Will the Ice Cap Turn To Slush?

Just before takeoff, Lars Ahren glances back from the cockpit of his Twin Otter at the four passengers crammed into a cabin filled with boxes of fresh vegetables.

With a grin as wide as his bushy handlebar mustache, he quips, "Let us know if you get too warm back there. And if you get hungry, help yourself."

With our seat belts securely fastened and no tray table to return to the upright position, we're off to our destination - a Canadian icebreaker locked in the grip of a giant ice floe some 300 miles north of Prudhoe Bay, Alaska.

During the next 13 months, the ship will host teams of scientists seeking answers to a basic question about global warming: If the average temperature rises, how much of the 4.6 million square miles of Arctic ice would turn to slush?

Right now, scientists concede that the models they have created to estimate how much ice will melt during summer months are flawed.

But scientists aboard Des Groseilliers, the Canadian icebreaker trapped amid the arctic ice, hope to learn more about some of the uncertainties that lead to these flawed forecasts.

Their project, called the Surface Heat Budget of the Arctic Ocean (SHEBA), will measure the interactions between the polar sea, ice, atmosphere, and sun in unprecedented detail. It is the first Arctic expedition to try to gather the hard evidence on these relationships over a full year.

Funded through the National Science Foundation (NSF) and the Office of Naval Research, the SHEBA project is part of a larger effort to understand the potential effects of climate change on this sensitive region.

Problematic models

The current models predict that a doubling of carbon dioxide (CO2) in the atmosphere would trap more heat, meaning that the Arctic ice cap could melt in five decades, says Mike Ledbetter, director of the NSF's Arctic System Science Program.

If that were to happen, he explains, the spread of fresh water into the Atlantic, as well as the warming at the pole, would profoundly shift circulation in the oceans and atmosphere - altering weather patterns and fisheries worldwide, threatening the survival of cultures and ecosystems that ring the Arctic Ocean - not to mention what it would do to beachfront property in warmer climes, like Hilton Head, S.C.

But the current computer models tend to overestimate the amount of ice that actually melts.

Why? Because scientists have never been able get out into the field and closely measure the complex interrelation of solar radiation, ice, snow, open water, seawater beneath the ice, and clouds. As a result, when climate modelers try to tell their computers how to mimic conditions here, they have to employ a fair bit of guesswork.

"We just don't know the processes involved well enough," acknowledges John Kutzbach, a climate modeler at the University of Wisconsin at Madison.

Getting it right

To accurately forecast the effects of climate change on the Arctic, scientists must better understand two processes, says the project's chief scientist, Don Perovich, with the US Army Corps of Engineers' Cold Regions Research and Engineering Laboratory in Hanover, N.H.

One is ability of snow and ice to reflect large amounts of solar radiation back into space. When the ice pack thaws, this reflectivity, or albedo, begins to fall as snow melts, because ponds of melted water form, which are darker and therefore absorb more solar radiation. Also, when snow melts, it can expose the darker ice beneath it. As darker and darker ice is uncovered, the surface absorbs more solar radiation, and the heating accelerates.

This "positive feedback" is stronger at the poles than at lower latitudes, because the change in albedo is more drastic at the poles than at lower latitudes, where ice and snow cover are less extensive. Indeed, researchers have calculated that a 2-to 3-degree average rise in temperatures at lower latitudes could yield a 4-to 6-degree increase at the poles. But again, no one really knows if that range is too high or too low - no one has ever taken the Arctic measurements that would arrest wrong assumptions.

The second process involves the reflective properties of clouds. Clouds build as exposed seawater and melt water evaporate, and they can act as sunshades, reducing the amount of solar radiation that otherwise would heat the sea and melt the ice and snow. But clouds also can trap heat between them and the surface. No one is certain which effect from clouds would gain the upper hand.

SHEBA will not be alone studying the atmosphere of the Arctic this winter. A four-member team is also spending the winter on the summit of Greenland's ice cap to measure the atmosphere's chemistry and see how it gets bound up in the ice and snow. The data the team collects are expected to help climatologists do a better job of "reading" core samples from Greenland's ice, which are used to reconstruct past climate changes. Meanwhile, researchers are taking long-term measurements of the seasonal uptake and release of carbon dioxide in the Alaskan tundra, a significant "sink" for CO2.

An icy reception

Some two hours after leaving Deadhorse, Mr. Ahren begins his descent toward the SHEBA ice station. Within a few minutes, the plane drops below a thick layer of clouds, revealing broad white floes bounded by gray rivers of thinner ice and turquoise-tinted "leads," or edges. Off to the right side of the plane, the 322-foot Des Groseilliers appears - a tiny island of steel that serves as the project's hotel, supply depot, and communications center. After the plane lands and slows to a stop, we tug on mittens, zip up parkas, pull down goggles, and step out onto the frozen Arctic Ocean.

The icy airstrip lies nearly a mile from the ship - mile and a quarter, as the snowmobile scoots. Off the Des Groseilliers's starboard side, a cluster of fabric and plywood huts and shipping-container "offices" housing experiments and equipment have sprouted.

Groups of containers and huts have earned nicknames such as "Blue Bio" for marine biology, "Met City" for the meteorological teams, "Ocean City" for the oceanographers, and "Quebec" for the ice-studies team.

The ice station has the cluttered look of a work in progress. Teams of parka-encased scientists are erecting towers for weather instruments. Plywood sheets atop saw horses sag under the weight of equipment boxes. On the port side of the ship sit caches of oil drums - 900 barrels in all - to keep the icebreaker fueled through the winter.

Indeed researchers in their huts are not the only ones conducting experiments. This is the first time the Canadian Coast Guard has assigned an icebreaker to sit tight in Arctic Ocean ice for more than a year. The Des Groseilliers's role in the SHEBA project is seen as a test for providing support services for a growing number of Arctic research missions, according to Capt. Ren Turenne, the ship's skipper.

As a result, the icebreaker's skeleton crew faces its own set of unknowns. For example, the Des Groseilliers's steel hull is efficient at conducting heat and cold. Exposed to long periods of 40-below-zero temperatures, the hull might develop a thick sheath of ice below the water line, blocking intake ports that supply cooling water for the electric generators and seawater for conversion into drinking water.

Next spring's thaw could provide some excitement, he adds, as the ice floes crack, spread, and move. An oncoming floe could collide with the ice station's own shrinking floe. Or selective melting could turn the area around the icebreaker into a small lake.

"We might wake up one morning to find all of the huts gone or bobbing in the water," Captain Turenne says. "We're flying by the seat of our pants."