Ice sheets covering Greenland and Antarctica are melting three times faster today than in the 1990s, according to a "definitive" study of satellite data.
The amount of ice lost is enough to raise world sea levels by almost one millimetre a year.
Since 1992, it has added 11.1mm to global sea levels – contributing around one-fifth of the total rise.
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About two-thirds of the ice loss was from Greenland and the remainder from Antarctica, said scientists.
Until now, there has been confusion over what is happening to the ice sheets in a warming world.
Estimates have differed greatly, with some studies even suggesting gains rather than losses.
The new survey is said to be the most accurate assessment to date, ending 20 years of uncertainty.
Study leader Professor Andrew Shepherd, from Leeds University, said: "The success of this venture is due to the co-operation of the international scientific community, and the provision of precise satellite sensors by space agencies.
"Without these efforts, we would not be in a position to tell people with confidence how ice sheets have changed, and to end the uncertainty that has existed for many years."