LONDON, Dec 5 : The melting of the Antarctic and Greenland ice sheets has raised sea levels by 11.1 millimeters since 1992, a fifth of the total rise which threatens low-lying regions around the globe, a new study published tomorrow said. The results of the study involving 47 researchers from 26 laboratories which was supported by the European Space Agency and the National Aeronautics and Space Administration give the most accurate measurements of ice loss to date, they said in the journal Science. (agencies)