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"Greenland"
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Overshooting the critical threshold for the Greenland ice sheet
Melting of the Greenland ice sheet (GrIS) in response to anthropogenic global warming poses a severe threat in terms of global sea-level rise (SLR)
1
. Modelling and palaeoclimate evidence suggest that rapidly increasing temperatures in the Arctic can trigger positive feedback mechanisms for the GrIS, leading to self-sustained melting
2
–
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, and the GrIS has been shown to permit several stable states
5
. Critical transitions are expected when the global mean temperature (GMT) crosses specific thresholds, with substantial hysteresis between the stable states
6
. Here we use two independent ice-sheet models to investigate the impact of different overshoot scenarios with varying peak and convergence temperatures for a broad range of warming and subsequent cooling rates. Our results show that the maximum GMT and the time span of overshooting given GMT targets are critical in determining GrIS stability. We find a threshold GMT between 1.7 °C and 2.3 °C above preindustrial levels for an abrupt ice-sheet loss. GrIS loss can be substantially mitigated, even for maximum GMTs of 6 °C or more above preindustrial levels, if the GMT is subsequently reduced to less than 1.5 °C above preindustrial levels within a few centuries. However, our results also show that even temporarily overshooting the temperature threshold, without a transition to a new ice-sheet state, still leads to a peak in SLR of up to several metres.
Simulations using two state-of-the-art ice-sheet models show that abrupt melting of the Greenland ice sheet following overshooting of the global mean temperature critical threshold can be mitigated by subsequent cooling to below 1.5 °C.
Journal Article
Greenland
An introduction to the country of Greenland, including its geography, history, and traditions and customs.
Book
The Greenland Entomofauna
The Greenland Entomofauna provides a richly illustrated tool for the identification of the insects, spiders, mites etc. of the country, hence enabling detailed future monitoring of range shifts of individual species.
eBook
Diversification inside a lamprophyric dyke and cone sheet complex converging onto a hidden carbonatite centre (Frederikshåbs Isblink, SW Greenland)
Both radiating dykes and proximal cone sheets converge onto a positive aeromagnetic anomaly of an inferred carbonatitic centre, hidden beneath a retreating edge of the Frederikshåbs Isblink glacier. This convergence, together with sub-parallel incompatible element patterns by all intrusions, suggests a cogenetic relationship that warrants investigation into potential diversification processes. More primitive high- and low-Mg damtjernites, which for three dykes conform to more porphyritic dyke cores and aphyric margins, respectively, can be explained by high-Mg trends being controlled by the fractionation/accumulation of mainly augite and olivine (or other mafic phases), while discordant low-Mg trends require additional decoupled magnetite fractionation. It is proposed that each dyke intrusion tapped the differentiated top of a central magma chamber, occasionally followed by an unconsolidated mafic cumulate mush, excluding denser magnetites, with in situ flow segregation playing a subordinate additional role. Beyond the most differentiated damtjernite, more evolved phonolitic nephelinites to carbonaceous alnöites split into bulk rock geochemical T-trends that can only relate to late-stage segregations into magmas with varying proportions of interstitial igneous (not secondary) analcime and carbonate – collectively increasing in volume with differentiation. While the analcime component also appears to segregate more readily into veins and ocelli than carbonatite, it is speculated if such low viscosity, density and liquidus rest melts, inside igneous centres, more efficiently aggregated into voluminous, buoyant analcime caps above slightly denser carbonatites. Similar converging plumbing systems and diversification processes are proposed for other complexes, where kimberlitic parents were simply extracted from deeper mantle sources.
Journal Article
A realistic Greenland ice sheet and surrounding glaciers and ice caps melting in a coupled climate model
Greenland ice sheet experienced an intensive melting in the last century, especially in the 1920s and over the last decades. The supplementary input into the ocean could disrupt the freshwater budget of the North Atlantic. Simultaneously, some signs of a recent weakening of the Atlantic Meridional Overturning Circulation (AMOC) have been reported. In order to better understand the possible impact of the increasing melting on the North Atlantic circulation, salinity and temperature trends, we construct an observation-based estimate of the freshwater fluxes spanning from 1840 to 2014. The estimate is based on runoff fluxes coming from Greenland ice sheet and surrounding glaciers and ice caps. Input from iceberg melting is also included and spatially distributed over the North Atlantic following an observed climatology. We force a set of historical simulations of the IPSL-CM6A-LR coupled climate model with this reconstruction from 1920 to 2014. The ten-member ensemble mean displays freshened and cooled waters around Greenland, which spread in the subpolar gyre, and then towards the subtropical gyre and the Nordic Seas. Over the whole period, the convection is reduced in the Labrador and Nordic Seas, while it is slightly enhanced in the Irminger Sea, and the AMOC is weakened by
0.32
±
0.35
Sv at
26
∘
N. The multi-decadal trend of the North Atlantic surface temperature obtained with the additional freshwater forcing is slightly closer to observations than in standard historical simulations, although the two trends are only different at the 90% confidence level. Slight improvement of the Root Mean Square Error with respect to observations in the subpolar gyre region suggests that part of the surface temperature variability over the recent decades may have been forced by the release of freshwater from Greenland and surrounding regions since the 1920s. Finally, we highlight that the AMOC decrease due to Greenland melting remains modest in these simulations and can only explain a very small amount of the
3
±
1
Sv weakening suggested in a recent study.
Journal Article
The causes of sea-level rise since 1900
The rate of global-mean sea-level rise since 1900 has varied over time, but the contributing factors are still poorly understood
1
. Previous assessments found that the summed contributions of ice-mass loss, terrestrial water storage and thermal expansion of the ocean could not be reconciled with observed changes in global-mean sea level, implying that changes in sea level or some contributions to those changes were poorly constrained
2
,
3
. Recent improvements to observational data, our understanding of the main contributing processes to sea-level change and methods for estimating the individual contributions, mean another attempt at reconciliation is warranted. Here we present a probabilistic framework to reconstruct sea level since 1900 using independent observations and their inherent uncertainties. The sum of the contributions to sea-level change from thermal expansion of the ocean, ice-mass loss and changes in terrestrial water storage is consistent with the trends and multidecadal variability in observed sea level on both global and basin scales, which we reconstruct from tide-gauge records. Ice-mass loss—predominantly from glaciers—has caused twice as much sea-level rise since 1900 as has thermal expansion. Mass loss from glaciers and the Greenland Ice Sheet explains the high rates of global sea-level rise during the 1940s, while a sharp increase in water impoundment by artificial reservoirs is the main cause of the lower-than-average rates during the 1970s. The acceleration in sea-level rise since the 1970s is caused by the combination of thermal expansion of the ocean and increased ice-mass loss from Greenland. Our results reconcile the magnitude of observed global-mean sea-level rise since 1900 with estimates based on the underlying processes, implying that no additional processes are required to explain the observed changes in sea level since 1900.
Observed global-mean sea-level rise since 1900 is reconciled with estimates based on the contributing processes, revealing budget closure within uncertainties and showing ice-mass loss from glaciers as a dominant contributor.
Journal Article