Sea Level
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Thanks to the satellite images of National Aeronautics and Space Administration (better known by the acronym NASA), together with the analysis of data and numbers provided by the Intergovernmental Panel on Climate Change (IPCC), it is now possible to monitor sea level change worldwide. NASA’s Sea Level Change Team, in fact, has succeeded in creating an interesting interactive map, freely available to everyone and easy to use, which serves to monitor not only the current sea and ocean level situation around the world but also to predict potential future scenarios.
It starts with data collected from satellites and ground-based instruments and then proceeds to computer simulations and analyses to arrive at projections of sea and ocean levels. These projections not only provide “snapshots” of the situation but also help the user understand the processes involved in sea-level rise over time. These processes obviously include the melting of glaciers and ice caps, but also the measurement of ocean waters that are capable of shifting their own circulation patterns as they warm and expand.
We offer the interactive map of the rising seas, but it is only fair to remind users, here below, how to use and interpret it. In the tool-guide that accompanies the map images, simply enter the desired decade (between 2020 and 2150); at this point, to view both the images and the numbers in detail, simply click on any point on the ocean or coastline on the map. The objective of the sea level projection tool is simple and clear: in a “warmer” climate (because it is warmed by rising temperatures), sea levels around the world have risen and, unfortunately, are expected to continue rising in the future. Projections of future sea level rise are crucial for both policy makers and coastal planners (architects and engineers) who seek to understand and take into account the impacts of sea level rise on communities themselves. This tool is therefore capable of predicting future scenarios and helps not only residents and citizens but also governments around the world.
NOTE: NASA’s sea level projection tool allows users to view and download sea level projection data contained specifically in the IPCC’s Sixth Assessment Report (AR6).
30 years of tracking sea-level rise
Exactly 30 years ago, scientists launched a satellite into orbit with the express purpose of monitoring and studying the rise and fall of the seas. This monitoring operation was previously carried out by man, who took the necessary measurements directly on the coast. On 10 August 1992, TOPEX-POSEIDON (this is the name of the satellite) was launched into space, capable of measuring, recording, storing and comparing data on the surface height of the oceans and seas worldwide. The results of the satellite measurements confirmed the observations that scientists had already made with their previous instruments directly on the coasts, i.e.: the seas are rising, and at an accelerating rate.
Satellite measurements have allowed scientists to discover and accurately note that the global mean sea level has risen by 10.1 centimetres (about 4 inches) since 1993. Over a period of 140 years, first with tide gauges, then also with satellites, it has been shown that the global sea level has risen by about 21-24 centimetres (i.e. 8-9 inches); it is as if the coasts of the (contiguous) United States were covered by 5 metres of water.
Credits: NASA’s Earth Observatory – More info at: Key Indicators: Global Mean Sea Level
Click on the corresponding button to view the graph and obtain more detailed information.
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Global mean sea level
103.8mm since 1993 -
Ocean Mass
2± 0.3 mm/yr
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Steric Height
1.3± 0.2 mm/yr
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Greenland ice mass change
269± 21 Gt/yr -
Antarctica ice mass change
142± 39 Gt/yr
Global Mean Sea Level
Global mean sea level: what is it?
It is the average height of the entire ocean surface. Its rise is mainly caused by two factors related to global warming: (i) the expansion of sea water due to warming and (ii) the addition of water from melting ice caps and land glaciers.
What are we observing?
The graph shows the global sea level change since 1993, an observation made by satellite altimeters. The black line plots the measurements, while the blue line shows the uncertainty associated with these measurements. Those shown are the latest available data (considering a delay of 4 months for the time used for processing).
Note: it should be noted that the data shown in the graph does not include the GIA (Glacial Isostatic Adjustment). To download the data with the GIA applied, simply click on the link below the graph.
Why does the figure matter?
The figure for global mean sea level is important because it is a true climate indicator that provides information on the melting of land ice and the warming of the oceans. For decades now, the global sea level has been rising, confirming that the climate is warming. The rate at which sea level rise, the so-called “annual rate of rise”, has increased from 0.08 inches/year (0.20 centimetres/year) in 1993 to the current annual rate of 0.17 inches/year (0.44 centimetres/year). These data are crucial to enable planners (scientists, engineers and even architects) to understand the “trajectory” of future sea-level rise. Further information on 30-year satellite recordings and data on the trajectory of global mean sea level rise is available by clicking the link provided here.
Reference: Willis, Hamlington, Fournier, 2023; Beckley et al., 2017; GMSL dataset.
Ocean Mass
What is meant by “ocean mass”?
It is nothing more than the “weight” of the ocean, determined by its gravitational pull.
What are we observing?
The graph shows satellite measurements of ocean mass since 2002; it is from the melting of the earth’s ice and the addition of ocean water that the rise in level we have been observing for years is derived. The graph shows a black line plotting the measurements taken while the blue shows the uncertainty, either increasing or decreasing, of these same measurements.
The now-retired GRACE (Gravity Recovery and Climate Experiment) satellite was the first to make these particular measurements and now the same measurements are made by GRACE Follow-On launched in 2018. These satellites observe the roughness and depressions of the Earth’s gravitational field as they pass over land, water and ice.
Why does the figure matter?
The increased risk of flooding and, consequently, the submergence of neighbouring coastlines, depends on the increase in ocean mass that causes the sea level to rise along the coasts. It follows that knowing the data is not only of interest but of extreme importance to avoid disasters that would be “irreparable”.
Reference: Watkins et al., 2015, doi: 10.1002/2014JB011547; GRACE and GRACE Follow-On JPL RL06Mv2 data.
Steric Height
Steric height: what is it?
The height of the sea surface increases not only when water is added, but also when the water heats up and its volume expands. Obviously, variations in salt content, or salinity, affect the sea level itself; these variations are known by the technical term “halo-steric heights” and “thermo-steric heights”.
What are we observing?
The measurement of ocean temperature and salinity from the surface to a depth of about 2,000 metres is carried out by a global system of floating ocean sensors (a system known as the “Argo”). The Argo floats are able to tell us how much of the known rise in sea level can be attributed to the rise in temperature due to the expansion of seawater.
Why does the figure matter?
Knowing that the ocean absorbs 90 per cent of the heat trapped in the Earth’s atmosphere and thanks to satellite measurements, we can now say that the warming and expansion of ocean water contributes to about a third of the sea level rise. We can also accurately identify and measure the contribution of processes to global average sea level rise through measurements of melting land ice that is added to ocean water.
Data files: https://www.ncei.noaa.gov/access/global-ocean-heat-content/fsl_global.html
Greenland
What are we observing?
The amount of ice that Greenland has lost since May 2002 is represented by the “notched” line on the graph, broken down and expressed in gigatonnes (billions of metric tonnes) of ice mass (i.e. the “weight” of the ice). Instead, the blue line (visible when clicking and dragging to zoom in) shows the uncertainty, low or high, associated with these measurements.
Data and measurements come from both the GRACE (Gravity Recovery and Climate Experiment, now decommissioned) satellites and the new GRACE Follow-On satellite (the follow-up mission to GRACE launched in 2018).
Why does the figure matter?
Greenland’s ice is melting rapidly and the melting is accelerating. The ocean is rising by about 1 millimetre for every 360 gigatonnes of ice lost. It is noted that the sea level has risen since 2002 by about 2.5 inches, or about 63 millimetres. At this rate, it is inevitable that sea level rise will increase coastal flooding and eventually submerge some coastal communities.
Reference: Watkins et al., 2015, doi: 10.1002/2014JB011547; GRACE and GRACE Follow-On JPL RL06Mv2 data
Antarctica
What are we observing?
As can be seen from the map, the jagged line depicted on the map shows the losses of ice sheets and glaciers on the Antarctic continent since May 2002 (values expressed in giga tonnes, or billions of metric tonnes) of ice mass – the “weight” of ice. The blue line (which appears when you click and drag the mouse pointer to zoom in) shows the uncertainty, low or high, associated with these measurements. The uncertainty (or the give and take number), describes the range from the mean, or average, within which there is a high probability that the true number resides.
Data and measurements come from both the GRACE (Gravity Recovery and Climate Experiment, now decommissioned) satellites and the new GRACE Follow-On satellite (the follow-up mission to GRACE launched in 2018).
Why does the figure matter?
Although not so fast, Antarctica is losing ice as is Greenland. For every 360 gigatonnes of land ice lost, the ocean rises by about 1 millimetre and, taking the measurement from May 2002, the sea level has risen by about 2.5 inches, or 63 millimetres. At this rate, some coastal communities will soon be submerged as the same rise in sea level increases the number of coastal floods that contribute to submerging neighbouring lands.
Reference: Watkins et al., 2015, doi: 10.1002/2014JB011547; GRACE and GRACE Follow-On JPL RL06Mv2 data