Rapidly melting Greenland may be shedding its ice even faster than anyone suspected, new research suggests.

A study just out in the journal Science Advances finds that previous studies may have underestimated the current rate of mass loss on the Greenland ice sheet by about 18 billion tonnes per year.
Generally, scientists estimate ice loss in Greenland (and elsewhere around the world) using data from satellites. But the new study suggests these satellite studies may have included some incorrect assumptions, causing them to miscalculate the amount of mass actually disappearing from the ice sheet each year.

The assertion revolves around a concept known as "glacial isostatic adjustment", or the tendency of land to bounce back after a large weight of ice has been removed from it. Over the past 25,000 years, since the last great Ice Age, the planet's surface has been slowly springing back into place.

An important part of this effect is driven by the flowing of the Earth's mantle, a layer of thick, oozing rock beneath the Earth's crust, said Michael Bevis, a geophysicist at the Ohio State University and a co-author on the new study. When a heavy weight, such as a huge ice sheet, forms on the Earth's surface, the resulting high pressure causes the rocky mantle to begin flowing out from underneath it. When the weight is removed, the mantle gradually begins to flow back into place.