Greenland's ice sheet melts as temperatures rise*

    * Story Highlights
    * Greenland's ice melt area increased 30% in 30 years, one scientist
says
    * The island is now losing more ice each year than it gains from new
snow
    * This melting ice is causing sea levels to rise around the world
    * Scientists fear low-lying areas could be flooded if seas continue
to rise

By Heather O'Neill

ILULISSAT, Greenland (CNN) -- From the air, Greenland's ice sheet, the
second largest on Earth, appears to be perfectly still.
Boat

A boat sails by an iceberg floating in the Jacobshavn Bay near the town
of Ilulissat, Greenland.

But below the surface, the ice sheet is in constant motion, as ice built
up in the interior pushes toward the coast in the form of massive
glaciers. During warmer months, ice from these glaciers melts into the
ocean.

It's an age-old process that scientists say has speeded up in recent
decades because of global warming.

The fear is that melting ice from Greenland and other Arctic areas could
cause sea levels to rise enough to flood low-lying cities, such as
Shanghai, China, and New York City, displacing millions of people in the
process.

A recent report from the U.N.'s Intergovernmental Panel on Climate
Change, made up of scientists from around the world, estimates the sea
level rise by 2100 could be as much as 1½ feet.

"That sea level rise is only based on melt from ice sheets, and does not
include a new fast flow of ice we have detected in Greenland that is
generating additional icebergs," said Dr. Konrad Steffen, a climate
scientist with the University of Colorado, Boulder. Video Watch how
greenhouse gases cause temperatures to rise »

Steffen estimates sea levels could rise three feet over the next
century, a stark prediction that could wreak havoc around the world if
it comes to pass. Greenland holds enough ice to cause sea levels to rise
23 feet if the entire ice sheet melted, a development few scientists
expect to happen anytime soon. But global sea levels have been rising at
the rate of three millimeters per year since 1993.

For each of the past 17 years, Steffen has spent one month at a remote
research site called Swiss Camp, located 300 miles north of the Arctic
Circle in Greenland. He monitors the changing ice sheet through a
network of global positioning systems and weather stations, which have
recorded a dramatic rise in temperatures since the mid-1990s.

"When we came here in 1990, the first two, three years were actually
colder than normal. Then in 1994, 1995, it started to warm steadily and
since then, we've had a temperature increase during the winter months of
4.5 degrees centigrade, 8.1 degrees Fahrenheit, which is very large, the
largest temperature increase on earth," he said.

The rising temperatures feed what scientists call a "positive feedback
loop." As the air warms, it melts ice on the sea and snow on land. This
exposes more water and land to the sun. Those surfaces in turn absorb
more of the sun's heat, leading to more snow melt and ice melt.

"When you look at our satellite analysis, we can see the melt area of
Greenland over 30 years has increased by 30 percent," Steffen said.

Despite all the changes in Greenland, this is not the first time
temperatures have risen on the world's largest island. During the 1920s
and 1930s, there was a significant warming trend that occurred without
the level of man-made greenhouse gases recorded in our atmosphere today.
The majority of scientists say greenhouse gases are the chief cause of
global warming.

The fact Greenland has warmed before leads some scientists to question
how worried we should be about the current warming trend. Dr. Patrick
Michaels, a climatologist, is part of a small group of climate change
skeptics. He said Greenland's warm past didn't cause the ice sheet to
disappear.

"Well, this happened for 50 years in the early 20th century, and it
happened for a millennium after the end of the last ice age," he said.
"And the ice didn't shed off it."

But Dr. Jay Zwally, a climate scientist with NASA, said he thinks the
latest trend is different.

"The current warming trend in Greenland is very extensive and is not
likely to be explained by natural variability alone," he said. Zwally
said the warming is consistent with scientific predictions about the
effects of man-made greenhouse gases.

Last year, satellite data collected by NASA scientists revealed
Greenland is losing 100 billion tons of ice each year, more than it is
gaining from snowfall in the interior. Steffen and others have also
detected a new, faster movement of the ice sheet, causing the glaciers
to dump more ice into the ocean, where it melts and contributes to
sea-level rise.

Part of this faster flow is caused by moulins, deep holes in the ice
sheet that allow water to flow beneath the surface.

"During the summer months, as the ice sheet melts, large running rivers
of melt water snake down through the ice, to the bedrock base below,"
Steffen said.

Last year, researchers lowered a camera into a moulin to explore the
depth and flow of the melt water. Once the melt water from the surface
reaches the bedrock below the ice, it can lift the ice sheet and provide
a layer of viscosity for the ice to move faster toward the sea, a
process that could accelerate as Greenland continues to warm.

Steffen hopes his prediction of a three-foot rise in global sea level by
2100 won't become a reality. But he warned that even if we are able to
reduce the world's carbon output from cars and power plants, it will
take a long time for Earth's climate to stop warming and seas to stop
rising.

"Even if we reduce our carbon dioxide output, the climate will continue
to warm," he said. "So even by stopping the increase of carbon dioxide
today, we will have a warming, we will have sea level increase."