How
Global Warming May Cause the Next Ice Age
by Thom Hartmann
OpEdNews.Com
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.
This
article was adapted from the new, updated edition of "The
Last Hours of Ancient Sunlight" by Thom Hartmann (thom
at thomhartmann.com), due out from Random House/Three Rivers
Press in March. www.thomhartmann.com
