Rising oceans threaten to destroy ecosystems

By Claude Morgan

The seas are rising nearly one-tenth of an inch each year, fed by rivers of melting glaciers and ice sheets around the globe, according to scientists at the United States Geological Survey. At the current rate of melting, the seas could rise another foot over the next 50 years. Iceland's glaciers could disappear by 2200. That event alone could raise sea levels by 20 feet.

Every 100,000 years or so, the earth settles in for an ice age, taking its cue from changes in its orbit around the Sun. During long, elliptical orbits, the earth cools, and water is stored on the continents in the form of ice. Sea level falls. During shorter, circular orbits, the earth warms up, and the ice returns to the sea, causing a rise in sea level. These warming spells, called interglacial periods, typically last about 10,000 years.

"We're about two thirds of the way through an interglacial period, right now," said Richard Williams, an oceanographer with the USGS at Woods Hole, Massachusetts. The current warming spell is called the Holocene Epoch.

Fossil records and other scientific evidence show that many times that amount of ice has succumbed to the cosmic dance of hot and cold in the past. During the last interglacial period, for instance, most scientists now agree, sea levels rose 20 feet above where they are today.

But just how much of this warming cycle is natural and how much is man-made has scientists locked in their own ebb and flow: Most scientists believe that human contributions to the greenhouse effect contribute to global warming and sea-level rise; a few are cool to the idea.

Evidence found in deep layers of polar ice reveals that ancient levels of atmospheric CO2 were much lower than present levels. "We've seen a 30 percent increase of those levels since the last interglacial," says Williams. "So, I'd have to say, at this point, we're contributing to global warming and accelerating the rise in sea levels."

Pat Michaels, a professor of environmental studies at the University of Virginia, disagrees. He says human contributions to greenhouse gasses notwithstanding, human activity pales in comparison to cosmic cycles.

"The amount of sea-level rise from human contributions in the 20th century has been grossly exaggerated," argues Michaels.

Whichever scientific argument prevails, however, nearly all scientists agree that this is one tide we won't be turning back. Instead, many of them say, we should prepare for a slow and orderly migration inland - away from the coasts, taking special care to protect delicate ecosystems along the way.

One half of the land directly impaired by sea-level rise is wetlands," said Jim Titus, project director of sea level rise at the U.S. Environmental Protection Agency. "Fortunately, this is one impact of global warming where we can actually do some very rational things. But first we need to get everybody rowing in the same direction."