At The Whim of the Tide
Exploring the impact of the melting
Antarctic ice cap on global ocean levels
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Ryan Hunte
ENVR105AC
12/14/2009
N
ew York City, London,
Florida-under 10ft of water by
2050! Hype over melting of
the polar ice caps has flooded
the media since the Clinton
administration’s controversial rejection of
the Kyoto Protocol in 1997. A 2007 poll
indicated that 79% of Americans believe
human activity is the leading culprit behind
the shrinking ice caps. But the scientific
community and the public remain at odds
about exactly what’s causing the ice to
disappear. Some question whether the ice is
actually disappearing at all.
Former Vice President Al Gore, Nobel
Peace laureate and outspoken
environmental advocate, is renowned
for his initiative to inform the public
about the dangers of climate change.
Compliments of the BBC.
Part of the problem is gross
oversimplification by the media. What
we’re told by CNN and NBC, Al Gore and
Barack Obama falls dangerously short of the
full story. Often, discourse over the icy
dilemma is limited to a few vague
buzzwords: cap and trade, climate change,
global warming. While these phrases
encompass a part of the story, they’re far
from adequate if we’re to understand the
why and how of the ice melting mystery –
much less what ought to be done about it.
When discussing the melting ice caps, we
must first distinguish between the Arctic and
the Antarctic.
The planet’s North Pole is covered by the
Arctic Ocean. Due to its low sun exposure
and frigid climate, much of the Arctic Ocean
remains frozen year-round. This ice forms
the Arctic ice cap. Evidence suggests the
Arctic ice has receded more than 20% since
the 1970’s. But because Arctic ice cap is
really a giant pack of sea ice, if and when it
disappears, it will have no net impact on
global ocean levels.
Pen Hadrow, expedition leader of the Catlin
Arctic Survey, likened the effects of Arctic
ice on sea levels to that of an ice cube in a
glass of water. If an ice cube is placed in a
glass of water, the level of water in the glass
will remain constant even when the ice cube
melts. This is due to the phenomenon
known as displacement.
The Antarctic ice cap presents a different
story. Under the kilometers of ice, which
have built up over hundreds of millions of
years, is craggy, barren ground. That is,
Antarctica isn’t just solid ice. It’s solid ice
on top of rock.
So what? Why should we care if the
Antarctica is ice on the rocks as opposed to
ice on the sea? When it comes to the impact
of ice melting on ocean levels, this detail
makes a world of difference. Because
Antarctic ice that rests on rock doesn’t
influence ocean levels by displacement, as it
melts, sea levels will rise. This is where the
warnings of Al Gore transform from media
hype to science fact.
comprises 10% of the West Antarctic ice
sheet, has thinned by nearly 10m per year in
the last decade.
Not only are the ice caps melting – they’re
vanishing faster than ever before. Ten years
ago, Pine Island Glacier was melting at a
rate of 5m per year.
A study recently published in Science, a
research journal published by AAAS,
estimated the annual loss of Antarctic ice at
125 gigatons – “enough to raise sea level by
0.35 millimeters per year.” IPCC data
suggests that oceans have risen between
13cm and 18cm in over the past century, and
that levels may rise another meter by 2100.
Antarctica, which is covered in roughly
2,100m of ice, is of major concern because it
harbors 70% of the world’s fresh water. If
the entire continent melted, global ocean
levels would rise more than 60m.
Forecasting the Meltdown
When it comes to what’s causing Antarctica
to melt, there’s little that we know for
certain. But what we do know offers
evidence that the icy continent may be in
trouble.
A laser mounted on a satellite orbiting
hundreds of miles above the earth’s surface
allows scientists to record minute changes in
the thickness of the ice caps. The laser,
carried aboard ICESat - Ice, Cloud and land
Elevation Satellite – serves as a highly
precise altimeter by bouncing its beam off
the surface of ice. Using this technology,
researchers with the British Antarctic
observed that Pine Island Glacier, which
Fig. 1.1 Temperature changes on the Antarctic continent
from 1999 to 2009. Areas shown in shades of orange and
red have experienced warming over the past decade.
Compliments of the NASA Earth Observatory (January
2009).
A report published in Nature claims
“glaciers on the coast of East Antarctica are
thinning three times faster than scientists
previously believed.” Hamish Pritchard,
head researcher for the report noted “many
glaciers along the margins of Greenland and
Antarctic ice sheets are accelerating, and for
this reason contribute increasingly to global
sea-level rise.”
"This report provides a much more ominous
picture than we have had, and a depressing
prospect of the potential for sea level rise,"
observed Inez Fung, head atmospheric
scientist at UC Berkeley. "It's very much a
cause for worry."
A study published by Professor Eric Steig of
Washington University in the January
edition of Nature, an international science
journal, found that the surface
temperature of Antarctica
has increased 0.05°C per
decade from 1957 to
2006. Steig
attributes this to
rising ocean
temperatures,
which may be
hastening the
Antarctic
meltdown.
“Fortunately, East Antarctica is at present
the coldest of the continent's three regions,
and its ice sheet, which holds roughly 90
percent of Antarctica's ice, appears to be
mostly stable,” he began. “West Antarctica,
however, is a different story. That region is
changing rapidly in areas like the Pine
Island Glacier, and much vaster
expanses of ice are affected than
anywhere else on the continent.”
“So what makes West
Antarctica so different?” we
asked.
“The West Antarctic ice
sheet rests on a rocky bed
mostly below sea level, and
averages nearly a mile in
To give us the
thickness. A network of
lowdown on the
glaciers – ice streams if
Dr. Robert Bindschadler holds a B.S. in
situation, we
they're bordered by slowerAstronomy and Physics from the University
of Michigan and a Ph.D. in Geophysics from
interviewed Robert
moving ice on both sides –
the University of Washington.
Bindschadler,
channels large volumes of ice
Compliments of the US Antarctic Program.
whose many
from the inland center of the sheet
credentials include
to the relatively fast-flowing
Chief Scientist of the
perimeter, where the ice floats in
Hydrospheric and Biospheric
immense ice shelves.”
Sciences Laboratory at NASA, fellow of the
“West Antarctica has three subregions of
American Geophysical Union, and former
nearly equal size. One feeds the Ross ice
president of the International Glaciological
shelf; another feeds the Ronne ice shelf; and
Society. Bindschadler has led fifteen
a third feeds several smaller ice shelves that
Antarctic field expeditions, and has worked
dispense into the Amundsen and
on various glaciers around the world. He’s
Bellingshausen seas,” he explained.
published more than 150 scientific papers,
“Satellite observations show that the third
and has a glacier in Antarctica named after
subregion, with enough ice to raise sea level
him.
five feet, is changing most dramatically.
We first asked our resident expert a fairly
Two glaciers – both monstrously large –
straightforward question – why are we
dominate the discharge. These are the Pine
worried about Antarctica? Bindschadler’s
Island Glacier and the Thwaites Glacier.
answer was anything but simple.
Hundreds of miles long by tens of miles
wide and nearly a mile thick, they move at a
rate of more than a mile per year. When
satellite data began to accumulate in the
early 1990s showing that these two immense
glaciers were acting up, scientists became
deeply concerned. Calculations of the rate
of flow indicted that the bottom of the Pine
Island Glacier's floating ice shelf was
melting at a rate of more than 150 feet per
year. Thinning ice shelves are vulnerable to
collapse, of course. Even short of wholesale
disintegration, however, thinning almost
certainly results in acceleration of glacial
flow, and therefore in sea-level rise.”
“So why is West Antarctica in trouble?” we
asked.
“That’s a question scientists have been
trying to answer for decades,” he replied.
“While largely theoretical, the prevailing
hypothesis goes something like this. The
warmest water in the Southern Ocean, called
Circumpolar Deep Water (CDW), occurs at
depths of between 1,600 and 3,000 feet and
flows clockwise around Antarctica. Surface
waters, formed from sea ice melting during
the Antarctic summer, are less dense than
the CDW because they're fresher--less salty.
Bottom waters, below the CDW, are denser
because they're very cold. The CDW usually
stays well offshore, in the deep ocean,
because its upper boundary lies deeper than
the seafloor of Antarctica's continental
shelf,” Bindschadler remarked.
“To get to the ice, the warm CDW must first
get up onto the continental shelf. Increased
surface wind probably starts the process by
dragging surface water more rapidly around
Antarctica,” he noted. “The Coriolis force,
an effect of Earth's rotation, nudges that
Fig. 1.2 Circulation of dense CDW is postulated as the
fugitive behind melting in the West Antarctic.
Compliments of Natural History Magazine, Inc.
surface water away from the coast. The
CDW rises to replace the displaced surface
water. The stronger wind could stem from
an increase in the temperature difference
between the air over the continent and the
air over the surrounding ocean. Most of
Antarctica is warming more slowly than the
rest of the planet. Bigger temperature
differences cause stronger pressure
gradients, which cause stronger winds.”
“Back to the main story, once the salty
CDW is on the continental shelf, it stays
below the comparatively fresh surface water,
hugging the floor of the continental shelf.
But the continental shelf isn't flat; it slopes
down toward the continent, and it has
numerous valleys carved by glaciers during
past ice ages. The CDW sinks into the
valleys, which steer the warm water down
slope to the grounding lines of the glaciers.
Arriving at the glaciers' bases, the warm
CDW melts the ice it comes in contact with.
How much melting occurs depends on the
temperature difference between ice and
water. The CDW may be as warm as 5
Fahrenheit degrees above freezing. But at
the great depths that the CDW comes in
contact with the glaciers, the freezing point
of water decreases due to increased pressure.
Pine Island Glacier's grounding line lies
nearly 4,000 feet below sea level-deep enough to lower the
freezing point nearly another 3
degrees. Thus, the temperature
difference between the CDW and
the ice near Pine Island would be
about 8 degrees. That might not
sound like much, but it's enough
to cause the massive amounts of
melting.”
While Shepherd and Wingham, and
numerous others suggest that the melting of
the Antarctic poses clear danger to
humanity, their assertions are far from
uncontested.
The Controversy
While Antarctica’s net
loss of ice is multiply
attested throughout the
scientific community, so
too is the notion that
most of the continent is
actually cooling – and
growing.
A study published in
2002 found that
“No one has been able to confirm
“although previous
or discount the hypothesis,
reports suggest slight
because it’s very difficult to get
recent continental
equipment nearly a mile beneath
Dr. Ian Allison, Senior Principal
warming, our spatial
Research Scientist at the Australian
the ice,” Bindschadler noted,
Antarctic Glaciology Program,
analysis of Antarctic
“but for now that’s our best
conducted a study in 2002 that
meteorological data
showed Antarctica had cooled
guess.”
between 1966 and 2000.
demonstrates a net
Compliments of the AAD.
cooling on the Antarctic
A study conducted in 2007 by
continent between 1966
Professor Andrew Shepherd and Duncan
and 2000, particularly during summer and
Wingham of the Centre for Polar
autumn.”
Observation and Modelling highlights the
melting of Antarctic ice as a serious threat.
“The West Antarctic Ice Sheet (WAIS)
contains enough ice to raise global sea
levels by more than 5 m and, according
to altimetry and interferometry, one key
sector is in a state of rapid retreat…Such
a rise, were it to occur today, would have
tremendous societal implications. Even
a much more gradual rise would have
great impact.”
To comment on the controversy behind
Antarctic meltdown, we interviewed Head
of the Australian Antarctic Glaciology
Program Ian Allison. Allison not only
argues that Antarctica is cooling, but also
argues that sea ice losses in the west
Antarctica over the past 30 years have been
more than offset by increases in the Ross
Sea region– just one sector of east
Antarctica.
“Many of your colleagues in the field
believe the Antarctic – particularly the west
Antarctic – are quickly deteriorating.
What’s your take on the matter?” we asked
Allison.
“Sea ice conditions have generally remained
stable in the Antarctica,” Dr Allison noted.
“The media plays up only a small part of the
whole story. The fact of the matter is,
there’s no evidence of significant change in
the mass of ice shelves in east Antarctica or
any indication that its ice cap is melting.
Our study did find that 58 percent of
Antarctica cooled from 1966 to 2000.
Additionally, ice core samples taken in east
Antarctica by the Antarctic Climate and
Ecosystems Co-Operative Research Centre
show a 13% increase in the amount of ice
deposited annually compared to the 1950’s.”
“The only significant calvings in the
Antarctic have been in the west,” he
cautioned, “and these calvings really aren’t
that unusual. Ice shelves in general have
episodic carvings and there can be large
icebergs breaking off -- I'm talking 100km
or 200km long -- every 10 or 20 or 50
years.”
Public commentators like global warming
skeptic Michael Crichton tout the ambiguity
of Antarctic data as evidence that the ice
melting scare is a massive hoax.
While there may be validity to the assertion
that certain parts of Antarctica have cooled
over the last 50 years, the reason behind the
phenomenon is far from settling.
According to the British Antarctic Survey
(BAS), the hole in the ozone layer, created
by CFCs and other ozone-depleting
chemicals, has protected the Antarctica from
the effects of global warming. But this
protection isn’t permanent.
“Over the next 50 to 100 years, the ozone
hole will heal. At the same time,
greenhouse gases will rise, increasing the
intensity of warming in the area,” said Dr.
John Turner of the BAS. “In the next decade
or so we should see sea ice plateauing and
then decreasing massively if greenhouse
gases continue to increase.”
So What?
Even if ocean levels are rising a millimeter
or two per year, why should we care? After
all, a few feet of water by the end of the
century seems like a small price to pay for
our high-consumption lifestyles.
But the truth of the matter is that the today’s
models and forecasts are based on limited
data – and don’t take into account the
unprecedented rise in greenhouse gas
emissions that’s projected for the coming
decades.
And while a 0.88m increase in sea level by
2100 may not sound significant, a study
2007 funded by Environment and
Urbanization magazine found that 11% of
the world’s population – 634 million people
– may be affected by rising sea levels in the
coming century. The study also reported
that roughly two thirds of the world's cities
with populations in excess of five million
are located less than 10m above sea level –
making them vulnerable to changes in ocean
level in the future.
Certain cities, like Bengal, are already at
risk. A rise in sea level of just 40cm would
put 11% of Bangladesh’s coastal land under
water, displacing 7 to 10 million people.
In the fight against the Antarctic meltdown,
we must remember that rising sea levels is
only one of a host of symptoms of
greenhouse gas induced climate change.
Glacial melting, increased drought,
widespread famine, and mass species
extinction represent a fraction of the ill
effects that may befall us if clean energy,
cap and trade, green technology, and
international treaties don’t soon become
reality.
Putting off change may be bad for the
economy, too. A recent IPCC report
estimated that “doing nothing could lead to
damage costing as much as 20 percent of the
world’s gross domestic product.”
Think the economy’s bad when the growth
of the GDP slows to 2.5%? Imagine the job
market if climate change has its way.
Works Cited
Ananthaswamy, Anil. "Going, Going..." New
Scientist 202.2715 (2009): 28-33.
EBSCO Academic Premier. Web. 12
Dec. 2009.
Bindschadler, Roberd. "Ice on the Edge."
Natural History 117.9 (2008): 28-33.
EBSCO Academic Premier. Web. 12
Dec. 2009.
Doran, Peter T., John C. Priscu, W. B. Lyons,
John E. Walsh, Andrew G. Fountain,
Diane M. McKnight, Daryl L.
Moorhead, Ross A. Virginia, Diana H.
Wall, Gary D. Clow, Christian H.
Fritsen, Christopher P. McKay, and
Andrew N. Parsons. "Antarctic Climate
Cooling and Terrestrial Ecosystem
Response." Nature 415 (2001): 517-20.
Nature International Weekly Journal of
Science. Macmillan Publishers LLC, 13
Jan. 2002. Web. 12 Dec. 2009.
Kluger, Jeffrey. "Global Warming Heats Up."
Time Magazine. Time Magazine and
CNN, 26 Mar. 2006. Web. 12 Dec.
2009.
<http://www.time.com/time/magazine/ar
ticle/0,9171,1176980,00.html>.
Morales, Alex. "Oceans Rising Faster Than UN
Forecast, Scientists Say (Update2) -."
Bloomberg.com. Bloombery News
Corp, 18 June 2009. Web. 14 Dec. 2009.
<http://www.bloomberg.com/apps/news
?pid=20601124&sid=afmw1nT6inhA>.
Perlman, David. "Satellite Reveals Faster
Melting of Polar Ice." SFGate. San
Francisco Chronicle, 24 Sept. 2009.
Web. 12 Dec. 2009.
<http://www.sfgate.com/cgibin/article.cgi?f=/c/a/2009/09/23/MNM
M19R00D.DTL>.
Roberts, Greg. "Revealed: Antarctic Ice
Growing, Not Shrinking." The
Australian. 18 Apr. 2009. Web. 14 Dec.
2009.
<http://www.theaustralian.com.au/news/
revealed-antarctic-ice-growing/storye6frg6no-1225700046908>.
Shepherd, Andrew, and Duncan Wingham.
"Recent Sea-Level Contributions of the
Antarctic and Greenland Ice Sheets."
Science 315.5818 (2007): 1529-532.
AAAS, 16 Mar. 2007. Web. 12 Dec.
2009.
Talbot, David. "Measuring the Polar Meltdown."
Technology Review 110.6 (2007): 54-59.
EBSCO Academic Premier. Web. 12
Dec. 2009.