Greenland ice loss. The loss of floating ice in 2008 from Greenland’s glaciers would cover an area twice the size of Manhattan Island in the US, according to the research team. Jason Box, an associate professor of geography at Ohio State, said that the loss of ice since the year 2000 is 355.4 square miles (920.5 square kilometers), or more than 10 times the size of Manhattan.

We now know that the climate doesn’t have to warm any more for Greenland to continue losing ice. It has probably passed the point where it could maintain the mass of ice that we remember.

But that doesn’t mean that Greenland’s ice will all disappear. It’s likely that it will probably adjust to a new ‘equilibrium’ but before it reaches the equilibrium, it will shed a lot more ice. Greenland is deglaciating and actually has been doing so for most of the past half-century.

The research team has been monitoring satellite images of Greenland to gauge just how much ice flows from landlocked glaciers towards the ocean to form floating ice shelves. Eventually, large pieces of these ice shelves will break off into the sea, speeding up the flow of more glacial ice to add to the shelves.

Warming of the climate around Greenland is believed to have added to the increased flow of ice outward from the mainland via these huge glaciers.

We know that snowfall rates have increased recently in this region, but that hasn’t been enough to compensate for the increased melt rate of the ice that we’re seeing now.

—Jason Box

Using daily images from instruments called MODIS (Moderate Resolution Imaging Spectroradiometer) aboard two of NASA’s satellites, Box and his team are able to monitor changes in 32 of the largest glaciers along Greenland’s coast.

They determined that during the summer of 2006-2007, the floating ice shelves at the seaward end of those glaciers had diminished by 24.29 square miles (62.9 square kilometers. But one year later—the summer of 2007-2008—the ice loss had nearly tripled to nearly 71 square miles (183.8 square kilometers). Much of this additional loss is from a single large floating ice tongue called the Petermann glacier.

Late this summer, a massive 11-square-mile (29-square kilometer) chunk broke off from the tongue of the Petermann Glacier in Northern Greenland. At the time, they also noted that a massive crack further up the ice shelf suggested an even larger piece of ice would soon crack off.

Their research is supported in part by the National Science Foundation and the National Aeronautics and Space Administration.

Antarctic bedrock. The results in the Antarctic study came from trio of global positioning system (GPS) sensor networks on the continent. Terry Wilson, associate professor of earth sciences at Ohio State University, leads POLENET, a growing network of GPS trackers and seismic sensors implanted in the bedrock beneath the West Antarctic Ice Sheet (WAIS). POLENET is reoccupying sites previously measured by the West Antarctic GPS Network (WAGN) and the Transantarctic Mountains Deformation (TAMDEF) network.

In separate sessions at the AGU meeting, Michael Bevis, Ohio Eminent Scholar in geodyamics and professor of earth sciences at Ohio State, presented results from WAGN, while doctoral student Michael Willis presented results from TAMDEF.

Taken together, the three projects yield the best view yet of what’s happening under the ice.

When satellites measure the height of the WAIS, scientists calculate ice thickness by subtracting the height of the earth beneath it. They must take into account whether the bedrock is rising or falling. Ice weighs down the bedrock, but as the ice melts, the earth slowly rebounds.

Gravity measurements, too, rely on knowledge of the bedrock. As the crust under Antarctica rises, the mantle layer below it flows in to fill the gap. That mass change must be subtracted from Gravity Recovery and Climate Experiment (GRACE) satellite measurements in order to isolate gravity changes caused by the thickening or thinning of the ice.

Before POLENET and its more spatially limited predecessors, scientists had few direct measurements of the bedrock. They had to rely on computer models, which now appear to be incorrect.

When you compare how fast the earth is rising, and where, to the models of where ice is being lost and how much is lost—they don’t match. There are places where the models predict no crustal uplift, where we see several millimeters of uplift per year. We even have evidence of other places sinking, which is not predicted by any of the models.

—Terry Wilson

POLENET’s GPS sensors measure how much the crust is rising or falling, while the seismic sensors measure the stiffness of the bedrock—a key factor for predicting how much the bedrock will rise in the future.

We’re pinning down both parts of this problem, which will improve the correction made to the satellite data, which will in turn improve what we know about whether we’re gaining ice or losing ice.

—Terry Wilson

Better estimates of sea level rise can then follow.

POLENET scientists have been implanting sensors in Antarctica since December 2007. The network will be complete in 2010 and will record data into 2012. Selected sites may remain as a permanent Antarctic observational network.

Ohio State’s POLENET partners in the United States are Pennsylvania State University, the University of Texas at Austin, New Mexico Tech, Washington University, the Jet Propulsion Laboratory, and the University of Memphis. A host of international partners are part of the effort as well. POLENET is funded by the National Science Foundation.