Glossary
This page is an illustrated glossary to understand the main key drivers of global and local sea level change.
All definitions are from the IPCC, 2021 : Climate Change 2021 : The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change[Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, In press, doi:10.1017/9781009157896.
Global sea level changes
“Sea level change arises from processes acting on a range of spatial and temporal scales, in the ocean, cryosphere, solid Earth, atmosphere and on land” (Box 9.1 IPCC 2021). Below are the main contributors. The page starts with the interactive illustration below (sea-level rise contributors), by clicking on the different contributors, other illustrations are displayed.
Sea level science episode 1 - how can we predict sea level rise in the future?
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The Antarctic ice sheet
The Antarctic ice sheet is “an ice body [covering the continent of Antarctica] [...] that has formed over thousands of years through accumulation and compaction of snow. It [...] flows outward from a high central ice plateau with a small average surface slope. The margins usually slope more steeply, and most ice is discharged through fast-flowing ice streams or outlet glaciers, often into the sea or into ice shelves floating on the sea.” (IPCC, 2021)
The Greenland and Antarctic ice sheets are the largest reservoirs of frozen freshwater and therefore potentially the largest contributors to sea level rise. Fluctuations in ice-sheet volume arise from the imbalance between accumulation (either at the ice-sheet surface or on the underside of ice shelves) and loss from sublimation, surface and basal melting, and iceberg calving.” (IPCC, 2021)
Antarctica, a game changer for sea level rise
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The Greenland ice sheet
The Greenland ice sheet is “an ice body [...] that has formed over thousands of years through accumulation and compaction of snow. It [...] flows outward from a high central ice plateau with a small average surface slope. The margins usually slope more steeply, and most ice is discharged through fast-flowing ice streams or outlet glaciers, often into the sea or into ice shelves floating on the sea.” (IPCC, 2021)
“The Greenland and Antarctic ice sheets are the largest reservoirs of frozen freshwater and therefore potentially the largest contributors to sea level rise. Fluctuations in ice-sheet volume arise from the imbalance between accumulation (either at the ice-sheet surface or on the underside of ice shelves) and loss from sublimation, surface and basal melting, and iceberg calving.” (IPCC, 2021)
Exploring the Vulnerability of the Greenland Ice Sheet
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Ice loss from the Greenland ice sheet involves primarily surface and frontal melting as well as iceberg calving.
Mountain glaciers
“Glaciers contribute to sea level change via an imbalance between mass gain and mass loss processes, which leads to adjustments in the glacier geometry over an extended period of time, called the response time. The response time may range from a few years to a few hundred years.” (IPCC, 2021)
Vanishing glaciers: a cause of sea-level rise and a threat to water supply
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Land-water storage
“Land-water storage includes surface water, soil moisture, groundwater storage and snow, but excludes water stored in glaciers and ice sheets. Changes in land-water storage can be caused either by direct human intervention in the water cycle (e.g., storage of water in reservoirs by building dams in rivers, groundwater extraction for consumption and irrigation, or deforestation) or by climate variations (e.g., changes in the amount of water in internally drained lakes and wetlands, the canopy, the soil, the permafrost and the snowpack).” (IPCC, 2021)
Land-water storage: water surface, snow, groundwater storage and soil moisture contribute to a small amount of sea-level change.
Thermal expansion
“Thermosteric sea level change (also referred to as ‘thermal expansion’) occurs as a result of changes in ocean temperature: increasing temperature reduces ocean density and increases the volume per unit of mass.” (IPCC, 2021)
Regional sea level
This webtool presents regional sea level changes due to non-uniform thermal expansion and other processes due to wind, as well as changes due to gravitational, rotational and deformational effects. However, there are additional effects causing sea level changes at different timescales such as local vertical land motions and storms causing extreme sea levels, as shown below.
Regional sea level change is ”relative to a datum at spatial scales smaller than 100 km.” (IPCC, 2021)
It can be influenced by : - Vertical Land Motion - Regionalisation of sea level rise - Extreme sea levels : tides, waves, storm, etc.