Antarctica's "Deep Impact" Threat
by Andy Caffrey

In the Spring issue of the Earth Island Journal we reported that British scientists feared the "critically unstable" Larsen B ice shelf "could break apart in as little as two years, triggering unpredictable weather events around the world."

On April 17, US government scientists reported that a 75-square-mile chunk of the Larsen ice shelf had broken loose and blamed the break-up on global warming. "This may be the beginning of the end for the Larsen ice shelf," said US National Snow and Ice Data Center research associate Ted Scambos.

On April 22, a report in Nature confirmed that the years 1990, 1995 and 1997 included the warmest days in the Northern Hemisphere in the last 500 years.

Meanwhile the mile-thick sheet of ice covering 85 percent of Greenland is vanishing at the rate of 2.5 centimeters a year and the Bering Glacier, the world's largest temperate glacier, has been retreating at a rate of 1 kilometer per year since 1990. Over the past 30 years, Western Arctic temperatures have risen 1 degree C.

Antarctica is covered by 90 percent of the world's ice. About 13.5 percent of that lies over West Antarctica, which is separated from the east by the Transantarctic Mountains. The Antarctic Peninsula extends from West Antarctica toward Tierra del Fuego. It is here that the greatest recorded warming on the planet has occurred in the last half century. In the last few decades, this region has warmed by 4.5 degrees F.

Every winter, Antarctica's four-foot thick sea ice expands to cover more open water. An area twice the size of the continental US becomes white with winter ice. This pushes the region's winter temperatures lower, as ice reflects more of the sun's energy back into space than do dark seas.

The ice on Eastern Antarctica is estimated to be between 11 and 17 million years old. In the west, it's mostly less than 600,000 years old. While the eastern ice sits in a bowl of mountains, most of West Antarctica's ice is anchored hundreds or thousands of feet below sea level: It is anchored on a mixture of glacier-pulverized rock and water which has the consistency of toothpaste.

In 1992, scientists discovered active volcanoes hidden under the ice of West Antarctica. According to their research (which was not published until 1993), one active volcano is four miles across and rests inside a 14-mile-wide caldera. Above these volcanoes, giant ice streams flow toward the ocean hundreds of times faster than the surrounding ice. The volume and width of these streams are several times that of the Amazon. If these streams were unleashed, they could collapse the surrounding ice sheet, possibly leading to its complete obliteration.

In the early 1960s, scientists began to ask what would happen if the West Antarctic ice sheet were to melt. They estimated that there would be a global 20- foot sea-level rise in an amazingly short period of time - 20 years or so. (After all, we are talking about nearly 10 percent of the world's ice.

Antarctica has a few giant ice shelves and several smaller ones that gird most of the continent (an ice sheet becomes an ice shelf when it expands into the ocean). The Larsen ice shelf runs up the east side of the peninsula while two other large ice shelves cover two enormous bays, the Ross and Ronne-Filchner. More than half of Antarctica's ice drainages pour into these two West Antarctic bays.

The bottom line: If Ronne or Ross begin to disintegrate, as Larsen is doing right now, then the plug for all of these ice streams will be removed (ice shelves surround 95 percent of Antarctica, retarding the outward motion of the ice streams), and the ice which sits above the continent (as opposed to that anchored below sea level) will move into the ocean, raising sea level.

No one knows how the bulk of West Antarctica's ice shelves are anchored. Are they anchored underneath by the islands they overrun, or are they anchored laterally to the Transantarctic Mountains? If the latter, a sea level increase from other global warming factors could lift the West Antarctica ice sheet enough to snap the "moorings" to the Transantarctic Mountains. One half of the world's population lives within areas that would be flooded by a 20-foot sea-level rise.

The August 1995 Scientific American reported that scientists in the Bahamas had discovered that the last Ice Age began 120,000 years ago with something called the "Madhouse Century." At that time, sea level was the same as it is now, CO2 levels were similar and global climate was just a little colder. Something happened to trigger a catastrophic 20-foot sea-level increase - immediately followed by a 50- foot decrease! - all in just 100 years. Then the Ice Age was off and running for 100,000 years.

If sea levels only 120,000 years ago were about the same as they are now, then the global ratio of ice-to-water was probably similar to what it is today. Which means that 12 percent of the world's ice suddenly melted, or broke up and melted. If the ice distribution was similar to today (90 percent over Antarctica; 10 percent over the rest of the planet), there is one persuasive and chilling explanation for the advent of a Madhouse Century: West Antarctica broke up.

If West Antarctica's ice is primarily anchored laterally, this could point to a possible trigger of most ice ages. CO2 appears to increase naturally during the 10,000 year interglacials. This could cause the oceans to expand until the mooring of West Antarctica breaks, triggering a Madhouse Century.

Because the continental ice flows would be thousands of feet thick, they would not melt away in the summer and would continue to reflect approximately 4 percent of the solar energy that hits the planet. This 4 percent reduction of solar heat would be enough to trigger a new ice age.

During the last ice age, sea levels fell more than 350 feet from current levels over a period of tens of thousands of years. This is largely because ice age cooling caused evaporated ocean water to freeze into continental glacier ice.

In the August 1995 Scientific American, Christina Stock reported how "for a geologic nanosecond - a century, in other words - some 120,000 years ago, the earth underwent climatic havoc." New findings show that sea level records, imprinted in limestone of the Bahama Islands, rose 20 feet above that of today and then plunged to at least 30 feet below modern levels. These erratic 100 years came at the close of the last interglacial era, a time when the climate was somewhat similar to ours.

"Maybe there is a threshold for warming that, once exceeded, starts to throw climate into a series of barrel rolls," speculates Paul J. Hearty, a geologist in Nassau. "If we continue to pump carbon dioxide into the atmosphere, are we going to warm the earth and trigger erratic sea level events like those that happened 120,000 years ago?"

Hearty calls this bizarre transition from an interglacial greenhouseto an ice age an example of the kind of "pulses of catastrophic change that dramatically reshape landscapes."

Hearty and his colleague A. Conrad Neumann of the University of North Carolina at Chapel Hill postulate that sea level was rising slowly as a result of normal interglacial greenhouse warming when something pushed the polar ice field beyond a critical point and ice surged into the ocean - an idea proposed in 1980 by J. T. Hollin of the University of Colorado at Boulder. When the seas receded, presumably due to rapid ice formation at the poles, sand from lagoons in the Bahamas blew over forests and entombed now-fossilized palm trees in dunes. Hearty and Neumann reason that the water must have withdrawn suddenly, followed by raging storms.

Researchers agree that sea level rise has quickened during the past century, along with atmospheric warming, and that coastal erosion and flooding are a reality. Ancient and modern data suggest that half of the planet's population - those people living in coastal areas - may be the first to feel the impacts of the next Madhouse Century.

Andy Caffrey is the director of Climate Action NOW!, PO Box 324, Redway, CA 95560, (707) 923-2114.