New Scientist Magazine, Jonathan Knight
A GROUP of islands off Papua New Guinea that are supposedly being
drowned because of global warming are in fact safe, New Scientist
has learned. Contrary to recent reports, climate change and earthquakes
are not to blame for recent floods. The flooding is a temporary
climate phenomenon, and a large earthquake in mid-November actually
raised the land by a few centimetres.
Early last
year, seawater invaded low-lying agricultural land on the main
island of the Duke of York group. Scientific officers of the United
Nations Development Programme in Port Moresby concluded that the
island was sinking by between 10 and 15 centimetres a year.
Officials
immediately said they would relocate the 20,000 islanders and
last week announced plans to move the first 1000 from the soggiest
areas. Some media coverage blamed global warming for the flooding
and called the relocation a "dress rehearsal" for coastal
dwellers worldwide. Reports put the rate of sinking at 30 centimetres
per year.
"Our
measurements quite clearly show that hasn't happened," says
geologist Paul Tregoning of the Australian National University
in Canberra. He and his colleagues used readings from Global Positioning
System satellites to measure the island's elevation in 1995 and
again in November this year.
He says the
island has subsided no more than 12 centimetres in those five
years and actually rose by 3 centimetres during the 16 November
quake. Even in the tectonically active South Pacific--where each
year islands rise and fall by tiny amounts--these movements are
extreme. But they are still much smaller than the reported sinking
rate.
A more likely
cause of flooding is the temporary 25-centimetre rise in average
sea levels in the region since early 1998. High atmospheric pressure
off South America during the 1998-99 La Niña caused sea
levels in the Western Pacific to rise above normal. A coincidental
series of severe storms may have made matters worse by eroding
sand bars and beaches, says Steve Saunders of the Rabaul Volcano
Observatory on the neighbouring island of New Britain.
"The
way the media reported the sinking story would make a good story
in itself," Saunders told New Scientist. Most of the islands'
60 square kilometres were never threatened. They lie tens of metres
above sea level and are surrounded by sheer cliffs.
Global warming
has little to do with flooding on any South Pacific islands, says
Chalapan Kaluwin, Climate Change Officer with the South Pacific
Regional Environment Programme in Samoa. "It is difficult
to talk about global warming at this time, because the climate
variability is so big." Melting polar ice is expected to
raise global sea levels by an average of 5 to 10 centimetres by
2025, but Kaluwin says the best estimate of the current rise in
the South Pacific is only 1 millimetre per year. "The sea
level is going to rise," he says, "but it will take
a lot of years."
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