Melting ice causing tiny sea level rise

Together, the lost ice is raising sea levels annually by a tiny fraction – about a hair's breadth spread evenly around the world's oceans.

This is despite the fact that, in keeping with Archimedes' principal, floating ice displaces its own volume of fluid and should not add more water when it melts.

The rise is due to differences in the density and temperature of ice and salty sea water.

The iceberg struck by the Titanic on her maiden voyage in April 1912 was between 200ft and 400ft long, 50 to 100ft high and weighed at least 136,000 tonnes, experts estimate.

According to the new research, based on satellite data and computer simulations, around 1.5 million times this amount of floating ice is disappearing each year.

Spread across the global oceans, the melting ice increases sea level by 49 micrometres a year, about the width of a human hair.

The findings, published yesterday in the journal Geophysical Research Letters, provide the first assessment of how quickly floating sea ice is being lost today.

Lead researcher Professor Andrew Shepherd, from the University of Leeds, said: "Over recent decades there have been dramatic reductions in the quantity of Earth's floating ice, including collapses of Antarctic ice shelves and the retreat of Arctic sea ice. These changes have had major impacts on regional climate."

The melting of floating ice should be considered in assessments of sea levels, he said.

The greatest losses of floating ice were due to the rapid retreat of Arctic sea ice, and the collapse and thinning of ice shelves in the Antarctic Peninsula and the Amundsen Sea, part of the Southern Ocean.

Sea ice is formed on the surface of sea water when the ocean freezes; ice shelves are floating platforms of ice at the mouth of glaciers or ice-sheet fringes.