Week 1: Oceans and Climate > Topic 1g - Measuring sea ice retreat

Along with a gradual warming of the oceans, melting of the Greenland and Antarctic ice sheets are main contributors to the sea level rise of our oceans. Satellite altimetry can help to quantify these two contributions and improve predictions of future changes in sea level.

Sea ice

For three decades satellites have been documenting the decline of Arctic summer sea ice. This shows that the ice-covered area during the summer minimum (September) has been shrinking much faster than expected from climate models.

The loss of Arctic summer ice is important for several reasons:

SAR altimeters from CryoSat and Sentinel-3 satellites can measure sea ice thickness, although only during the winter months. Melt-water on the ice surface prevents reliable measurements during the polar summer.

Land ice

While melting sea ice does not contribute to sea level rise, melting land ice in Greenland and Antarctica has a direct effect on sea level by adding water to the oceans. Recent satellite observations from Greenland and Antarctica indicate that this rate of ice loss in these areas may be increasing.

Altimeters can measure changes to the topography of ice sheets. The spatial resolution of early altimeters prevented accurate measurements from being made over the ice sheet margins, where most of the changes take place. Modern SAR altimetry (CryoSat and Sentinel-3) can measure changes also over the ice sheet margins. This has led to more accurate estimates of ice loss and the contribution this makes to global sea level rise.

Changes to the volume of ice sheets can also be calculated from satellite gravimetry (GRACE and GOCE).

Optional mini task:

Visit the US National Snow and Ice Data Centre’s interactive sea ice graph You can use the legend on the side to view the current sea ice extent for the Arctic or Antarctic, as well as each year from 1979. How does this year compare to other years?

Featured Educators:

Optional further reading

Explore the data

EUMETSAT Oceans MOOC Data Viewer

View featured satellites on the satellite tracking app

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View featured imagery, animations and related links below


Polar sea ice concentration of the northern and southern hemispheres throughout 2016, as seen by the DMSP and EUMETSAT’s Metop satellites.

Between 2011 and 2014, Greenland lost around one trillion tonnes of ice. This corresponds to a 0.75 mm contribution to global sea-level rise each year – about twice the average of the preceding two decades. These results from the UK Centre for Polar Observation and Modelling (CPOM) at the University of Leeds combine data from the CryoSat mission with a regional climate model to map changes in Greenland ice-sheet mass.

Sea ice age in March 1988, 2011, 2012 and 2013, determined using satellite observations and drifting buoy records to track the movement of ice floes

NOAA Geophysical Fluid Dynamics Laboratory climate model simulation shows a dramatic decrease in late summer Arctic sea ice concentrations by 2085

Ice freeboard (in meters) estimates from Cryosat-2 in March 2011, 2012 and 2013. Freeboard is used as a proxy for ice thickness.

Artist’s impression of the CryoSat satellite in orbit.

The launch of the CryoSat spacecraft was unfortunately aborted on 8 October 2005 due to a malfunction of its Rockot launcher, which resulted in the total loss of the spacecraft.

Artist’s impression of CryoSat in orbit

Arctic sea ice concentration on 25 December 2015

Arctic sea ice concentration on 25 June 2014

Autumn Arctic sea-ice thickness as measured by CryoSat between 2010 and 2014.