Greenland on the Rise

Greenland's ice sheet is melting so fast that surprised scientists say they can almost watch the ground rise as it is relieved of the overlying weight.

The melting and the resulting rise in sea level is one of the hallmarks of global warming, but researchers are having to resort to some novel methods to overcome different seasonal and regional signals that obstruct their ability to measure the effect of rising temperatures.

(It's melting around the edges, for instance, where its coastal glaciers are calving icebergs out to sea, but the interior "mass balance" of the ice at high elevations is thought to be stable.)

This NASA satellite image shows the Jacobshavn Glacier, a major ice flow from western Greenland.  The arrow points to a gray area of rapidly thinning ice between the stable higher-elevation ice and the flowing glacier.

Rather than focusing on the ice itself, researchers at the University of Miami are using high-precision satellite-borne Global Positioning System instruments to measure changes in the height of the underlying land mass. Relieved of the weight of the ice, the land rebounds.

But measuring the problem is not so straightforward, because this process of rising land height has been going on for eons around the Northern Hemisphere. Most of Canada and much of the northern United States still is rebounding from the ice load of the last ice age, for example.

A new study published online in the journal Nature Geoscience gets around this problem in an interesting way. Instead of measuring the rise of Greenland's land, they are measuring the rate of change.

"We focus on vertical accelerations rather than velocities to avoid the confounding effects of past events," writes Yan Jiang and colleagues. "Our data show an acceleration of uplift over the past decade that represents an essentially instantaneous, elastic response to the recent accelerated melting of ice throughout the North Atlantic region."

The Miami researchers were surprised by their findings.  The land of some coastal areas is rising by nearly one inch per year, and the rate of acceleration suggests it will go up to as much as two inches per year by 2025.

"What's surprising, and a bit worrisome, is that the ice is melting so fast that we can actually see the land uplift in response," geophysicist Tim Dixon, a co-author, said in a statement.  "Even more surprising, the rise seems to be accelerating, implying that melting is accelerating."