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How Global  Warming May Cause the Next Ice Age
by Thom  Hartmann


Thom Hartmann will be a keynote  speaker at the Futurehealth Winter Brain, Optimal Functioning and  Positive Psychology and StoryCon Meeting   Feb 6-10, and will be broadcasting his nationally syndicated radio  show from the meeting on Feb 6, 9 and 10th.  Tapes of talks will be available.

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, due out from Random House/Three Rivers Press in March.
For updates and info, contact scott at planttrees dot org.