Ice height changes and sea level rise

 

Changes in ice height and sea level change

 

Measuring ice mass and relating to sea level rise

 Measuring the mass change of ice height and using other data like ice thickness and its volume to calculate its mass. Over time the changes are obtained from ever-increasing precision measurements from satellites.

 Over the recent period, warmer conditions have led to loss of ice mass over Antarctica, Greenland and Arctic regions. Every 360 gigatons of added melt water raises global sea level by one millimetre. This phenomenon has been responsible for a third of the rise.

 How are the ice height changes measured?

 Scientists radar and laser altimeters use radio and light pulses respectively and the precise height of the satellite taking the measurements to calculate ice height. Over time such data provide changes.

 Radar altimeters can measure over a swathe of 1700m and can see through clouds. The of a laser is smaller at about 14m diameter. The laser pulses cannot penetrate thick clouds. Radar measurements are less precise. Laser measurements are useful with steep changes.

The first satellite to measure ice elevation using radar was NASA’s Seasat in 1978. Now several satellites use radar altimeters and provide continuous ice elevation data for Greenland and Antarctica since 1991.

 In 2003 NASA launched its first dedicated satellite Ice, Cloud and land Elevation Satellite (ICESat). In 2018 it launched ICESat2 which enables estimation of the annual height change of the Greenland and Antarctic Ice Sheets to within 4mm. Other countries have also ice height measuring instruments in space.

 Observations so far

Changes in land ice thickness in Antarctica between 2003-2009 and 2018-2019. Losses around the edges of Greenland and West Antarctica have contributed 14mm to sea level rise since 2003, which is a third of observed sea level rise.

 Over the last 16 years Greenland has lost more ice than Antarctica. The Greenland ice loss is estimated at 200 gigatons per year. Warmer summers and warmer ocean water are thought to be responsible. Antarctica’s ice sheet which is about 8 times larger than Greenland has been losing about 118 gigatons per year due to warmer oceans. However, these losses are partly offset by snow and ice accretion in parts of Eastern regions.

Future studies

Scientists are working to build better ice mass balance models by combining observations from various satellites. Such models will enable future changes in ice sheets and their implications for climate change and in particular sea level rise.

 (Extracts from Kasha Patel, NASA)