Accelerated West Antarctic ice mass loss continues to outpace East Antarctic gains

Harig, C.; Simons, Frederik J.

doi:10.1016/j.epsl.2015.01.029

Cited by 104 publications

(87 citation statements)

References 77 publications

(103 reference statements)

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“…Because the SMB of the ice sheet has not shown a significant trend in the past (33, 34), we assume total mass changes to be a proxy for the changes in SID. We use three observational datasets for Antarctic mass loss (26,39,40) (Fig. 1E) in all three cases.…”

Section: Resultsmentioning

confidence: 99%

Future sea level rise constrained by observations and long-term commitment

Mengel

Levermann

Frieler

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

182

169

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Sea level has been steadily rising over the past century, predominantly due to anthropogenic climate change. The rate of sea level rise will keep increasing with continued global warming, and, even if temperatures are stabilized through the phasing out of greenhouse gas emissions, sea level is still expected to rise for centuries. This will affect coastal areas worldwide, and robust projections are needed to assess mitigation options and guide adaptation measures. Here we combine the equilibrium response of the main sea level rise contributions with their last century's observed contribution to constrain projections of future sea level rise. Our model is calibrated to a set of observations for each contribution, and the observational and climate uncertainties are combined to produce uncertainty ranges for 21st century sea level rise. We project anthropogenic sea level rise of 28-56 cm, 37-77 cm, and 57-131 cm in 2100 for the greenhouse gas concentration scenarios RCP26, RCP45, and RCP85, respectively. Our uncertainty ranges for total sea level rise overlap with the process-based estimates of the Intergovernmental Panel on Climate Change. The "constrained extrapolation" approach generalizes earlier global semiempirical models and may therefore lead to a better understanding of the discrepancies with processbased projections. 2) with a rate of around 3 cm per decade since 1990 (3, 4). Thermal expansion of the oceans and retreating glaciers are the main contributors to sea level rise in the past century and the near future. On multicentennial timescales, the Greenland and Antarctic ice sheets will likely dominate global sea level rise (5). Future sea level rise will pose challenges to coastal regions around the globe, and robust projections are needed to guide adaptation investment and provide incentives for climate mitigation (6).Projecting sea level relies on the understanding of the processes that drive sea level changes and on reliable data to verify and calibrate models. So-called process-based models now deliver projections for the main components of climate-driven sea level rise-thermal expansion, glaciers and ice caps, the Greenland ice sheet, and the Antarctic ice sheet-although solid ice discharge (SID) from the ice sheets is still difficult to constrain (3). Semiempirical models follow a different approach and use the statistical relation between global mean temperature (7,8) or radiative forcing (9, 10) and sea level from past observations. Without aiming to capture the full physics of the sea level components, they project future sea level assuming that the past statistical relation also holds in the future. Their simpler nature makes them feasible for probabilistic assessments and makes their results easier to reproduce.The long-term multicentennial to millennial sensitivity of the main individual sea level contributors to global temperature changes can be constrained by paleoclimatic data and is more easily computed with currently available process-based large-scale models than are decadal to centenn...

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Section: Resultsmentioning

confidence: 99%

Future sea level rise constrained by observations and long-term commitment

Mengel

Levermann

Frieler

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

182

169

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“…Dronning Maud Land in East Antarctica experienced a mass gain accounting for a fall in GMSL of 0.17±0.02 mm year −1 since 2008 [74]. Harig and Simons [75] used techniques to increase the spatial resolution of the GRACE data, thus better resolving regional variations, and arrived at similar estimates. As noted above, Wouters et al [70] and Wu and Helfin (2015) cautioned that these calculated accelerations are for short periods and are affected by longerterm climate variability.…”

Section: Antarctic Ice Sheetmentioning

confidence: 88%

Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change

Clark

Church

Gregory

et al. 2015

Curr Clim Change Rep

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Considerable progress has been made in understanding the present and future regional and global sea level in the 2 years since the publication of the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change. Here, we evaluate how the new results affect the AR5's assessment of (i) historical sea level rise, including attribution of that rise and implications for the sea level budget, (ii) projections of the components and of total global mean sea level (GMSL), and (iii) projections of regional variability and emergence of the anthropogenic signal. In each of these cases, new work largely provides additional evidence in support of the AR5 assessment, providing greater confidence in those findings. Recent analyses confirm the twentieth century sea level rise, with some analyses showing a slightly smaller rate before 1990 and some a slightly larger value than reported in the AR5. There is now more evidence of an acceleration in the rate of rise. Ongoing ocean heat uptake and associated thermal expansion have continued since 2000, and are consistent with ocean thermal expansion reported in the AR5. A significant amount of heat is being stored deeper in the water column, with a larger rate of heat uptake since 2000 compared to the previous decades and with the largest storage in the Southern Ocean. The first formal detection studies for ocean thermal expansion and glacier mass loss since the AR5 have confirmed the AR5 finding of a significant anthropogenic contribution to sea level rise over the last 50 years. New projections of glacier loss from two regions suggest smaller contributions to GMSL rise from these regions than in studies assessed by the AR5; additional regional studies are required to further assess whether there are broader implications of these results. Mass loss from the Greenland Ice Sheet, primarily as a result of increased surface melting, and from the Antarctic Ice Sheet, primarily as a result of increased ice discharge, has accelerated. The largest estimates of acceleration in mass loss from the two ice sheets for 2003-2013 equal or exceed the acceleration of GMSL rise calculated from the satellite altimeter sea level record over the longer period of 1993-2014. However, when increased mass gain in land water storage and parts of East Antarctica, and decreased mass loss from glaciers in Alaska and some other regions are taken into account, the net acceleration in the ocean mass gain is consistent with the satellite altimeter record. New studies suggest that a marine ice sheet instability (MISI) may have been initiated in parts of the West Antarctic Ice Sheet (WAIS), but that it will affect only a limited number of ice streams in the twenty-first century. New projections of mass loss from the Greenland and Antarctic Ice Sheets by 2100, including a contribution from parts of WAIS undergoing unstable retreat, suggest a contribution that falls largely within the likely range (i.e., two thirds probability) of the AR5. These new results increase confidence in the AR5 likel...

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“…For the whole of Antarctica, we estimate an average mass budget of −183 ± 94 Gt yr −1 for the 2008-2015 period. Other recent estimates of Antarctic mass change include those derived from CryoSat-2 altimetry of −159 ± 48 Gt yr −1 for the period 2010(McMillan et al, 2014 and −116 ± 76 Gt yr −1 for the period (Helm et al, 2014, assuming density of ice) and a recent estimate from the joint inversion of gravity, altimetry and GPS data of −159 ± 22 Gt yr −1 for the period 2010(Martín-Español et al, 2016. All three studies show near balance to slightly positive mass changes for the East Antarctic Ice Sheet and large losses for the West Antarctic Ice Sheet and the Antarctic Peninsula, all of which agree well with the results presented here when considering uncertainties and differences in study periods.…”

Section: Changes In Net Mass Balancementioning

confidence: 99%

“…Recent studies indicate significant mass loss from the Antarctic ice sheet that is likely accelerating (Harig and Simons, 2015;Helm et al, 2014;Martín-Español et al, 2016;McMillan et al, 2014;Rignot et al, 2011b;Shepherd et al, 2012;Velicogna, 2009). Understanding how this imbalance evolves is critical to providing meaningful projections of sea-level change.…”

Section: Introductionmentioning

confidence: 99%

Increased West Antarctic and unchanged East Antarctic ice discharge over the last 7 years

Gardner

Moholdt

Scambos³

et al. 2018

The Cryosphere

412

495

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Abstract. Ice discharge from large ice sheets plays a direct role in determining rates of sea-level rise. We map presentday Antarctic-wide surface velocities using Landsat 7 and 8 imagery spanning 2013-2015 and compare to earlier estimates derived from synthetic aperture radar, revealing heterogeneous changes in ice flow since ∼ 2008. The new mapping provides complete coastal and inland coverage of ice velocity north of 82.4 • S with a mean error of < 10 m yr −1 , resulting from multiple overlapping image pairs acquired during the daylight period. Using an optimized flux gate, ice discharge from Antarctica is 1929 ± 40 Gigatons per year (Gt yr −1 ) in 2015, an increase of 36 ± 15 Gt yr −1 from the time of the radar mapping. Flow accelerations across the grounding lines of West Antarctica's Amundsen Sea Embayment, Getz Ice Shelf and Marguerite Bay on the western Antarctic Peninsula, account for 88 % of this increase. In contrast, glaciers draining the East Antarctic Ice Sheet have been remarkably constant over the period of observation. Including modeled rates of snow accumulation and basal melt, the Antarctic ice sheet lost ice at an average rate of 183 ± 94 Gt yr −1 between 2008 and 2015. The modest increase in ice discharge over the past 7 years is contrasted by high rates of ice sheet mass loss and distinct spatial patters of elevation lowering. The West Antarctic Ice Sheet is experiencing high rates of mass loss and displays distinct patterns of elevation lowering that point to a dynamic imbalance. We find modest increase in ice discharge over the past 7 years, which suggests that the recent pattern of mass loss in Antarctica is part of a longer-term phase of enhanced glacier flow initiated in the decades leading up to the first continent-wide radar mapping of ice flow.

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Accelerated West Antarctic ice mass loss continues to outpace East Antarctic gains

Cited by 104 publications

References 77 publications

Future sea level rise constrained by observations and long-term commitment

Future sea level rise constrained by observations and long-term commitment

Recent Progress in Understanding and Projecting Regional and Global Mean Sea Level Change

Increased West Antarctic and unchanged East Antarctic ice discharge over the last 7 years

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