Greenland is about four times the size of France and covered with a layer of ice almost 2 miles thick. Antarctica, with roughly the same depth of ice, is 10 times bigger.

When you’re talking about ice on Earth, those two are just about all that’s in the freezer.

The coastal ice in some areas of Greenland is thinning at a rate of 3 feet a year.

But coastal melting isn’t the only problem. Another concern is that the ice of Greenland isn’t frozen solid to the bedrock it rests on. There may be more water than anyone thought between the Greenland ice cube and bedrock.

What would that mean? Think about a skater. A skater isn’t really skating on ice but on water. The skater’s weight, concentrated on two narrow blades, melts the ice and makes a film of water that permits fast gliding.

So if there’s a lot of water under the ice of Greenland, the ice might slide faster toward the oceans. Sea levels could rise more quickly.

If all of Greenland’s ice melted, global sea levels would rise about 20 feet. The United States might be able to cope with such a rise, but for poor countries like India and Bangladesh, it would be catastrophic. So says Prasad Gogineni, a professor of computer and electrical engineering at Kansas University.

Gogineni and some colleagues in his department, as well as Dave Braaten, associate professor of physics and astronomy, are studying the problem.

In a previous project, Gogineni showed that the Greenland ice was moving faster toward the sea than had been thought. It was acting more like a melting ice cube sliding across a table top than one frozen to the table top.

The group has received about $7.5 million from the National Science Foundation and NASA to work on developing and testing radar that will detect how much water is under the Greenland ice.

Next summer, two vehicles, one a robot and one operated by a human crew, and both equipped with the radar being developed, will scoot around Greenland in target areas where something’s already known about the existence of water between ice and bedrock.

The purpose of the excursion, Braaten says, is to validate the new radar’s accuracy.

The researchers hope that the radar will tell not only whether a spot is frozen or melted but, if it is melted, also the depth of the fluid between ice and bedrock.

Why would there be any water under 2 miles of ice? For one, because of pressure melting caused by the sheer weight of the ice mass. Or there could be geothermal hot spots that melt the ice.

Might the ice be melting because we’re in one of those natural warm spells the Earth goes through? One such spell started 1,200 years ago. It lasted 400 years and, by the end, grapes were growing in Greenland.

“What’s new since then,” Braaten says, “is that we’re dumping HUGE amounts of greenhouse gases into the environment.”

Carbon dioxide concentrations in the atmosphere peaked historically at around 280 parts per million, Braaten says. Today’s figure is 21 percent higher than that.

The government of a Pacific island called Tuvalu made a plea last summer for countries to take in Tuvalu evacuees. Rising sea levels are already threatening the island.

If ice cubes as big as continents skate into the ocean, a whole lot of other people may be looking for higher ground, too.

Roger Martin is a research writer and editor for the Kansas University Center for Research and editor of Explore, KU’s research magazine Web site, which can be found at www.research.ku.edu. Martin’s e-mail address is rmartin@kucr.ku.edu.