TIME MACHINES AND ICEBERGS
What these icy time travelers have discovered has generated intense interest -- and controversy. In particular, their studies have shown that the amount of carbon dioxide in Earth's atmosphere has risen rapidly in the industrial era. That's a concern because many researchers believe carbon dioxide acts as a global warming gas, trapping heat near the planet's surface and causing long-term changes in climate. While the change of weather could be good news for some people, it could be disastrous for others. If warmer temperatures were to melt Antarctica's ice caps, for instance, researchers estimate that the global sea level would rise an average of 230 feet, flooding most coastal cities and drowning places like New York, London, and Hong Kong.
Some scientists say it's too early to see such signs of global warming. But others say there is evidence -- and it can be found in the enormous icebergs that are breaking free from Antarctica every year.
In August, 1992, for instance, a monster iceberg 20 times bigger than Manhattan sheared off from an Antarctic glacier jutting into the Bellingshausen Sea. In 1999, it drifted into shipping lanes off Argentina, prompting a worldwide warning to ships to stay clear of the 41-mile-long, 13-mile-wide slab, which rises 180 feet out of the sea and reaches a depth of 900 feet. Maritime officials fear the mother berg may eventually give birth to hundreds of calves, each of which could pose a substantial threat to cargo and passenger vessels. "We're watching it very closely," says one U.S. official, who notes that everything from satellites to rowboats is being used to track the floe.
Many researchers believe more giant bergs are on their way as Antarctica's massive ice sheets melt back due to warmer temperatures, but that could take a very long time. Scientists recently estimated that it could take 7,000 years for the giant West Antarctic ice sheet to eventually disappear. And other researchers note that while some ice sheets are shrinking, others appear to be growing -- for reasons nobody yet understands.