- WASHINGTON (Reuters) - A
big chunk of Antarctica has been melting for thousands of years and will
likely continue to melt until it swamps millions of miles (km) of coastland,
scientists said on Thursday. They said there was nothing anyone could
do about it -- and unlike other areas of Antarctica that were melting,
global warming was probably not to blame.
- "During the last ice age, the West Antarctic Ice
Sheet (WAIS) was 1,300 km (650 miles) more extensive than it is now in
the Ross Sea Embayment," Brenda Hall of the University of Maine,
who helped work on the study, said in an interview conducted by e-mail.
- "Our data would suggest that it has been retreating
ever since the end of the Ice Age -- probably the last 10,000 years."
- Reporting in the journal Science, they said its complete
collapse would raise the global sea level by 15 to 20 feet (5 to 6 metres).
- "Continued recession and perhaps even complete
disintegration of the WAIS within the present interglacial period could
well be inevitable," they wrote. The interglacial period is the time
between the last ice age, which ended 11,000 years ago, and the next one.
No one is sure when that will occur.
- Howard Conway, a geophysicist at the University of Washington
who led the study, said that although human-caused global warming might
be speeding up the process, there was little people could do to stop it.
- "Collapse appears to be part of an ongoing natural
cycle, probably caused by (a) rising sea level initiated by the melting
of the Northern Hemisphere ice sheets at the end of the last ice age,"
he said in a statement.
- "But the process could easily speed up if we continue
to contribute to warming the atmosphere and oceans."
- It is clear in some areas that the ice has been melting
since human activity such as burning fossil fuels started sending average
temperatures higher at the beginning of the century.
- But the causes in other areas that are melting have not
been so clear. Sometimes changes in currents, or in the way water washes
under the ice, can affect melting.
- Hall, Conway and colleagues made dozens of visits to
the West Atlantic Ice Sheet to measure the rate of melting. They looked
for clues about how big the ice sheet, which currently covers about 360,000
square miles (932,300 sq km), was in the past.
- Clues included deposits of penguin guano. "If the
penguins lived there, there couldn't have been any glacial ice at that
site or offshore in the ocean. They need open water," Hall said.
- They also looked at radar imaging of subsurface ice
structures and of ground-level ice. Ice weighs land down, and the earth
springs back when the ice melts. The researchers used carbon-14 dating
to tell how long ago beaches now 90 feet (28 metres) above sea level were
once under ice.
- Roosevelt Island in the Ross Sea provided other clues.
"It is an ice island -- a big block of ice that is so thick that
it rests on the sea floor, even though the surrounding ice is all floating,"
- "We used radar to look at the layers of ice inside
Roosevelt Island." Their measurements show it was once about 1,600
feet (488 metres) thicker.
- In another study, Ian Joughin and colleagues at the Jet
Propulsion Laboratory and California Institute of Technology in Pasadena
found water is pouring off the ice sheet in ice streams that slide quickly
to the ocean and break off into giant icebergs.
- Hall said she hoped the studies would not give ammunition
to critics of the global warming theory who say human activity is having
no effect whatsoever.
- "Although we say that the current retreat of the
ice sheet may not be the result of global warming, that doesn't mean that
global warming doesn't exist," she said.
- She noted that collapse of the WAIS would not be the
only effect of global warming. It could also shift ocean circulation
and weather patterns, bring drought, severe storms and the wider spread
of tropical diseases.