The Guardian article goes on to say:
“Our results and those of everyone else show we are losing a huge amount of water into the oceans every year,” said Prof John Wahr of the University of Colorado. “People should be just as worried about the melting of the world’s ice as they were before.”
His team’s study, published in the journal Nature, concludes that between 443-629bn tonnes of meltwater overall are added to the world’s oceans each year. This is raising sea level by about 1.5mm a year, the team reports, in addition to the 2mm a year caused by expansion of the warming ocean.
This same cherry-picked factoid has been doing the rounds of the "skeptic" blogs since the article's publication, and has made it's way here.
For reference, the paper this is all based on (subscription required): http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10847.html