Greenland and Antarctic melting has surpassed mountain glacier and ice cap melting when it comes to sea level rise, with rates exceeding modeling forecasts, a new report finds.

Melting ice sheets in Greenland and the Antarctic are becoming the biggest contributors to the rise in the global sea level, overtaking ice loss from Earth’s mountain glaciers and ice caps, according to a study published in the American Geophysical Union’s peer-reviewed journal Geophysical Research Letters.

Greenland and Antarctic melting is becoming the dominate contributor to sea level rise at a rate faster than forecast models have predicted, the study says. By 2006, Greenland and Antarctica ice sheets were losing a combined 475 gigatonnes each year on average. That’s enough to raise the global sea level .05 inches per year.

The research team, led by Eric Rignot of NASA’s Jet Propulsion Laboratory in Pasadena and the University of California, Irvine, found that for each year over the 18-year study, the Greenland ice sheet lost mass faster than it had the year before — by an average of 21.9 gigatonnes per year. In Antarctica, the annual increase in ice mass lost averaged 14.5 gigatonnes.