LONDON (Reuters) - Antarctica is melting, adding to the inexorable rise in global sea levels, endangering millions of lives and whole economies, leading scientists said on Monday.

But while the effect is well known after years of monitoring from land and space, the reasons for the sea warming are not.

"We know sea levels will rise. We need to know by how much and why," Anthony Payne of the University of Bristol and one of the organizers of a major scientific conference in London, told Reuters on the sidelines of the meeting at the Royal Society, Britain’s national academy of science.

"This has implications for the whole world -- most people and industries are in coastal areas," he added.