PARIS (AFP): Billions
of tonnes of meltwater flowing into the world’s oceans from the Greenland and
Antarctic ice sheets could boost extreme weather and destabilise regional
climate within a matter of decades, researchers said on Wednesday.
These melting giants,
especially the one atop Greenland, are poised to further weaken the ocean
currents that move cold water south along the Atlantic Ocean floor while
pushing tropical waters northward closer to the surface, they reported in the
journal Nature.
Known as the Atlantic
Meridional Overturning Circulation (AMOC), this liquid conveyor belt plays a
crucial role in Earth’s climate system and helps ensures the relative warmth of
the Northern Hemisphere.
“According to our
models, this meltwater will cause significant disruptions to ocean currents and
change levels of warming around the world,” said lead author Nicholas Golledge,
an associate professor at the Antarctic Research Centre of New Zealand’s
Victoria University of Wellington.
The Antarctic ice
sheet’s loss of mass, meanwhile, traps warmer water below the surface, eroding
glaciers from underneath in a vicious circle of accelerated melting that
contributes to sea level rise.
Most studies on ice
sheets have focused on how quickly they might shrink due to global warming, and
how much global temperatures can rise before their disintegration — whether
over centuries or millenia — becomes inevitable, a threshold known as a
‘tipping point.’
But far less research
has been done on how the meltwater might affect the climate system itself.
“The large-scale
changes we see in our simulations are conducive to a more chaotic climate with
more extreme weather events and more intense and frequent heatwaves,” co-author
Natalya Gomez, a researcher in the Department of Earth and Planetary Sciences
at McGill University in Canada, told AFP.
“By mid-century,” the
researchers concluded, “meltwater from the Greenland ice sheet noticeably
disrupts the AMOC,” which has already shown signs of slowing down.
This is a “much shorter
timescale than expected,” commented Helene Seroussi, a researcher in the Sea
Level and Ice Group at the Jet Propulsion Laboratory in California, who was not
involved in the study.
The findings were based
on highly detailed simulations combined with satellite observations of changes
to the ice sheets since 2010.
One likely result of
weakened current in the Atlantic will be warmer air temperatures in the high
Arctic, eastern Canada and central America, and cooler temperatures over
northwestern Europe and the North American eastern seaboard.
The Antarctic and
Greenland ice sheets, up to three kilometres thick, contain more than
two-thirds of the planet’s fresh water, enough to raise global oceans 58 and
seven metres, respectively, were they to melt completely.
Climate change
‘increased frequency of disasters’
Besides Greenland, the
regions most vulnerable to global warming are West Antarctica and several huge
glaciers in East Antarctica, which is far larger and more stable.
In a second study
published on Wednesday in Nature, some of the same scientists offered new
projections of how much Antarctica will contribute to sea level rise by 2100 —
a hotly debated topic.
A controversial 2016
study suggested the continent’s ice cliffs — exposed by the disintegration of
ice shelves that jut out from glaciers over ocean water — were highly
vulnerable to collapse, and could lead to sea level rise of a metre by
century’s end.
That would be enough to
displace up to 187 million people around the world, especially in populous
low-lying river deltas in Asia and Africa, research has shown.
But the new study
challenges those findings.
“Unstable ice-cliffs
were proposed as a cause of unstoppable collapse of large parts of the ice
sheet,” said lead author Tamsin Edwards, a lecturer in geography at King’s
College London.
“But we’ve re-analysed
the data and found this isn’t the case.”
Both of the news
studies, Edwards told AFP, “predict a most likely Antarctic contribution of 15
centimetres” by 2100, with an upward limit of about 40 cm.
A special report on
oceans by the UN’s Intergovernmental Panel on Climate Change (IPCC), due out in
September, will offer a much anticipated estimate of sea level rise.
The IPCC’s last major
assessment in 2013 did not take ice sheets — today seen as the major
contributor, ahead of thermal expansion and glaciers — into account for lack of
data.
