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:

  • Open water absorbs far more of the incoming solar energy than an ice covered ocean, so the loss of ice contributes to increase global warming

  • The ice is a critical part of polar ecosystems, so the loss of ice will have profound impacts on Arctic life and humans who depend on Arctic living resources for their livelihoods

  • An opening up of the Arctic will increase ship traffic and exploration for oil and other resources in the Arctic, with its own potential problems

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:

  • Dr Val Byfield

Explore the data

EUMETSAT Oceans MOOC Data Viewer

View featured satellites on the satellite tracking app

Don’t forget you can download the video and transcript with the links on the right.


Arctic Sea Ice thickness (10 Year average)

Arctic sea ice thickness in the 1950s and as predicted for 2050s.

Animation - Greenland Ice Loss

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.

Arctic Sea Ice over 20 years

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

Climate model - Summer Arctic sea ice

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

Arctic Ice freeboard (thickness)

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.

Arctic 2010 Sea Ice Maximum


Artist’s impression of CryoSat in orbit

Arctic Sea Ice December 2015

Arctic sea ice concentration on 25 December 2015

Arctic Sea Ice June 2014

Arctic sea ice concentration on 25 June 2014

Changes in Autumn sea ice

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