The Paris agreement aims to hold global warming to well below 2 ∘C and
to pursue efforts to limit it to 1.5 ∘C relative to the pre-industrial
period. Recent estimates based on population growth and ...intended carbon
emissions from participant countries suggest global warming may exceed this
ambitious target. Here we present glacier volume projections for the end of
this century, under a range of high-end climate change scenarios, defined as
exceeding +2 ∘C global average warming relative to the pre-industrial
period. Glacier volume is modelled by developing an elevation-dependent mass
balance model for the Joint UK Land Environment Simulator (JULES). To do
this, we modify JULES to include glaciated and unglaciated surfaces that
can exist at multiple heights within a single grid box. Present-day mass
balance is calibrated by tuning albedo, wind speed, precipitation, and
temperature lapse rates to obtain the best agreement with observed mass
balance profiles. JULES is forced with an ensemble of six Coupled Model
Intercomparison Project Phase 5 (CMIP5) models, which were downscaled using
the high-resolution HadGEM3-A atmosphere-only global climate model. The
CMIP5 models use the RCP8.5 climate change scenario and were selected on the
criteria of passing 2 ∘C global average warming during this century. The
ensemble mean volume loss at the end of the century plus or minus 1 standard
deviation is -64±5 % for all glaciers excluding those on the
peripheral of the Antarctic ice sheet. The uncertainty in the multi-model
mean is rather small and caused by the sensitivity of HadGEM3-A to the
boundary conditions supplied by the CMIP5 models. The regions which lose
more than 75 % of their initial volume by the end of the century are
Alaska, western Canada and the US, Iceland, Scandinavia, the Russian Arctic, central
Europe, Caucasus, high-mountain Asia, low latitudes, southern Andes, and New
Zealand. The ensemble mean ice loss expressed in sea level equivalent
contribution is 215.2±21.3 mm. The largest contributors to sea level
rise are Alaska (44.6±1.1 mm), Arctic Canada north and south (34.9±3.0 mm), the Russian Arctic (33.3±4.8 mm), Greenland (20.1±4.4), high-mountain Asia (combined central Asia, South Asia east and west),
(18.0±0.8 mm), southern Andes (14.4±0.1 mm), and Svalbard (17.0±4.6 mm). Including parametric uncertainty in the calibrated mass
balance parameters gives an upper bound global volume loss of 281.1 mm
of sea level equivalent by the end of the century. Such large ice losses will
have inevitable consequences for sea level rise and for water supply in
glacier-fed river systems.
Estimates of glacial sediment delivery to the oceans have been derived from fluxes of meltwater runoff and iceberg calving, and their sediment loads. The combined total (2900
Tg
yr
−1) of the ...suspended sediment load in meltwaters (1400
Tg
yr
−1) and the sediment delivered by icebergs (1500
Tg
yr
−1) are within the range of earlier estimates. High-resolution microscopic observations show that suspended sediments from glacial meltwaters, supraglacial, and proglacial sediments, and sediments in basal ice, from Arctic, Alpine, and Antarctic locations all contain iron (oxyhydr)oxide nanoparticles, which are poorly crystalline, typically ∼5
nm in diameter, and which occur as single grains or aggregates that may be isolated or attached to sediment grains. Nanoparticles with these characteristics are potentially bioavailable. A global model comparing the sources and sinks of iron present as (oxyhydr)oxides indicates that sediment delivered by icebergs is a significant source of iron to the open oceans, beyond the continental shelf. Iceberg delivery of sediment containing iron as (oxyhydr)oxides during the Last Glacial Maximum may have been sufficient to fertilise the increase in oceanic productivity required to drawdown atmospheric CO
2 to the levels observed in ice cores.
The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with ...modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). Over this period, ocean-driven melting has caused rates of ice loss from West Antarctica to increase from 53 ± 29 billion to 159 ± 26 billion tonnes per year; ice-shelf collapse has increased the rate of ice loss from the Antarctic Peninsula from 7 ± 13 billion to 33 ± 16 billion tonnes per year. We find large variations in and among model estimates of surface mass balance and glacial isostatic adjustment for East Antarctica, with its average rate of mass gain over the period 1992-2017 (5 ± 46 billion tonnes per year) being the least certain.
The Greenland Ice Sheet has been a major contributor to global sea-level rise in recent decades
, and it is expected to continue to be so
. Although increases in glacier flow
and surface melting
have ...been driven by oceanic
and atmospheric
warming, the magnitude and trajectory of the ice sheet's mass imbalance remain uncertain. Here we compare and combine 26 individual satellite measurements of changes in the ice sheet's volume, flow and gravitational potential to produce a reconciled estimate of its mass balance. The ice sheet was close to a state of balance in the 1990s, but annual losses have risen since then, peaking at 345 ± 66 billion tonnes per year in 2011. In all, Greenland lost 3,902 ± 342 billion tonnes of ice between 1992 and 2018, causing the mean sea level to rise by 10.8 ± 0.9 millimetres. Using three regional climate models, we show that the reduced surface mass balance has driven 1,964 ± 565 billion tonnes (50.3 per cent) of the ice loss owing to increased meltwater runoff. The remaining 1,938 ± 541 billion tonnes (49.7 per cent) of ice loss was due to increased glacier dynamical imbalance, which rose from 46 ± 37 billion tonnes per year in the 1990s to 87 ± 25 billion tonnes per year since then. The total rate of ice loss slowed to 222 ± 30 billion tonnes per year between 2013 and 2017, on average, as atmospheric circulation favoured cooler conditions
and ocean temperatures fell at the terminus of Jakobshavn Isbræ
. Cumulative ice losses from Greenland as a whole have been close to the rates predicted by the Intergovernmental Panel on Climate Change for their high-end climate warming scenario
, which forecast an additional 70 to 130 millimetres of global sea-level rise by 2100 compared with their central estimate.
Reducing the uncertainty in the past, present and future contribution of ice sheets to sea-level change requires a coordinated effort between the climate and glaciology communities. The Ice Sheet ...Model Intercomparison Project for CMIP6 (ISMIP6) is the primary activity within the Coupled Model Intercomparison Project - phase 6 (CMIP6) focusing on the Greenland and Antarctic Ice Sheets. In this paper, we describe the framework for ISMIP6 and its relationship to other activities within CMIP6. The ISMIP6 experimental design relies on CMIP6 climate models and includes, for the first time within CMIP, coupled ice sheet - climate models as well as standalone ice sheet models. To facilitate analysis of the multi-model ensemble and to generate a set of standard climate inputs for standalone ice sheet models, ISMIP6 defines a protocol for all variables related to ice sheets. ISMIP6 will provide a basis for investigating the feedbacks, impacts, and sea-level changes associated with dynamic ice sheets and for quantifying the uncertainty in ice-sheet-sourced global sea-level change.
Larsen Ice Shelf Has Progressively Thinned Shepherd, Andrew; Wingham, Duncan; Payne, Tony ...
Science (American Association for the Advancement of Science),
10/2003, Volume:
302, Issue:
5646
Journal Article
Peer reviewed
The retreat and collapse of Antarctic Peninsula ice shelves in tandem with a regional atmospheric warming has fueled speculation as to how these events may be related. Satellite radar altimeter ...measurements show that between 1992 and 2001 the Larsen Ice Shelf lowered by up to 0.27 ± 0.11 meters per year. The lowering is explained by increased summer melt-water and the loss of basal ice through melting. Enhanced ocean-driven melting may provide a simple link between regional climate warming and the successive disintegration of sections of the Larsen Ice Shelf.
The cryosphere comprises all the frozen water and soil on the surface of the Earth. Mass Balance of the Cryosphere focuses on two key components of this environment: land ice (in the form of ice ...sheets, caps and glaciers) and sea ice. These components have been identified as important indicators of both short and long term climate change. Early chapters cover the theory behind field-based and satellite observations, and modelling of mass balance, providing a thorough grounding in all the concepts and issues presented later in the book. Later chapters review our current understanding of the present and predicted future mass balance of the cryosphere. This is an important reference for all scientists working in the fields of climate change, environmental sciences and glaciology. It is written by leading authors in the field, and is fully integrated to provide a coherent, cross-referenced and consistent exposition on the subject.
Preface Payne, Tony
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
07/2006, Volume:
364, Issue:
1844
Journal Article
Preface Payne, Tony
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
07/2006, Volume:
364, Issue:
1844
Journal Article
PDF
