A Tale of Two Ice Caps: As Arctic Ocean Heads Toward Ice-Free Summers, New Study Shows Human Warming Takes Out 56% of Antarctic Sea Ice by 2050
3
March, 2014
Thus
far, the Arctic has been ground zero for human-caused climate change.
A combination of sea ice melt, albedo loss, a warming ocean that
transports heat beneath a melting ice cap, regions of Jet Stream
retreat into the far north, and an overburden of greenhouse gasses
near the pole, among other factors, have all resulted in a very rapid
pace of local warming.
(Global
surface temperature anomaly over the last month features a high
degree of, very visible, Arctic heat amplification. Most global
warming models show the Arctic warms rapidly first under human
warming. Then, as second stage warming progresses, heat begins to
spike over other regions of the globe. Image source: NOAA
ESRL.)
While
global warming totals about .8 C above the 1880s average, about 1/6th
the difference between now and another ice age, but on the side of
hot, Arctic
warming has pushed above 3.0 C during the same time period.
And as the Arctic is warming four times as fast as the rest of the
globe, many of human climate change’s most extreme impacts are now
visible there.
The
Arctic’s Massive and Dramatic Loss of Sea Ice
A
primary measure of Arctic warming has been sea ice melt. And Arctic
sea ice melt during the past few decades has been nothing if not
dramatic. By end of summer 2012, a time when sea ice melt is most
intense, area and extent totals had fallen more than 50% below their
1979 measurements. Meanwhile, Arctic sea ice volume, a measure of
area + thickness, had fallen by as much as 80%. These losses are
dramatic and raise the possibility for ice free summers, if the
weather conditions line up, during a period between now and 2030.
(Arctic
death spiral showing sea ice volume measurements for all months from
1979 through early 2013. Image source: Skeptical
Science.
Data source: PIOMAS.)
Thin
Ice Over Warming Water
As
hinted at above, the Arctic has a number of unique characteristics
that make it vulnerable to rapid warming in the context of a more
slowly warming globe. And chief among these is geography — warmer
continents surrounding a mostly frozen ocean.
A
lion’s share of the northern polar ice cap area is composed of sea
ice. By area, even after the stunning losses seen since 1979, the sea
ice cap composes about 10.5 million square kilometers on average.
Greenland, in contrast, only boasts an ice sheet of around 2 million
square kilometers. This large layer of ice provides an amazing amount
of cooling just due to its white, reflective properties. In the past,
this albedo has helped to maintain a zone of very cold air centered
almost directly over the pole.
But
this Arctic system of cold amplification and northern refrigeration
has a major Achilles heel. For the sea ice sits upon an ocean that is
much closer to the melting point of water than any frozen land mass.
Furthermore, all ocean systems are connected and, to one degree or
another, readily transport heat.
In
the context of human-caused warming, the majority of northern polar
ice area is little more than a relatively thin layer sitting atop an
ocean that is rapidly collecting atmospheric heat. A context that can
result in rather dramatic consequences. In short, what this means is
that northern polar ice sheet inertia isn’t quite so strong as was
previously hoped.
A
warming ocean eats away at the bottom ice. And as the thin, frozen
ice layer of white, reflective ice is, at first gradually, and then
more rapidly, replaced by dark, absorptive ocean the Arctic
refrigerator breaks down and, increasingly, turns into a heat
amplifier. A quickening pace of albedo loss means an even more rapid
pace of warming for the ocean waters below. As warmth concentrates,
more feedbacks come into play. Greenhouse gasses like methane and CO2
become liberated from the ice and also go to work in setting off
warming. These
feedbacks work in concert and, for a time, the Arctic heat rapidly
amplifies.
Arctic
heat amplification is now plainly visible in winter months when heat
absorbed by a mostly ice-free Arctic Ocean during summer radiates up
through thin and crack-riddled ice. In this way, heat bubbling up
through the ice displaces cold, Arctic air southward, sparking off
severe weather. An ongoing event that was particularly extreme during
the winters of 2012-2013 and 2013-2014 when Arctic air first fled
south over Europe and then the central and eastern United States (see
polar vortex collapse).
An
extended period of heat amplification has been the story of Arctic
warming ever since the world began to heat up during the 1880s. A
more moderate spurt of sea ice loss coincided with the growing Arctic
warmth from the 1920s to the 1950s before stalling in the 60s and
70s, only to resume with a vengeance during the 1980s. Today, the
extreme of Arctic heat amplification results in a number of rather
severe knock-on effects that threatens everything from even larger
Arctic greenhouse gas releases (methane, CO2) and severe changes to
the Jet Stream that may well wreck the periods of relatively stable
weather human beings in the north have been used to for 10,000 years
running.
Antarctic
— Vast Continental Ice Sheets Surrounded By Oceans
Moving
southward into the still frozen austral regions, we find a geography
and related pace of climate change that is markedly different. Here
the vast glaciers pile atop a Continent that has now been buried and
frozen for millions and millions of years. The cold is locked into
ice sheets that reach thousands of feet in height, cover an area of
nearly 14 million square kilometers, and plunge deep into the
long-frozen Earth. If the ice in the Arctic is merely a thin facade
covering warmer oceans, the Antarctic ice is a thick fortress atop
adamant and frozen earth.
The
degree of inertia this represents for human-caused climate change is,
therefore, much greater than what we see up north. And though the
Antarctic fortress is far from impenetrable to the radically strong
assaults of human warming, it will resist their insults for longer,
giving way its great piles of ice in a more ablative fashion with,
likely, even more stark and shocking results.
This
densely frozen geography coming into conflict with human-caused
warming has resulted in far-reaching, though less visible, impacts.
Overall, largely due to the heat-insulation effect of Antarctica,
southern hemisphere warming has progressed far more slowly than
warming in the north. Here the battle is one of inches in which
regions closer to the equator, such as Australia and the equatorial
oceans, show the highest rates of warming. Meanwhile, Antarctica has
remained, for the most part, a bastion of cold with increasingly
intense wind fields isolating it from the more rapidly warming
regions. In this case, and in contrast to the Northern Hemisphere Jet
Stream, the upper level winds surrounding the South Pole have
strengthened even as they have slowly receded.
(Antarctica
surrounded by storms on March 2 of 2014 as a combination of austral
summer and human warming shove the Southern Hemisphere Jet Stream
toward the pole. Image source: Lance-Modis.)
Such
a recession resulted in very hot, dry weather for southern Australia
as equatorial heat shoved the strong winds and related storms ever
southward. Meanwhile, increased rates of evaporation held in check
the benefits of equatorial rain expansion into northern regions. Only
the occasional challenge to this new, retreating Jet Stream, breaks
the pattern of expanding drought in the south with extraordinary
precipitation and storm events. And so Australia has suffered a
series of worst droughts and fires on record interrupted by brief but
very intense rain events over the past decade.
While
the vast ice sheets of Antarctica have, so far, served as a buttress
against atmospheric warming even as the Jet Stream retreated
southward, heat in the ocean again went to work. Though mostly
protected by vast and frozen continental lands to the west, the more
northerly segment of East Antarctica featured large sections of
submerged continents upon which rested immense, sea terminating ice
sheets. Some of these great ice sheets had sections submerged
hundreds of feet below sea level. And though the surface waters only
gradually warmed, deeper down, the story was much different.
The
endless calving of Antarctica’s glaciers sends off thousands of ice
bergs from the shores of Antarctica each year. This massive calving
cools the surface waters near Antarctica through both the melting of
these frozen hills and mountains as well as the chilling effect they
have on nearby air currents. As such, cold waters continually flow
out from Antarctica. But even these waters have been impacted by
human caused climate change, grudgingly increasing in temperature
over the decades.
(Pine
Island Glacier calves into the Amundsen Sea. A recent study found
this large ice sheet was in the first stages of irreversible
collapse. Image source: iSTAR-NERC.)
If
the cold surface waters surrounding Antarctica have warmed only
slowly, the story of the depths is somewhat different. Down-welling
warmer and saltier waters contacting the Antarctic Circumpolar
Current create a growing pool of warmth extending to the Antarctic
Continental Shelf boundary. There, water circulation dynamics cause
the warm water in the abyss to up-well even as it contacts the ocean
terminating polar ice sheets.
The
warm water thus eats away at the undersides of these ice sheets,
causing increasing instability in some of the most vulnerable regions
of West Antarctica. This heat transfer from the ocean depths has set
off a significant erosion in a number of very large ice sheets and is
now spurring the massive Pine Island Glacier (PIG) into an
unstoppable rush to the sea.
Models
Show Antarctic Sea Ice to Rapidly Decline
through Mid Century
If
Antarctic warming has been more subtle than the explosive heat
amplification of northern regions, it is no less ominous. At the very
least, it resulted in locking in 1-2 meters of sea level rise through
irreversible ice sheet collapse spurred by warm water upwelling and
now puts at risk many more meters of eventual increases to follow.
But,
at the surface of the waters, despite a period of slowly rising
warmth, the buffer zone of Antarctic sea ice has remained somewhat
stable since 1979, even showing periods of moderate increase in
overall area and extent. As described above, this is in marked
contrast to a stunning collapse of Northern Hemisphere sea ice. A
contrast that has served as foil for much debate over the ongoing
impacts of human warming even as it was exploited as fodder by
climate change deniers, when they weren’t out chasing the most
recent snowstorm.
(Antarctic
sea ice area anomaly since 1979 shows a slight increase in overall
coverage, primarily due to a counter-trend increase in Ross Sea ice
coverage. New studies show Antarctic sea ice is now set to rapidly
decline. Image source: Cryosphere
Today.)
Looking
more closely, though, one finds that the current expansion of
Antarctic sea ice may well be very precarious. For of the three
embayments containing Antarctic sea ice only one — the Ross Sea —
has shown sea ice growth in recent years. The other two have either
remained stable or shown slow recession.
Polar
researchers had attributed the moderate net expansion of southern sea
ice to a combination of increasingly strong winds spreading out Ross
ice flows during winter, a freshening of surface waters through the
ongoing melt of Antarctica’s ice sheets that increases the melt
temperature of ice and thus encourages its formation, and to changes
to ocean currents and rates of precipitation. Now, a new study
conducted by researchers at the Virginia Institute of Marine Science
has found that this relative period of Ross sea ice stability and
growth is about to end.
Warmth
About to Crash Through Antarctica’s Gates
The
various fragile conditions that have conspired to expand Ross Sea ice
are now about to collapse under an onrush of increasing temperatures.
For according to a new study entitled The
Effects of Changing Winds and Temperatures on the Oceanography of the
Ross Sea During the 21rst Century high
resolution climate models show both increasing temperatures and
rapidly melting ice in this critical and climatologically sensitive
region under a regime of business as usual fossil fuel emissions.
According
to the study’s authors:
We examined the effects of projected changes in atmospheric temperatures and winds on aspects of the ocean circulation likely important to primary production using a high-resolution sea ice–ocean–ice shelf model of the Ross Sea. The modeled summer sea ice concentrations decreased by 56% by 2050 and 78% by 2100.
In
short, the bounding Jet Stream, the insulating continental Antarctic
ice, and the cold surface waters surrounding the continent can’t
keep out an ever increasing level of human-caused warming
indefinitely. Over the coming decades this warmth will pulse higher
in the region surrounding Antarctica with profound impacts to sea
ice, resulting in a more than 50% reduction by 2050 and a 78%
reduction by 2100.
The
study also found that:
The ice-free season also grew much longer, with the mean day of retreat in 2100 occurring 11 days earlier and the advance occurring 16 days later than now.
In
essence, the spring and summer melt season throughout the Antarctic
region was shown to extend nearly one month longer than today’s
period of melt and warmth. Such an expansion of heat intensity and
duration will have profound impacts not only for sea ice, but for
land ice and for life in the oceans as well.
Mixing
Layers Reduced, Large Phytoplankton Blooms to Follow
Perhaps
less visible but somewhat more ominous are ocean changes that are
projected as Antarctic sea ice goes into rapid decline. Study authors
found that ocean mixing over the region would fall by 12% by 2050 and
a remarkable 44% by 2100. This dramatically increased stratification
would, at first, result in very large blooms of phytoplankton as the
surface waters see far more oxygen and the depths become ever-more
deprived. This riot of microbial life may seem a positive development
for the Ross Sea. But, if anything, it is a sign of oceanic
productive zones moving southward to the polar region.
More
ominous is the impact on krill and larger animals dependent on these
small swimmers. Sea ice is critical to the survival of many krill
species. And with its decline, these marine animals are likely to be
negatively impacted.
According
to lead author, Dr. Walker Smith:
our results suggest that phytoplankton production will increase and become more diatomaceous. Other components of the Ross Sea food web will likely be severely disrupted, creating significant but unpredictable impacts on the ocean’s most pristine ecosystem.
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