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  • Pat N self only
    ... November 23, 1999 Lessons From Ancient Heat Surge By WILLIAM K. STEVENS What happens when great
    Message 1 of 1 , Nov 4, 2005
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      ---------- Forwarded Message ----------
      November 23, 1999
      <http://www.treepower.org/news/nytglobalwarming3.html>
      Lessons From Ancient Heat Surge

      By WILLIAM K. STEVENS

      What happens when great amounts of heat-trapping greenhouse gases are
      injected into the atmosphere in a relatively short span of earth
      history, as is happening today as a result of the burning of coal,
      oil and natural gas?

      One way to help answer this urgent climatic question of the day is to
      examine what has happened in similar situations in the remote past.
      Now, American and Australian scientists are reporting evidence that
      the biggest global warming in the last 100 million years may have
      been touched off by a sudden blowout of greenhouse gases from the
      ocean floor.

      The scientists say that for a relatively brief period around 55
      million years ago, after the extinction of the dinosaurs but long
      before the onset of today's pattern of periodic ice ages, the
      temperature of the earth's surface in northern latitudes, and of the
      deep ocean, soared by some 9 to 12 degrees Fahrenheit.

      This is substantially more than the 5 to 9 degrees the world has
      warmed since the depths of the last ice age 18,000 to 20,000 years
      ago.

      So great was the effect of the warming, experts say, that it wiped
      out many species of marine life and created climatic conditions that
      led to an explosive expansion in the number and variety of mammal
      species. It was at this time that the primates, from which Homo
      sapiens eventually evolved, first appeared.

      The analogy to today's conditions is far from perfect, and many
      questions remain to be answered, but those who have investigated the
      ancient warming spike say it reinforces a belief that has lately been
      growing among climate scientists: that a gradual warming of the
      climate can abruptly soar to new heights once a certain threshold is
      reached.

      That is what scientists believe happened in the case of the warming
      55 million years ago -- and perhaps what could happen again, in
      certain conditions.

      The chief greenhouse gas was and is carbon dioxide, and since the
      start of the Industrial Revolution in the 18th century, its
      atmospheric concentration has gradually increased by nearly 30
      percent. The average global surface temperature has risen by about 1
      degree or a little more in the last century.

      Mainstream scientists believe, based on computerized simulations of
      the climate's workings, that the temperature will rise by about
      another 3.5 degrees by the year 2100 if greenhouse gas emissions
      continue at the present rate.

      A gradual warming of unknown cause preceded the sharp upward spike in
      temperature 55 million years ago, said Miriam E. Katz, a
      paleooceanographer at Rutgers University, who is the leading author
      of a report on the ancient phenomenon in the current issue of the
      journal Science.

      But at some point, the warming crossed a threshold that abruptly
      kicked the temperature up to a new level, said another author of the
      Science paper, Dr. Gerald R. Dickens of James Cook University in
      Australia. He compared it to the stretching of a rubber band: "You
      gradually pull at both ends and, at some instant, the rubber band
      suddenly breaks."

      What caused the climate to snap and send the temperature soaring,
      according to a hypothesis formulated by Dr. Dickens, was a sudden
      release of methane locked in the ocean floor, touched off by the
      previous, more gradual warming.

      Methane is a greenhouse gas in its own right, and when released from
      ocean sediments it also combines with oxygen to form carbon dioxide
      that eventually percolates to the atmosphere.

      Dr. Dorothy K. Pak of the University of California at Santa Barbara
      and Dr. Kenneth G. Miller of Rutgers are the other authors of the
      report in Science, which describes chemical and geological evidence
      of the ancient rush of greenhouse gases and the way it happened. The
      evidence was contained in corings and ultrasound readings of
      sediments on a subsea promontory called the Blake Nose, northeast of
      Cape Canaveral, Fla.

      The researchers believe that the original, gradual warming, beginning
      about 60 million years ago, caused a change in ocean circulation
      currents that pushed warm surface waters down into the deep sea.

      This deep-sea warming converted icelike solid methane locked in
      crystalline structures in the sea-floor sediments into gaseous form.

      This gas then blasted upward through the sediment, starting mudslides
      that freed the methane and allowed it to escape into the water and
      eventually to the atmosphere. On the way, it reacted with oxygen to
      produce globe-warming carbon dioxide.
      One effect of the warming spike, Ms. Katz says, was to transform the
      environment of the deep ocean, as evidenced by the extinction of more
      than half of all species of microscopic bottom-dwelling animals.

      The warming is also believed to have enabled that era's relatively
      small array of mammals to spread out into formerly frozen regions to
      colonize other continents, where they proliferated in many
      evolutionary directions.

      Among these were the ancestors of horses, apes and humans.

      Dr. Dickens has calculated that the sudden influx of carbon
      associated with the sharp spike of global warming 55 million years
      ago amounted to at least a billion billion metric tons.

      At present rates of carbon-dioxide emission from global sources,
      about two-thirds of that amount would be added to the atmosphere by
      2100.

      Some scientists say it is possible that before then, some threshold
      could again be surpassed, resulting in an abrupt but unknown change
      in climate.

      Many questions remain. The cause of the gradual warming that preceded
      the spike 55 million years ago is unknown.

      Nor do scientists know the magnitude of the atmospheric
      concentrations before the gradual warming trend and the spike,
      frustrating comparisons with today. Moreover, it is not clear how
      much of the ancient warming resulted from the influx of greenhouse
      gas and how much from accompanying changes in ocean circulation; Dr.
      Dickens believes both were involved.
      A further complication, says Dr. Dickens, is that the influx of
      greenhouse gases was spewed initially into the ocean 55 million years
      ago, but is going directly into the atmosphere today.

      That difference could affect the rate of the consequent warming,
      since the ocean's inertia might slow the migration of carbon dioxide
      into the air, making the ancient warming spike less abrupt than
      otherwise.

      The evidence drawn from ocean sediments in the new study was not
      fine-grained enough to determine just how sharp the ancient warming
      was, Dr. Pak said, though it took place within a few thousand years
      at most.

      Other large, abrupt climatic changes of the more recent past --
      during the transition out of the last ice age, for example -- have
      taken place within a human lifetime or less and sometimes within a
      decade, according to recent evidence.

      All of these complications muddy the possible comparison between what
      happened in the transformational climatic event 55 million years ago
      and what is happening today. Nevertheless, says Dr. Dickens, the
      ancient transformation provides a new and continuing opportunity to
      explore the possible effects of growing concentrations of greenhouse
      gases without resorting to computer-assisted simulations of the
      climate.

      And, he says, it teaches that "the earth can, for natural reasons,
      suddenly change dramatically."

      Posted by Tim
      AustinTex
      --
      <http://www.groundtruthinvestigations.com/>







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