Spatial variations in the rate of sea level rise caused by the present-day melting of glaciers and ice sheets

Friction at the base of ice-sheets has been shown to be one of the largest uncertainty of model projections for the contribution of ice-sheet to future sea level rise. On hard beds, most of the apparent friction is the result of ice flowing over the bumps that have a size smaller than described by the grid resolution of ice-sheet models. To account for this friction, the classical approach is to replace this under resolved roughness by an ad-hoc friction law. In an imaginary world of unlimited computing resource and highly resolved bedrock DEM, one should solve for all bed roughnesses assuming pure sliding at the bedrock-ice interface. If such solutions are not affordable at the scale of an ice-sheet or even at the scale of a glacier, the effect of small bumps can be inferred using synthetical periodic geometry. In this presentation,&#160; beds are constructed using the superposition of up to five bed geometries made of sinusoidal bumps of decreasing wavelength and amplitudes. The contribution to the total friction of all five beds is evaluated by inverse methods using the most resolved solution as observation. It is shown that small features of few meters can contribute up to almost half of the total friction, depending on the wavelengths and amplitudes distribution. This work also confirms that the basal friction inferred using inverse method&#160; is very sensitive to how the bed topography is described by the model grid, and therefore depends on the size of the model grid itself.&#160;

Download Full-text

Ice Sheets and Sea-Level Rise in Earth System Models

10.2172/1156833 ◽

2014 ◽

Author(s):

Stephen Price

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheets ◽

Earth System ◽

System Models ◽

Earth System Models ◽

And Sea Level

Download Full-text

Brief communication: On calculating the sea-level contribution in marine ice-sheet models

The Cryosphere ◽

10.5194/tc-14-833-2020 ◽

2020 ◽

Vol 14 (3) ◽

pp. 833-840 ◽

Cited By ~ 3

Author(s):

Heiko Goelzer ◽

Violaine Coulon ◽

Frank Pattyn ◽

Bas de Boer ◽

Roderik van de Wal

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

Ocean Water ◽

Ice Volume ◽

Isostatic Adjustment ◽

The Common

Abstract. Estimating the contribution of marine ice sheets to sea-level rise is complicated by ice grounded below sea level that is replaced by ocean water when melted. The common approach is to only consider the ice volume above floatation, defined as the volume of ice to be removed from an ice column to become afloat. With isostatic adjustment of the bedrock and external sea-level forcing that is not a result of mass changes of the ice sheet under consideration, this approach breaks down, because ice volume above floatation can be modified without actual changes in the sea-level contribution. We discuss a consistent and generalised approach for estimating the sea-level contribution from marine ice sheets.

Download Full-text

ISMIP6 Future Projections for Antarctica performed using the AWI PISM ice sheet model

10.5194/egusphere-egu2020-16948 ◽

2020 ◽

Author(s):

Thomas Kleiner ◽

Jeremie Schmiedel ◽

Angelika Humbert

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Climate Models ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Shelf ◽

Initial State ◽

Intercomparison Project ◽

Non Local ◽

The Impact

Ice sheets constitute the largest and most uncertain potential source of future sea-level rise. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) brings together a consortium of international ice sheet and climate models to explore the contribution from the Greenland and Antarctic ice sheets to future sea-level rise. We use the Parallel Ice Sheet Model (PISM, pism-docs.org) to carry out spinup and projection simulations for the Antarctic Ice Sheet. Our treatment of the ice-ocean boundary condition previously based on 3D ocean temperatures (initMIP-Antarctica) has been adopted to use the ISMIP6 parameterisation and 3D ocean forcing fields (temperature and salinity) according to the ISMIP6 protocol. In this study, we analyse the impact of the choices made during the model initialisation procedure on the initial state. We present the AWI PISM results of the ISMIP6 projection simulations and investigate the ice sheet response for individual basins. In the analysis, we distinguish between the local and non-local ice shelf basal melt parameterisation.

Download Full-text

Trends and projections in ice sheet mass balance

10.5194/egusphere-egu2020-20660 ◽

2020 ◽

Author(s):

Andrew Shepherd ◽

Keyword(s):

Mass Balance ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ice Dynamics ◽

Surface Mass ◽

Sea Levels ◽

Global Sea Level

In recent decades, the Antarctic and Greenland Ice Sheets have been major contributors to global sea-level rise and are expected to be so in the future. Although increases in glacier flow and surface melting have been driven by oceanic and atmospheric warming, the degree and trajectory of today&#8217;s imbalance remain uncertain. Here we compare and combine 26 individual satellite records of changes in polar ice sheet volume, flow and gravitational potential to produce a reconciled estimate of their mass balance. Since the early 1990&#8217;s, ice losses from Antarctica and Greenland have caused global sea-levels to rise by 18.4 millimetres, on average, and there has been a sixfold increase in the volume of ice loss over time. Of this total, 41 % (7.6 millimetres) originates from Antarctica and 59 % (10.8 millimetres) is from Greenland. In this presentation, we compare our reconciled estimates of Antarctic and Greenland ice sheet mass change to IPCC projection of sea level rise to assess the model skill in predicting changes in ice dynamics and surface mass balance. &#160;Cumulative ice losses from both ice sheets have been close to the IPCC&#8217;s predicted rates for their high-end climate warming scenario, which forecast an additional 170 millimetres of global sea-level rise by 2100 when compared to their central estimate.

Download Full-text

Sea-level rise and its possible impacts given a ‘beyond 4°C world’ in the twenty-first century

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2010.0291 ◽

2011 ◽

Vol 369 (1934) ◽

pp. 161-181 ◽

Cited By ~ 296

Author(s):

Robert J. Nicholls ◽

Natasha Marinova ◽

Jason A. Lowe ◽

Sally Brown ◽

Pier Vellinga ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Temperature Rise ◽

Full Range ◽

Ice Sheets ◽

Time Frame ◽

First Century ◽

Climate Mitigation ◽

Twenty First Century ◽

The Impact

The range of future climate-induced sea-level rise remains highly uncertain with continued concern that large increases in the twenty-first century cannot be ruled out. The biggest source of uncertainty is the response of the large ice sheets of Greenland and west Antarctica. Based on our analysis, a pragmatic estimate of sea-level rise by 2100, for a temperature rise of 4°C or more over the same time frame, is between 0.5 m and 2 m—the probability of rises at the high end is judged to be very low, but of unquantifiable probability. However, if realized, an indicative analysis shows that the impact potential is severe, with the real risk of the forced displacement of up to 187 million people over the century (up to 2.4% of global population). This is potentially avoidable by widespread upgrade of protection, albeit rather costly with up to 0.02 per cent of global domestic product needed, and much higher in certain nations. The likelihood of protection being successfully implemented varies between regions, and is lowest in small islands, Africa and parts of Asia, and hence these regions are the most likely to see coastal abandonment. To respond to these challenges, a multi-track approach is required, which would also be appropriate if a temperature rise of less than 4°C was expected. Firstly, we should monitor sea level to detect any significant accelerations in the rate of rise in a timely manner. Secondly, we need to improve our understanding of the climate-induced processes that could contribute to rapid sea-level rise, especially the role of the two major ice sheets, to produce better models that quantify the likely future rise more precisely. Finally, responses need to be carefully considered via a combination of climate mitigation to reduce the rise and adaptation for the residual rise in sea level. In particular, long-term strategic adaptation plans for the full range of possible sea-level rise (and other change) need to be widely developed.

Download Full-text

Ice sheet mass balance and sea level

Antarctic Science ◽

10.1017/s0954102009990137 ◽

2009 ◽

Vol 21 (5) ◽

pp. 413-426 ◽

Cited By ~ 58

Author(s):

I. Allison ◽

R.B. Alley ◽

H.A. Fricker ◽

R.H. Thomas ◽

R.C. Warner

Keyword(s):

Mass Balance ◽

Sea Level Rise ◽

Sea Level ◽

Average Rate ◽

Ice Sheets ◽

Ice Sheet ◽

Measurement Technology ◽

Satellite Gravity ◽

Intergovernmental Panel ◽

Ice Sheet Mass Balance

AbstractDetermining the mass balance of the Greenland and Antarctic ice sheets (GIS and AIS) has long been a major challenge for polar science. But until recent advances in measurement technology, the uncertainty in ice sheet mass balance estimates was greater than any net contribution to sea level change. The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (AR4) was able, for the first time, to conclude that, taken together, the GIS and AIS have probably been contributing to sea level rise over the period 1993–2003 at an average rate estimated at 0.4 mm yr-1. Since the cut-off date for work included in AR4, a number of further studies of the mass balance of GIS and AIS have been made using satellite altimetry, satellite gravity measurements and estimates of mass influx and discharge using a variety of techniques. Overall, these studies reinforce the conclusion that the ice sheets are contributing to present sea level rise, and suggest that the rate of loss from GIS has recently increased. The largest unknown in the projections of sea level rise over the next century is the potential for rapid dynamic collapse of ice sheets.

Download Full-text

A scaling approach to project regional sea level rise and its uncertainties

Earth System Dynamics ◽

10.5194/esd-4-11-2013 ◽

2013 ◽

Vol 4 (1) ◽

pp. 11-29 ◽

Cited By ~ 77

Author(s):

M. Perrette ◽

F. Landerer ◽

R. Riva ◽

K. Frieler ◽

M. Meinshausen

Keyword(s):

Climate Change ◽

Sea Level Rise ◽

Sea Level ◽

General Circulation ◽

Ice Sheets ◽

General Circulation Models ◽

Ice Melt ◽

Probabilistic Forecasts ◽

Regional Sea Level ◽

Global Mean

Abstract. Climate change causes global mean sea level to rise due to thermal expansion of seawater and loss of land ice from mountain glaciers, ice caps and ice sheets. Locally, sea level can strongly deviate from the global mean rise due to changes in wind and ocean currents. In addition, gravitational adjustments redistribute seawater away from shrinking ice masses. However, the land ice contribution to sea level rise (SLR) remains very challenging to model, and comprehensive regional sea level projections, which include appropriate gravitational adjustments, are still a nascent field (Katsman et al., 2011; Slangen et al., 2011). Here, we present an alternative approach to derive regional sea level changes for a range of emission and land ice melt scenarios, combining probabilistic forecasts of a simple climate model (MAGICC6) with the new CMIP5 general circulation models. The contribution from ice sheets varies considerably depending on the assumptions for the ice sheet projections, and thus represents sizeable uncertainties for future sea level rise. However, several consistent and robust patterns emerge from our analysis: at low latitudes, especially in the Indian Ocean and Western Pacific, sea level will likely rise more than the global mean (mostly by 10–20%). Around the northeastern Atlantic and the northeastern Pacific coasts, sea level will rise less than the global average or, in some rare cases, even fall. In the northwestern Atlantic, along the American coast, a strong dynamic sea level rise is counteracted by gravitational depression due to Greenland ice melt; whether sea level will be above- or below-average will depend on the relative contribution of these two factors. Our regional sea level projections and the diagnosed uncertainties provide an improved basis for coastal impact analysis and infrastructure planning for adaptation to climate change.

Download Full-text

Increased West Antarctic ice discharge and East Antarctic stability over the last seven years

10.5194/tc-2017-75 ◽

2017 ◽

Cited By ~ 1

Author(s):

Alex S. Gardner ◽

Geir Moholdt ◽

Ted Scambos ◽

Mark Fahnstock ◽

Stefan Ligtenberg ◽

...

Keyword(s):

Synthetic Aperture Radar ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheets ◽

Synthetic Aperture ◽

Direct Role ◽

Ice Flow ◽

West Antarctic ◽

Landsat 7 ◽

Ice Velocity

Abstract. Ice discharge from large ice sheets plays a direct role in determining rates of sea level rise. We map present-day Antarctic-wide surface velocities using Landsat 7 & 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 with a mean error of

Download Full-text

Asynchronous Antarctic and Greenland ice-volume contributions to the last interglacial sea-level highstand

10.5194/egusphere-egu2020-1513 ◽

2020 ◽

Author(s):

Eelco Rohling ◽

Fiona Hibbert

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Global Climate ◽

Ice Sheets ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Climate Forcing ◽

Potential Contribution ◽

Last Interglacial ◽

Ice Shelf

Sea-level rise is among the greatest risks that arise from anthropogenic global climate change. It is receiving a lot of attention, among others in the IPCC reports, but major questions remain as to the potential contribution from the great continental ice sheets. In recent years, some modelling work has suggested that the ice-component of sea-level rise may be much faster than previously thought, but the rapidity of rise seen in these results depends on inclusion of scientifically debated mechanisms of ice-shelf decay and associated ice-sheet instability. The processes have not been active during historical times, so data are needed from previous warm periods to evaluate whether the suggested rates of sea-level rise are supported by observations or not. Also, we then need to assess which of the ice sheets was most sensitive, and why. The last interglacial (LIG; ~130,000 to ~118,000 years ago, ka) was the last time global sea level rose well above its present level, reaching a highstand of +6 to +9 m or more. Because Greenland Ice Sheet (GrIS) contributions were smaller than that, this implies substantial Antarctic Ice Sheet (AIS) contributions. However, this still leaves the timings, magnitudes, and drivers of GrIS and AIS reductions open to debate. I will discuss recently published sea-level reconstructions for the LIG highstand, which reveal that AIS and GrIS contributions were distinctly asynchronous, and that rates of rise to values above 0 m (present-day sea level) reached up to 3.5 m per century. Such high pre-anthropogenic rates of sea-level rise lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations, for both the past and future. Climate forcing was distinctly asynchronous between the southern and northern hemispheres as well during the LIG, explaining the asynchronous sea-level contributions from AIS and GrIS. Today, climate forcing is synchronous between the two hemispheres, and also faster and greater than during the LIG. Therefore, LIG rates of sea-level rise should likely be considered minimum estimates for the future.

Download Full-text