Water world?

Actor Kevin Costner knows there's no smooth sailing after a polar-ice meltdown. In Waterworld, his recent big-screen drama, there's water everywhere - but almost none to drink. Earth's landmasses have been completely submerged by the rising seas.

Pure movie fiction? Maybe not entirely. Some scientists warn that ice near Earth's Poles may indeed be melting.

A huge iceberg nearly the size of Rhode Island split off Antarctica's Larsen Ice Shelf last January. Weeks later, two 1,000-square-kilometer sections of the ice shelf disintegrated into icy fragments. "I was absolutely staggered by what I saw," recalls Mike Thomson of the British Antarctic Survey.

Meanwhile, a team of scientists at Earth's other end also found themselves on shaky ice. "The ice broke up constantly," recalls Will Steger, who led an expedition across the North Pole last spring. His team repeatedly dodged gaping abysses to avoid plunging into the icy Arctic Ocean.

Some scientists say this "polar meltdown" may be the first sign that Earth is heating up. "We could be in very serious trouble if this trend continues," Steger says.

Scientists estimate that a meltdown of as little as 10 percent of Antarctica's ice would raise sea levels around the globe by 4 to 9 meters (12 to 30 feet). Floods would submerge low-lying regions and turn coastal cities like New York and New Orleans into real-life underwater worlds.

Scientists first predicted in the 1970s that heat trapped in Earth's atmosphere could cause a polar meltdown. Many now believe that human activities are turning up the heat.

When we burn fossil fuels like coal and oil (to drive our cars, run televisions, and heat our homes), we add carbon dioxide ([CO.sub.2]) gas to Earth's atmosphere. Cutting down trees also makes [CO.sub.2] levels rise because trees normally soak Up [C0.sub.2] to make food. [CO.sub.2] in the atmosphere, explains climate researcher Judith Curry, acts like the glass ceiling of a greenhouse: It allows sunlight to pass through to warm the planet, but keeps the heat from escaping back into space. Scientists say higher [CO.sub.2] levels intensify this "greenhouse effect" - and could increase Earth's temperature.

GLOBAL GREENHOUSE

[CO.sub.2] levels are going up. Scientists say they've risen by 30 percent since the Industrial Revolution of the 18th and 19th centuries, when smoke-spewing factories sprung up in Europe and America. And Earth's temperature is rising too.

On the Antarctic Peninsula (see map, p. 14), the temperature has risen 2.5[degrees]C (4.5[degrees]F) over the past 50 years, says glacier scientist David Vaughan of the British Antarctic Survey. He believes that that warming is responsible for the recent shattering of the Larsen Ice Shelf

In the Arctic, explorer Steger says, the temperature was a "balmy" - 20[degrees]C (-4[degrees]F) - a full 25[degrees]C (45[degrees]F) warmer than normal - when his team set out. "The conditions were the warmest I've seen in 30 years," Steger observes.

Will this warm world become a Waterworld where you'll have to wear a wet suit to school?

Consider this: Over the past three years, satellite measurements have shown a sea-level rise of about a quarter inch worldwide, according to NASA scientists. "If nothing is done to reduce fossil-fuel pollution and global warming, sea levels will rise even more," says Richard Alley, a Penn State University geologist.

But even Alley admits that a polar meltdown would take time. The ice in Antarctica and the Arctic locks up nearly nine times the volume of water contained in all the world's rivers and lakes. "These are such big `ice cubes,'" he says, "it would probably take thousands of years to melt them."

Glacier scientist Charles Bentley of the University of Wisconsin doesn't think a meltdown will happen at all. "Even if warmer temperatures begin to melt polar ice," he says, "the excess moisture would most likely be redeposited as snow." In other words, the melted ice would evaporate into the atmosphere, refreeze, and fall as precipitation over the Poles.

Bentley thinks the recent calving, or breaking off, of icebergs from Antarctica is just "a natural part of a long-term cycle." In 1986, three icebergs - each bigger than this year's Rhode-I island-size chunk - broke free from the continent. One ice block may have melted as it drifted north to the tropics. But the other two remain frozen in shallow Antaretic waters.

The rest of the continent remains frozen too, assures Bentley. On the interior - where most of the ice lies - temperatures have not changed significantly over the past 30 years, he says.

Climate researcher Judith Curry says the recent Arctic "heat wave" may also be a climatic quirk rather than a sign of global warming. Globally, the average temperature has risen less than 1[degrees]C (1.8[degrees]F) over the past 100 years.

Still, many scientists say, that's a change worth noting because global warming could have consequences even more dire than coastal flooding. For example, a warmer world could mean destruction of ecosystems that cannot easily adapt to the heat; more extreme weather and tropical storms; changes in farm productivity; and more tropical diseases.

Governments around the world are beginning to heed the warnings. They are working on a "climate treaty" to reduce emissions of [CO.sub.2]. Most scientists agree that's a step in the right direction.

"If we go on assuming the world will respond slowly when we kick it," says geologist Alley, "we're probably wrong."

Cool

Planet

Every time we use electricity generated by burning fossil fuels (like oil and coal), we add heat-trapping carbon dioxide ([CO.sub.2]) gas to Earth's atmosphere. Eventually, some scientists say, the [CO.sub.2] buildup may warm the planet (and possibly melt polar ice!). The good news: You can help prevent global warming by cutting back on energy-consuming activities. Use this checklist to see how much [CO.sub.2] you add to the atmosphere - and how much you can cut back by changing your energy habits.

                     [CO.sub.2]
                      added to
Activity             atmosphere

* Watching            4.5g/hr
  TV
* Playing             4.5g/hr
  video games
* Leaving             2.7g/hr
  lights on
* Blow-drying           9g/hr
  your hair
* Traveling            11g/km
  by car
* Not recycling        10g/kg
  newspapers          newspaper
* Not recycling       200g/kg
  glass or            material
  plastic
Source: Climate Protection Institute, Oakland,
California