This artist's impression shows the EU's CryoSat 2 satellite as it would appear in orbit over an ice sheet. Its mission is to precisely monitor changes in the thickness of the vast ice sheets that overlay Greenland and Antarctica and of the marine ice floating in the polar oceans. (ESA - AOES Medialab)

The European Space Agency is launching a satellite that scientists hope will help them pin down the effects of global warming on the Earth's ice packs.

The CryoSat 2 mission, which starts Thursday after years of delays, will be able to track detailed changes in polar ice.

Although most scientists agree that global warming is significantly affecting the Earth's ice sheets, many also say too little is known with certainty.

"We hope to find out more about the role the sea ice plays for the climate system and more about the height of the land ice," said Heinrich Miller, one of the two CryoSat project directors.

"We know that it is dwindling but we don't know exactly what mechanisms are at work," Miller said. CryoSat 2 will be the only satellite that can deliver the necessary data, he said.

Earlier satellites helped lay the groundwork for decades worth of research on the Arctic and Antarctic ice sheets, but have gone out of operation without being replaced, Miller said.

The CryoSat mission was to start in 2005 but suffered a severe setback when the launcher rocket failed and the satellite was lost, costing about $147 million.

In 2006, the agency, known as ESA, decided to rebuild the satellite and launch it in 2009. Lift-off from the Baikonur Cosmodrome in Kazakhstan was postponed several times, most recently in February due to technical problems with the transport rocket.

ESA says its new 700-kilogram satellite is the "most sophisticated ever to investigate the Earth's ice fields." It aims to operate for at least three to five years, hopefully longer, Miller said, and the agency estimates the total cost for the mission at $187 million.

Satellite can pinpoint changes of one centimetre

From 720 kilometres above Earth's surface, CryoSat will use radar technology to measure the thickness of both land and floating ice and pinpoint changes to within one centimetre. The Antarctic ice sheet can be up to five kilometres thick.

Recent summers have seen record lows in the extent of summer ice cover in the Arctic sea, ESA said, but for coastal cities and islands, detailed information about ice thickness may be a question of survival.

If all of the Earth's polar ice and glaciers were to melt, sea levels could rise up to 70 metres, Miller said. If only Greenland became ice-free, it would mean a 6.5-metre rise, he added.

Pessimists expect a sea rise of two to three metres by the year 2100, he said.

In its 2007 report, the Intergovernmental Panel on Climate Change projects only some 20 to 60 centimetres, without calculating the possibility of a dramatic increase in the rate of polar ice melt.

"It is just very hard to predict this," Miller said, because there are multiple reasons for the loss of ice mass — not only warming, but also changes in sea currents. "By repeated observation, we hope to register even small changes within a brief period of time."