(CNN) Greenland's massive ice sheets contain enough water to raise global sea levels by 23 feet, and a new study shows that they are melting at a rate "unprecedented" over centuries -- and likely thousands of years.

The study, published Thursday in the scientific journal Nature , found that Greenland's ice loss accelerated rapidly in the past two decades after remaining relatively stable since the dawn of the Industrial Revolution in the mid-1800s.

Today, Greenland's ice sheets are melting at a rate 50% higher than pre-industrial levels and 33% above 20th-century levels, the scientists found.

"What we were able to show is that the melting that Greenland is experiencing today is really unprecedented and off the charts in the longer-term context," said Sarah Das, an associate scientist at the Woods Hole Oceanographic Institution and a co-author of the study.