collapse of the Western Antarctica ice sheet is already under way and
is unstoppable, two separate teams of scientists said on Monday.
glaciers' retreat is being driven by climate change and is already
causing sea-level rise at a much faster rate than scientists had
loss of the entire western Antarctica ice sheet could eventually
cause up to 4 metres (13ft) of sea-level rise, devastating low-lying
and coastal areas around the world. But the researchers said that
even though such a rise could not be stopped, it is still several
centuries off, and potentially up to 1,000 years away.
two studies, by Nasa and the University of Washington, looked at the
ice sheets of western Antarctica over different periods of time.
Nasa researchers focused on melting over the last 20 years, while the
scientists at the University of Washington used computer modelling to
look into the future of the western Antarctic ice sheet.
both studies came to broadly similar conclusions – that the
thinning and melting of the Antarctic ice sheet has begun and cannot
be halted, even with drastic action to cut the greenhouse gas
emissions that cause climate change.
also suggest that recent accumulation of ice in Antarctica was
large sector of the western Antarctic ice sheet has gone into a state
of irreversible retreat. It has passed the point of no return,”
Eric Rignot, a glaciologist at Nasa and the University of California,
Irvine, told a conference call. “This retreat will have major
consequences for sea level rise worldwide.”
two studies between them suggest sea-level rise will be far greater
than envisaged by the United Nations’ IPCC report earlier this
year. The IPCC forecast on sea-level rise did not factor in the
melting of the western Antarctica ice sheet.
Nasa study, to be published in Geophysical Research Letters, studied
the retreat of six glaciers in western Antarctica that are already
the major drivers of global sea-level rise.
of those glaciers, Pine Island, retreated 31km at its centre from
1992-2011. Rignot said all six glaciers together contained enough ice
to add an additional 1.2m (4ft) to sea levels around the world.
the University of Washington study, which will be published in the
journal Science, researchers used detailed topography maps, airborne
radar and computer modelling to reach greater certainty about the
projected timeline of the ice sheet collapse.
study honed in on the Thwaites glacier – a broad glacier that is
part of the Amundsen Sea. Scientists have known for years that the
Thwaites glacier is the soft underbelly of the Antarctic ice sheet,
and first found that it was unstable decades ago.
University of Washington researchers said that the fast-moving
Thwaites glacier could be lost in a matter of centuries. The loss of
that glacier alone would raise global sea level by nearly 2ft.
also acts as a dam that holds back the rest of the ice sheet. Once
Thwaites goes, researchers said, the remaining ice in the sheet could
cause another 10 to 13ft (3-4m) of global sea-level rise.
thinning we are seeing is not just some temporary trend. It is really
the beginning of a larger scale collapse that is likely to play out
over a two to 10-century range,” Ian Joughin, a University of
Washington glaciologist, told The Guardian.
said the retreat would begin slowly, resulting in sea-level rise of
less than 1mm a year for a couple of hundred years. But “then boom,
it just starts to really go,” Joughin said.
under the worst-case scenario currently envisaged, the collapse of
the entire ice sheet is about 200 years off – and the collapse
could be as far away as 1,000 years, depending on future warming.
collapse is inevitable, the scientists said. Joughin put the most
likely timeframe at between 200 and 500 years.
two teams of scientists used airborne radar and satellites to map the
layers of ice down to the sea bed, and to study the rate of glacier
movement. The Nasa team also drew on observations stretching back 40
so, Rignot said he was taken aback at how fast change was occurring.
system, whether Greenland or Antarctica, is changing on a faster time
scale than we anticipated. We are discovering that every day,”
are also finding that the causes of the ice loss are highly complex –
and that it is not just due to warmer temperatures causing surface
melting of the ice.
papers said the contact between the glaciers and the relatively
warmer water at the ocean depths was the main driver of the
said that even drastic action to cut greenhouse gas emissions that
cause climate change could not prevent the collapse.
feel this is at the point where even if the ocean is not warming up,
is not providing additional ocean heat, the system is in a sort of
chain reaction that is unstoppable,” he told reporters on a
only thing that could hold the glaciers back would be a large hill or
big mountain that could block the retreat, Rignot said. But there is
none, he said, “So we think it is not going to be stoppable.”