Greenland and Antarctica have lost four trillion tonnes of ice in 20 years.
A new, definitive study of satellite data has found that polar ice sheets are now melting three times faster than they did in the 1990s.
The amount of ice lost from Greenland and Antarctica is enough to raise world sea levels by almost one millimetre a year. Since 1992, it has added more than 1cm to global sea levels – contributing around a fifth of the total rise. About two thirds of the ice loss was from Greenland and the remainder from Antarctica, said scientists.
The new survey is said to be the most accurate assessment to date, ending 20 years of uncertainty. It confirms that, with the exception of East Antarctica, both land masses are losing ice. But big differences in the pace of change were seen at each pole.
The new research concludes that Antarctica is melting, but points to the smaller ice sheet in Greenland, which covers most of the island, as the bigger and more pressing issue. Its melt rate has grown from about 55 billion tons a year in the 1990s to almost 290 billion tons a year recently, according to the study.
The vast polar ice sheets lock up unimaginable amounts of water. The Antarctic ice sheet contains 30 million cubic kilometres of ice and holds around 90% of all the fresh water on the surface of the Earth.
If the whole Antarctic ice sheet melted, sea levels would rise by more than 60 metres. The Greenland ice sheet is much smaller, but would add seven metres to sea levels if it all melted away.