenced by its steric variation, such as thermal expansion and salinity variation, we estimated that the total change rate of the global sea level is 3.05 ± 0.10 mm/year. The positive contribution of terrestrial water roughly amounted to 2.58 times the negative contribution. The melting of polar ice masses primarily contributes to the global TWS loss and sea level rise (0.46 ± 0.01 and 0.38 ± 0.02 mm/year for Greenland and Antarctica, respectively, excluding the peripheral glaciers). Another major contribution to sea level rise in the melting of glaciers (0.85 ± 0.01 mm/year, with the peripheral glaciers around Antarctica and Greenland). Furthermore, we found that the removal of coastline ice mass leads to the fingerprints effect, meaning that the relative sea level (RSL) does not increase but decreases around Greenland and Antarctica. Notably, the factors driving land-sea mass redistribution also include artificial reservoirs as well as groundwater and surface water, of which the latter has an overall smaller positive contribution (0.28 ± 0.07 mm/year) to the sea level rise. The role of artificial reservoirs in slowing down the sea level rise (− 0.57 ± 0.07 mm/year) cannot be ignored. [ABSTRACT FROM AUTHOR]

Ice sheet processes are often simplified in global climate models as changes in ice sheets have been assumed to occur over long time scales compared to ocean and atmospheric changes. However, numerous observations show an increasing rate of mass loss from the Greenland Ice Sheet and call for comprehensive process-based models to explore its role in climate change. Here, we present a new model system, EC-Earth-PISM, that includes an interactive Greenland Ice Sheet. The model is based on the EC-Earth v2.3 global climate model in which ice sheet surface processes are introduced. This model interacts with the Parallel Ice Sheet Model (PISM) without anomaly or flux corrections. Under pre-industrial climate conditions, the modeled climate and ice sheet are stable while keeping a realistic interannual variability. In model simulations forced into a warmer climate of four times the pre-industrial CO2 concentration, the total surface mass balance decreases and the ice sheet loses mass at a rate of about 500 Gt/year. In the climate warming experiments, the resulting freshwater flux from the Greenland Ice Sheet increases 55% more in the experiments with the interactive ice sheet and the climate response is significantly different: the Arctic near-surface air temperature is lower, substantially more winter sea ice covers the northern hemisphere, and the ocean circulation is weaker. Our results indicate that the melt-albedo feedback plays a key role for the response of the ice sheet and its influence on the changing climate in the Arctic. This emphasizes the importance of including interactive ice sheets in climate change projections. [ABSTRACT FROM AUTHOR]

The land surface beneath the Greenland and Antarctic Ice Sheets is isostatically suppressed by the mass of the overlying ice. Accurate computation of the land elevation in the absence of ice is important when considering, for example, regional geodynamics, geomorphology, and ice sheet behaviour. Here, we use contemporary compilations of ice thickness and lithospheric effective elastic thickness to calculate the fully re-equilibrated isostatic response of the solid Earth to the complete removal of the Greenland and Antarctic Ice Sheets. We use an elastic plate flexure model to compute the isostatic response to the unloading of the modern ice sheet loads, and a self-gravitating viscoelastic Earth model to make an adjustment for the remaining isostatic disequilibrium driven by ice mass loss since the Last Glacial Maximum. Feedbacks arising from water loading in areas situated below sea level after ice sheet removal are also taken into account. In addition, we quantify the uncertainties in the total isostatic response associated with a range of elastic and viscoelastic Earth properties. We find that the maximum change in bed elevation following full re-equilibration occurs over the centre of the landmasses and is +783 m in Greenland and +936 m in Antarctica. By contrast, areas around the ice margins experience up to 123 m of lowering due to a combination of sea level rise, peripheral bulge collapse, and water loading. The computed isostatic response fields are openly accessible and have a number of applications for studying regional geodynamics, landscape evolution, cryosphere dynamics, and relative sea level change. [ABSTRACT FROM AUTHOR]

Global sea level reconstruction (RecSL) for 1900–2015 was used to estimate the variations in oceanic kinetic energy (OKE) and compare OKE with changes in wind patterns and wind kinetic energy (WKE); the comparison was done for each latitude and for 5 western boundary currents (WBCs). Two contributors to variability in sea level were analyzed: gravitational, rotational and deformational effects (GRD) related to changes in water masses (barystatic sea level change), and changes in the sterodynamic sea level (SDSL), associated with changes in wind, steric sea level and ocean circulation. GRD changes were responsible for latitudinal multidecadal variations with time scale of ~ 60 to 80 years, while SDSL changes were responsible for interannual and decadal variability, and together with the Greenland ice melt, to sea level acceleration since the 1960s. Regional changes near WBCs show a coherent upward trend in OKE (+ 24% ± 3 increase per century), while trends in WKE over the same regions changed widely from -11% (decrease) over the Gulf Stream region to + 28% (increase) over the Brazil Current region. Low frequency oscillations of wind and oceanic kinetic energy are correlated in some WBCs (e.g., R = 0.5 in the Kuroshio region) but not in others (e.g., R = -0.05 in the Gulf Stream region). The study suggests that several forcing mechanisms contribute to the increased OKE, they include an increased wind-stress curl over subtropical gyres, local changes in wind patterns that impact some WBCs, and large uneven warming near WBCs that increased sea level gradients and thus intensified OKE. [ABSTRACT FROM AUTHOR]

The isotopic records of two 230Th-dated stalagmites from Longfugong Cave, Mt. Shennongjia, central China, reveal a highly resolved Asian summer monsoon (ASM) history from 29.5 to 14.5 ka BP. The two δ18O records are consistent with other Chinese cave δ18O records, suggesting that our new records are of regional significance. Due to the reservoir mixing of seepage water in the epikarst system, the stalagmite δ18O signals in this cave are more severely muted than those in other caves. Here, we observed that the amplitude of the δ13C variability is approximately twice that of the δ18O signal and can be used as a sensitive proxy of East Asian monsoon climates. First, the two stalagmite δ13C records are consistent with each other on decadal to centennial timescales. Second, there are high correlation coefficients between the δ13C and δ18O signals over shorter timescales. Third, from 25.2 to 19.6 ka BP, six peaks in the δ13C records were identified and are coincident with corresponding warming events in the Greenland ice-core δ18O records, suggesting that strong coupling occurred between the high- and low-latitude northern climates on centennial timescales. Therefore, we propose that atmospheric transmission mechanisms probably played an important role in linking the ASM and Greenland climates on short timescales. A shift in westerly winds associated with variability in the extent of temperature in the North Atlantic likely influenced changes in hydrological and thermal conditions at the cave site, leading to changes in vegetation cover and soil CO2 concentrations above the cave. Therefore, the calcite δ13C records probably had faster and more sensitive responses to rapid climate shifts compared with their related δ18O records. [ABSTRACT FROM AUTHOR]

New sea-level rise projections for Sweden are presented. Compared to earlier projections, we have here, more carefully, taken regional variations in sea-level rise into consideration. The better treatment of regional variations leads to lower sea-level rise projections for Sweden. However, recent research has also shown that Antarctic ice loss, in high emission scenarios, could be greater than what was believed earlier. Taking also this into account, we find a near cancellation between the increased Antarctic contribution and the decrease owing to the better treatment of spatial inhomogeneities. Sweden's sensitivity to melt from Antarctica and Greenland is also estimated using a new set of sea-level fingerprint kernels, and the sensitivity to melt from Greenland is found to be weak. To illustrate the influence mean sea-level rise has on extreme sea levels, it is also shown how the return period of sea-level extremes changes as a function of time owing to mean sea-level rise in the different projections. [ABSTRACT FROM AUTHOR]

The marine area of Northeast Greenland belongs to the largest national park in the world. Biodiversity assessments and tailored conservation measures often target specific physiographic or oceanographic features of an area for which detailed knowledge on their biological communities is incomplete. This study, therefore, characterizes epibenthic megafauna communities in a priori defined seabed habitats (fjord, shelf, shelf break and slope) and their relationship to environmental conditions in Northeast Greenland waters as a basis for conservation and management planning. Megabenthos was sampled from the Bessel Fjord across the shelf to the upper continental slope between latitudes 74.55°N–79.27°N and longitudes 5.22°W–21.72°W by Campelen and Agassiz trawls at 18 locations (total of 33 samples) at depths between 65 and 1011 m in August 2015 and September 2017. A total of 276 taxa were identified. Gross estimates of abundance ranged from 4 to 854 individuals 1000 m−2 and biomass ranged from 65 to 528 g wet weight 1000 m−2 (2017 only). The phyla Arthropoda and Porifera contributed the most to taxon richness, while Mollusca and Echinodermata were the most abundant, and Echinodermata had the highest biomass of all phyla. Fjord, shelf, shelf break and slope seabed habitats revealed different megafaunal communities that were partly explained by gradients in depth, bottom oxygen concentration, temperature, salinity, and turbidity. The present study provides a current baseline of megabenthos across seabed habitats in Northeast Greenlandic waters and reveals putative connections between Arctic and Atlantic biota. [ABSTRACT FROM AUTHOR]

The sensitivity of the climate system to changes in radiative forcing is crucial for our understanding of past and future climates. Especially important are feedbacks related to melting of ice sheets like the Greenland ice sheet (GIS) and its potential impact on the Atlantic meridional overturning circulation (AMOC). These effects are likely to delay and dampen predicted long-term warming trends. Estimates of climate sensitivity may be deduced from palaeoclimate-reconstructions, but this raises the question whether past climate sensitivity is applicable to the future. Therefore we have analysed the impact of GIS melt water on the AMOC strength in two past warm climates (last interglacial and early present interglacial) and three future scenarios with three different model parameter sets. These model parameter sets represent three different model sensitivities to freshwater perturbation: low, moderate and high. In both the moderate and high sensitivity versions, we find for lower GIS melt rates (below 54 mSv, Sv = 10 m/s) a clear difference between past and future warm climates in the sensitivity of the AMOC to GIS melt. This difference is connected to the convective activity in the Labrador Sea and the amount of additional surface freshening due to sea ice melting. In contrast, for higher GIS melt rates (over 54 mSv) we find similar reductions of the AMOC strength in all cases. Considering the low sensitivity version of our model, we find that for all GIS melt rates the influence of freshwater forcing on the AMOC is independent of the background climate. Our results and implications are thus strongly determined by the parameter set considered in our model. Nonetheless, our results from two out of three model versions suggest that proxy-based reconstructions of past AMOC sensitivity to GIS melt are likely to be misleading if interpreted for future applications. [ABSTRACT FROM AUTHOR]

The recent increase in the rate of the Greenland ice sheet melting has raised with urgency the question of the impact of such a melting on the climate. As former model projections, based on a coarse representation of the melting, show very different sensitivity to this melting, it seems necessary to consider a multi-model ensemble to tackle this question. Here we use five coupled climate models and one ocean-only model to evaluate the impact of 0.1 Sv (1 Sv = 10 m/s) of freshwater equally distributed around the coast of Greenland during the historical era 1965-2004. The ocean-only model helps to discriminate between oceanic and coupled responses. In this idealized framework, we find similar fingerprints in the fourth decade of hosing among the models, with a general weakening of the Atlantic Meridional Overturning Circulation (AMOC). Initially, the additional freshwater spreads along the main currents of the subpolar gyre. Part of the anomaly crosses the Atlantic eastward and enters into the Canary Current constituting a freshwater leakage tapping the subpolar gyre system. As a consequence, we show that the AMOC weakening is smaller if the leakage is larger. We argue that the magnitude of the freshwater leakage is related to the asymmetry between the subpolar-subtropical gyres in the control simulations, which may ultimately be a primary cause for the diversity of AMOC responses to the hosing in the multi-model ensemble. Another important fingerprint concerns a warming in the Nordic Seas in response to the re-emergence of Atlantic subsurface waters capped by the freshwater in the subpolar gyre. This subsurface heat anomaly reaches the Arctic where it emerges and induces a positive upper ocean salinity anomaly by introducing more Atlantic waters. We found similar climatic impacts in all the coupled ocean-atmosphere models with an atmospheric cooling of the North Atlantic except in the region around the Nordic Seas and a slight warming south of the equator in the Atlantic. This meridional gradient of temperature is associated with a southward shift of the tropical rains. The free surface models also show similar sea-level fingerprints notably with a comma-shape of high sea-level rise following the Canary Current. [ABSTRACT FROM AUTHOR]

Local sea level can deviate from mean global sea level because of both dynamic sea level (DSL) effects, resulting from oceanic and atmospheric circulation and temperature and salinity distributions, and changes in the static equilibrium (SE) sea level configuration, produced by the gravitational, elastic, and rotational effects of mass redistribution. Both effects will contribute to future sea level change. To compare their magnitude, we simulated the effects of Greenland Ice Sheet (GIS) melt by conducting idealized North Atlantic 'water-hosing' experiments in a climate model unidirectionally coupled to a SE sea level model. At current rates of GIS melt, we find that geographic SE patterns should be challenging but possible to detect above dynamic variability. At higher melt rates, we find that DSL trends are strongest in the western North Atlantic, while SE effects will dominate in most of the ocean when melt exceeds ~20 cm equivalent sea level. [ABSTRACT FROM AUTHOR]

Here we present a set of regional climate scenarios of sea level rise for the northeast Atlantic Ocean. In this study, the latest observations and results obtained with state-of-the-art climate models are combined. In addition, regional effects due to ocean dynamics and changes in the Earth’s gravity field induced by melting of land-based ice masses have been taken into account. The climate scenarios are constructed for the target years 2050 and 2100, for both a moderate and a large rise in global mean atmospheric temperature (2 °C and 4 °C in 2100 respectively). The climate scenarios contain contributions from changes in ocean density (global thermal expansion and local steric changes related to changing ocean dynamics) and changes in ocean mass (melting of mountain glaciers and ice caps, changes in the Greenland and Antarctic ice sheets, and (minor) terrestrial water-storage contributions). All major components depend on the global temperature rise achieved in the target periods considered. The resulting set of climate scenarios represents our best estimate of twenty-first century sea level rise in the northeast Atlantic Ocean, given the current understanding of the various contributions. For 2100, they yield a local rise of 30 to 55 cm and 40 to 80 cm for the moderate and large rise in global mean atmospheric temperature, respectively. [ABSTRACT FROM AUTHOR]

The dynamical adjustment process (DAP) is a requisite for climate system to arrange for a new equilibrium state. To evaluate the detailed structure of DAP during Heinrich Stadial (HS), high-resolution speleothem-based Asian summer monsoon (ASM) variability was reconstructed, separately covering HSs 5 to 1. In these calcite δ18O records, a gradual increase of ASM intensity is evident in each mid-HS, followed by a centennial-scale ASM stability lasting on average 590 years during late HS. At this time, δ18O values decrease by 1%, about 50% of the total HS, compared with maximum values in early HS. This structure of monsoonal HS in speleothem records is not reflected in temperature variations at the Greenland, but is well mirrored in middle- to low latitudes within the northern hemisphere, and even southern oceanic records. It suggests that southern and low-latitude climate conditions are likely important for the termination of HS. Thus, a DAP of about 400–600 years is a precondition for the ASM sub-system to prepare for a new equilibrium. [ABSTRACT FROM AUTHOR]