Scientists have mapped the elevation changes of glaciers in Antarctica and Greenland and found an alarming fact: the Earth's ice sheets are rapidly declining.

Veit Heim, from the Alfred Wegener Institute in Bremerhaven, Germany, who led a study that examined the current surface elevation of Greenlandic and Antarctic ice sheet, said that the maps that they have developed using data from European Space Agency's CryoSat mission, reveal the present day state of icy surfaces and the images show that the elevation of ice sheets has significantly changed because of melting.

For the new study published in The Cryosphere journal, Heim and colleagues used data from the CryoSat-2 altimeter SIRAL, a radar altimeter that measures the elevation of ice sheets using laser or radar pulses and which gives scientists idea on the measurements of ice in the oceans and track the changes in the ice sheets and found that the volume loss for the ice sheets in Antarctica and Greenland is at 500 cubic kilometers a year.

"The combined volume change of Greenland and Antarctica for the observation period is estimated to be -503 ± 107 km3 yr-1." the researchers wrote [pdf]. "Greenland contributes nearly 75 % to the total volume change with -375 ± 24 km3 yr-1"

Greenland alone loses approximately 375 cubic kilometers annually and the biggest changes in elevation were detected in West Antarctica's Pine Island Glacier and West Greenland's Jakobshavn Glacier. Study author Angelika Humber, from the Alfred Wegener Institute, said that when they compared the new data with those from 5 years ago, they found that Greenland's volume loss has doubled.

The melting of ice sheets is often cited as one of the unwanted consequences of global warming as the warming climate causes the melting of large bodies of ice. CryoSat Mission Scientist Mark Drinkwater said that the findings of the study give an insight on the effects of climate change on the large ice sheets on Earth.

"This is particularly evident in parts of the Antarctic peninsula, where some of the more remarkable features add testimony on the impact of sustained peninsula warming at rates several times the global average," Drinkwater said.

The findings of the study gives an accurate measure of how much the ice sheets are declining and this is crucial not only for predicting the rise of sea levels but also in developing more precise climate models for the future.