Scientists warn that glaciers across the world's third largest continental ice field could disappear within the next 60 years.

SHOWS: (W5) SANTA CRUZ, ARGENTINA - Argentine scientists warned on Tuesday (March 11) that a giant glacier in Patagonia could disappear before the end of the century.

Experts from the Argentine government science agency CONICET reported that the Viedma Glacier, located in Argentina's southern Santa Cruz province, has retreated one kilometre in length since 1930.

Comparative photos showed where ice that used to spread across a valley below has already disappeared.

Greenpeace has mounted a campaign against global warming centred on the find, which follows on from similar reports of mass losses in the nearby Upsala Glacier.

Both the Viedma and the Upsala glaciers are part of the huge South Patagonian Ice Field, the third largest expanse of continental ice after Greenland and Antarctica.

Scientists warn that the melt is going on not only in these large fronts, but across the field.

"You can see a very marked reduction in the glaciers [of this region], and over the last 20 years -- so from 1984 to 2004, for which we have conducted our study -- the glaciers have retreated between 10 to 20 percent, the rate differing in each region. With that velocity, that could mean that if the tendencies continue it is very possible that the bodies of ice that we can see at the moment could disappear completely in approximately 50, 60 or 70 years," said CONICET geoscientist Ricardo Villalba.

Scientists describe glaciers as the world's thermometers because they are very sensitive to changes in the climate.

The South Patagonian Ice Field has 45 main glaciers, and various studies show that the majority of them are retreating.

Scientists also argue that the few that aren't following the trend are being protected by special, temporary conditions that will eventually be overcome.

Glacial melting, along with the expansion of water in warmer temperatures, could provoke rising sea levels.

The U.N. Climate Panel estimates that seas will rise by 18-59 cms by 2100 because of global warming stoked by human use of fossil fuels.

Antarctica and Greenland now holds enough ice to raise world sea levels by almost 67 metres if it all melted. The impact the South Patagonian Ice Field could make is still uncertain, because scientists are yet to measure the exact ice mass of the field.