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How Global Warming May Cause the Next Ice Age...

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  • Julienne
    Published on Friday, January 30, 2004 by CommonDreams.org How Global Warming May Cause the Next Ice Age... by Thom Hartmann While global warming is being
    Message 1 of 1 , Jan 5, 2010
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      Published on Friday, January 30, 2004 by CommonDreams.org

      How Global Warming May Cause the Next Ice Age...

      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
      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

      Copyright 2004 by Thom Hartmann.

      http://www.commondreams.org/views04/0130-11.htm

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