New
Study Finds 3-4 Meter
Sea Level Rise From
Antarctica May be Imminent
3
October, 2014
Ocean
stratification. A condition characterized by the separation of layers
of water of different temperatures and chemical make-up. A condition
that has serious impacts to the geophysical nature of the worlds
oceans, to the ability of oceans to support life, and to the
stability of the vast glaciers of Antarctica — whose faces plunge
as deep as hundreds of feet into the Southern Ocean.
In
the Antarctic, today, what we see is a cold surface layer and a
heating bottom layer. The cold surface layer is fed by an expanding
pulse of chill, fresh water issuing from the melting glaciers of
Antarctica. Over the years it has become more uniform, sequestering
cold near the surface as warmth builds up in the depths below. The
deeper hot layer is fed by warmer water issuing in from the tropics
and heated to temperatures not seen for tens of thousands of years.
This hot water bears a heavy burden of salt. So it is denser and it
dives beneath the expanding fresh water layer. The insulating fresh,
cold water layer prevents mixing between the bottom layer and the
surface. Such mixing would cool the bottom layer. But instead the
heat builds and builds and builds.
(Antarctica — visual difference in ice mass between now [right] and last glacial maximum [left]. By mid century, atmospheric greenhouse gas concentrations driven by humans could be high enough [550 ppm CO2e+] to melt all the remaining ice upon this now-frozen continent. Image source: NASA/Goddard Space Flight Center.)
Ocean
currents bring the deep, hot water in contact with the base of
Antarctica’s massive glaciers. And this intensely focused heat
engine goes to work to rapidly melt the ice.
It
is this condition of ongoing and intense melting of the ice sheet’s
bases that terminate in faces of ice cliffs, hundreds of feet high
and deeply submerged in the sea, that is driving the irreversible
collapse of many glaciers in Antarctica. Already, due to this
irreversible fall, the entire flank of West Antarctica is under
collapse — locking in at least three feet of sea level rise from
this region alone going forward.
From
Nature Communications:
“The
reason for the layering is that global warming in parts of Antarctica
is causing land-based ice to melt, adding massive amounts of
freshwater to the ocean surface,” said ARC Centre of Excellence for
Climate System Science researcher Prof Matthew England an author of
the paper.
“At
the same time as the surface is cooling, the deeper ocean is warming,
which has already accelerated the decline of glaciers on Pine Island
and Totten. It appears global warming is replicating conditions that,
in the past, triggered significant shifts in the stability of the
Antarctic ice sheet.”
The
last time this happened was 14,000 years ago as the Earth slowly
warmed out of the end of the last ice age. But the result was
anything but gradual:
“Our
model simulations provide a new mechanism that reconciles geological
evidence of past global sea level rise,” said researcher UNSW ARC
Future Fellow Dr Chris Fogwill.
“The
results demonstrate that while Antarctic ice sheets are remote, they
may play a far bigger role in driving past and importantly future sea
level rise than we previously suspected.”
“The
big question is whether the ice sheet will react to these changing
ocean conditions as rapidly as it did 14,000 years ago,” said lead
author Dr Nick Golledge, a senior research fellow at Victoria’s
Antarctic Research Centre.
These
are critical questions. Ones that have serious impacts for the more
than 700 million people now living within 10 meters of current sea
level.
(Antarctic Ice Shelf thickness changes. Note the thinning of almost all the ice shelves along the margin of Antarctica. Ice shelves anchor interior ice, keeping it from rushing out through deep channels into the Southern Ocean. Rapidly thinning ice shelves is a precursor to glaciers rushing toward the sea. Image source: Nature Pritchard et al. 2012)
To
this point it is worth noting that the pace of warming 14,000 years
ago was on the order of 0.05 degrees Celsius each century. The
current pace of human-driven warming over the past century was 20
times faster. This century, the warming is predicted to be as much as
500 times faster (3-5 C warming by 2100). So the question may we be —
will Antarctica respond as ‘slowly’ as it did at the end of the
last ice age? Slow
as in ice outbursts that lead to sea levels rising by as much as 14
feet during one century.
Links:
(Hat
Tip to Colorado Bob)
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