Rising seas 'to beat predictions'*

Sea level rise is fuelled by melting ice in Greenland and Antarctica

The world's sea levels could rise twice as high this century as UN
climate scientists have previously predicted, according to a study.

The Intergovernmental Panel on Climate Change proposes a maximum sea
level rise of 81cm (32in) this century.

But in the journal Nature Geoscience, researchers say the true maximum
could be about twice that: 163cm (64in).

They looked at what happened more than 100,000 years ago - the last time
Earth was this warm.

The results join other studies showing that current sea level
projections may be very conservative.

Sea level rise is a key effect of global climate change. There are two
major contributory effects: expansion of sea water as the oceans warm,
and the melting of ice over land.

In the latest study, researchers came up with their estimates by looking
at the so-called interglacial period, some 124,000 to 119,000 years ago,
when Earth's climate was warmer than it is now due to a different
configuration of the planet's orbit around the Sun.

That was the last time sea levels reached up to 6m (20ft) above where
they are now, fuelled by the melting of ice sheets that covered
Greenland and Antarctica.

'Robust' work

The researchers say their study is the first robust documentation of how
quickly sea levels rose to that level.

"Until now, there have been no data that sufficiently constrain the full
rate of past sea level rises above the present level," lead author Eelco
Rohling, of Britain's National Oceanography Centre in Southampton, said
in a statement.

Rohling and his colleagues found an average sea level rise of 1.6m
(64in) each century during the interglacial period.

Back then, Greenland was 3C to 5C (5.4F to 9F) warmer than now - which
is similar to the warming period expected in the next 50 to 100 years,
Dr Rohling said.

Current models of ice sheet activity do not predict rates of change this
large. However, they also do not include many of the dynamic processes
already being observed by glaciologists, the researchers said.

"The average rise of 1.6m per century that we find is roughly twice as
high as the maximum estimates in the IPCC Fourth Assessment Report, and
so offers the first potential constraint on the dynamic ice sheet
component that was not included in the headline IPCC values," explained
Dr Rohling.

Last year, a separate study found sea level rise projections could be
under-estimating the impact of human-induced climate change on the
world's oceans.