Thom Hartman/www.commondreams.org: And when might that
threshold be reached? Nobody knows - the action of the
Great Conveyor Belt in defining ice ages was
discovered only in the last decade. Preliminary
computer models and scientists willing to speculate
suggest the switch could flip as early as next year,
or it may be generations from now. It may be wobbling
right now, producing the extremes of weather we've
seen in the past few years.
Remember, you can use the LNS's searchable database to
find some other important news stories on global
warming...
Save the Environment, Show Up for Democracy in 2004:
Defeat Bush (again!)
http://truthout.org/docs_04/020104G.shtml
How Global Warming May Cause the Next Ice Age...
By Thom Hartmann
Commondreams.org
Friday 30 January 2004
While global warming is being officially ignored
by the political arm of the Bush administration, and
Al Gore's recent conference on the topic during one of
the coldest days of recent years provided joke fodder
for conservative talk show hosts, the citizens of
Europe and the Pentagon are taking a new look at the
greatest danger such climate change could produce for
the northern hemisphere - a sudden shift into a new
ice age. What they're finding is not at all
comforting.
In quick summary, if enough cold, fresh water
coming from the melting polar ice caps and the melting
glaciers of Greenland flows into the northern
Atlantic, it will shut down the Gulf Stream, which
keeps Europe and northeastern North America warm. The
worst-case scenario would be a full-blown return of
the last ice age - in a period as short as 2 to 3
years from its onset - and the mid-case scenario would
be a period like the "little ice age" of a few
centuries ago that disrupted worldwide weather
patterns leading to extremely harsh winters, droughts,
worldwide desertification, crop failures, and wars
around the world.
Here's how it works.
If you look at a globe, you'll see that the
latitude of much of Europe and Scandinavia is the same
as that of Alaska and permafrost-locked parts of
northern Canada and central Siberia. Yet Europe has a
climate more similar to that of the United States than
northern Canada or Siberia. Why?
It turns out that our warmth is the result of
ocean currents that bring warm surface water up from
the equator into northern regions that would otherwise
be so cold that even in summer they'd be covered with
ice. The current of greatest concern is often referred
to as "The Great Conveyor Belt," which includes what
we call the Gulf Stream.
The Great Conveyor Belt, while shaped by the
Coriolis effect of the Earth's rotation, is mostly
driven by the greater force created by differences in
water temperatures and salinity. The North Atlantic
Ocean is saltier and colder than the Pacific, the
result of it being so much smaller and locked into
place by the Northern and Southern American
Hemispheres on the west and Europe and Africa on the
east.
As a result, the warm water of the Great Conveyor
Belt evaporates out of the North Atlantic leaving
behind saltier waters, and the cold continental winds
off the northern parts of North America cool the
waters. Salty, cool waters settle to the bottom of the
sea, most at a point a few hundred kilometers south of
the southern tip of Greenland, producing a whirlpool
of falling water that's 5 to 10 miles across. While
the whirlpool rarely breaks the surface, during
certain times of year it does produce an indentation
and current in the ocean that can tilt ships and be
seen from space (and may be what we see on the maps of
ancient mariners).
This falling column of cold, salt-laden water
pours itself to the bottom of the Atlantic, where it
forms an undersea river forty times larger than all
the rivers on land combined, flowing south down to and
around the southern tip of Africa, where it finally
reaches the Pacific. Amazingly, the water is so deep
and so dense (because of its cold and salinity) that
it often doesn't surface in the Pacific for as much as
a thousand years after it first sank in the North
Atlantic off the coast of Greenland.
The out-flowing undersea river of cold, salty
water makes the level of the Atlantic slightly lower
than that of the Pacific, drawing in a strong surface
current of warm, fresher water from the Pacific to
replace the outflow of the undersea river. This
warmer, fresher water slides up through the South
Atlantic, loops around North America where it's known
as the Gulf Stream, and ends up off the coast of
Europe. By the time it arrives near Greenland, it's
cooled off and evaporated enough water to become cold
and salty and sink to the ocean floor, providing a
continuous feed for that deep-sea river flowing to the
Pacific.
These two flows - warm, fresher water in from the
Pacific, which then grows salty and cools and sinks to
form an exiting deep sea river - are known as the
Great Conveyor Belt.
Amazingly, the Great Conveyor Belt is only thing
between comfortable summers and a permanent ice age
for Europe and the eastern coast of North America.
Much of this science was unknown as recently as
twenty years ago. Then an international group of
scientists went to Greenland and used newly developed
drilling and sensing equipment to drill into some of
the world's most ancient accessible glaciers. Their
instruments were so sensitive that when they analyzed
the ice core samples they brought up, they were able
to look at individual years of snow. The results were
shocking.
Prior to the last decades, it was thought that
the periods between glaciations and warmer times in
North America, Europe, and North Asia were gradual. We
knew from the fossil record that the Great Ice Age
period began a few million years ago, and during those
years there were times where for hundreds or thousands
of years North America, Europe, and Siberia were
covered with thick sheets of ice year-round. In
between these icy times, there were periods when the
glaciers thawed, bare land was exposed, forests grew,
and land animals (including early humans) moved into
these northern regions.
Most scientists figured the transition time from
icy to warm was gradual, lasting dozens to hundreds of
years, and nobody was sure exactly what had caused it.
(Variations in solar radiation were suspected, as were
volcanic activity, along with early theories about the
Great Conveyor Belt, which, until recently, was a
poorly understood phenomenon.)
Looking at the ice cores, however, scientists
were shocked to discover that the transitions from ice
age-like weather to contemporary-type weather usually
took only two or three years. Something was flipping
the weather of the planet back and forth with a
rapidity that was startling.
It turns out that the ice age versus temperate
weather patterns weren't part of a smooth and linear
process, like a dimmer slider for an overhead light
bulb. They are part of a delicately balanced
teeter-totter, which can exist in one state or the
other, but transits through the middle stage almost
overnight. They more resemble a light switch, which is
off as you gradually and slowly lift it, until it hits
a mid-point threshold or "breakover point" where
suddenly the state is flipped from off to on and the
light comes on.
It appears that small (less that .1 percent)
variations in solar energy happen in roughly 1500-year
cycles. This cycle, for example, is what brought us
the "Little Ice Age" that started around the year 1400
and dramatically cooled North America and Europe
(we're now in the warming phase, recovering from
that). When the ice in the Arctic Ocean is frozen
solid and locked up, and the glaciers on Greenland are
relatively stable, this variation warms and cools the
Earth in a very small way, but doesn't affect the
operation of the Great Conveyor Belt that brings
moderating warm water into the North Atlantic.
In millennia past, however, before the Arctic
totally froze and locked up, and before some critical
threshold amount of fresh water was locked up in the
Greenland and other glaciers, these 1500-year
variations in solar energy didn't just slightly warm
up or cool down the weather for the landmasses
bracketing the North Atlantic. They flipped on and off
periods of total glaciation and periods of temperate
weather.
And these changes came suddenly.
For early humans living in Europe 30,000 years
ago - when the cave paintings in France were produced
- the weather would be pretty much like it is today
for well over a thousand years, giving people a chance
to build culture to the point where they could produce
art and reach across large territories.
And then a particularly hard winter would hit.
The spring would come late, and summer would
never seem to really arrive, with the winter snows
appearing as early as September. The next winter would
be brutally cold, and the next spring didn't happen at
all, with above-freezing temperatures only being
reached for a few days during August and the snow
never completely melting. After that, the summer never
returned: for 1500 years the snow simply accumulated
and accumulated, deeper and deeper, as the continent
came to be covered with glaciers and humans either
fled or died out. (Neanderthals, who dominated Europe
until the end of these cycles, appear to have been
better adapted to cold weather than Homo sapiens.)
What brought on this sudden "disappearance of
summer" period was that the warm-water currents of the
Great Conveyor Belt had shut down. Once the Gulf
Stream was no longer flowing, it only took a year or
three for the last of the residual heat held in the
North Atlantic Ocean to dissipate into the air over
Europe, and then there was no more warmth to moderate
the northern latitudes. When the summer stopped in the
north, the rains stopped around the equator: At the
same time Europe was plunged into an Ice Age, the
Middle East and Africa were ravaged by drought and
wind-driven firestorms. .
If the Great Conveyor Belt, which includes the
Gulf Stream, were to stop flowing today, the result
would be sudden and dramatic. Winter would set in for
the eastern half of North America and all of Europe
and Siberia, and never go away. Within three years,
those regions would become uninhabitable and nearly
two billion humans would starve, freeze to death, or
have to relocate. Civilization as we know it probably
couldn't withstand the impact of such a crushing blow.
And, incredibly, the Great Conveyor Belt has
hesitated a few times in the past decade. As William
H. Calvin points out in one of the best books
available on this topic ("A Brain For All Seasons:
human evolution & abrupt climate change"): ".the
abrupt cooling in the last warm period shows that a
flip can occur in situations much like the present
one. What could possibly halt the salt-conveyor belt
that brings tropical heat so much farther north and
limits the formation of ice sheets? Oceanographers are
busy studying present-day failures of annual flushing,
which give some perspective on the catastrophic
failures of the past. "In the Labrador Sea, flushing
failed during the 1970s, was strong again by 1990, and
is now declining. In the Greenland Sea over the 1980s
salt sinking declined by 80 percent. Obviously, local
failures can occur without catastrophe - it's a
question of how often and how widespread the failures
are - but the present state of decline is not very
reassuring."
Most scientists involved in research on this
topic agree that the culprit is global warming,
melting the icebergs on Greenland and the Arctic
icepack and thus flushing cold, fresh water down into
the Greenland Sea from the north. When a critical
threshold is reached, the climate will suddenly switch
to an ice age that could last minimally 700 or so
years, and maximally over 100,000 years.
And when might that threshold be reached? Nobody
knows - the action of the Great Conveyor Belt in
defining ice ages was discovered only in the last
decade. Preliminary computer models and scientists
willing to speculate suggest the switch could flip as
early as next year, or it may be generations from now.
It may be wobbling right now, producing the extremes
of weather we've seen in the past few years.
What's almost certain is that if nothing is done
about global warming, it will happen sooner rather
than later.