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The
Ice Age Cometh
By Thom Hartmann
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 temperature 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 has 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 the 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 20 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 it 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 would 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.
This article was adapted from the new, updated edition of The Last
Hours of Ancient Sunlight by Thom Hartmann, due out from Random House/Three
Rivers Press in March.
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