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Global warming 55 million years ago shifted ocean currents

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  • Greg Cannon
    http://www.breitbart.com/news/2006/01/04/060104185028.juffd4y7.html Global warming 55 million years ago shifted ocean currents Jan 04 1:50 PM US/Eastern An
    Message 1 of 1 , Jan 4, 2006

      Global warming 55 million years ago shifted ocean
      Jan 04 1:50 PM US/Eastern

      An extraordinary burst of global warming that occurred
      around 55 million years ago dramatically reversed
      Earth's pattern of ocean currents, a finding that
      strengthens modern-day concern about climate change, a
      study says.

      The big event, the Palaeocene/Eocene Thermal Maximum
      (PETM), saw the planet's surface temperature rise by
      between five and eight degrees C (nine and 16.2 F) in
      a very short time, unleashing climate shifts that
      endured tens of thousands of years.

      Scientists Flavia Nunes and Richard Norris of the
      Scripps Institution of Oceanography in California
      explored how these warmer temperatures might have
      affected ocean currents.

      They measured carbon-13 isotopes from 14 cores that
      had been drilled into the deep floor in four different
      ocean basins, taking samples from sediment layers
      deposited before, during and after the PETM.

      These isotopes are considered to be an indicator of
      the nutrients deposited by the water at the time. The
      higher the isotope value, the likelier that the source
      came from the deep ocean, the prime source for

      With a painstaking reconstruction, Nunes and Norris
      found that the world's ocean current system did a
      U-turn during the PETM -- and then, ultimately,
      reversed itself.

      Before the PETM, deep water upwelled in the southern
      hemisphere; over about 40,000 years, the source of
      this upwelling shifted to the northern hemisphere; it
      took another 100,000 years before recovering

      What unleashed the PETM is unclear. Most fingers of
      blame point to volcanic eruptions that disgorged
      gigatonnes of carbon dioxide, or coastal reservoirs of
      methane gas, sealed by icy soil, that were breached by
      warmer temperatures or receding seas.

      The huge temperature rise may have occurred within
      just few thousand years, but as Nunes and Norris point
      out, the effects were enduring and the lesson for
      mankind today is clear.

      "Modern CO2 input to the biosphere from fossil fuel
      sources is approaching that estimated for the PETM,
      raising concerns about future climate and circulation
      change," they warn.

      "The PETM example shows that anthropogenic (man-made)
      forcing may have lasting effects not only in global
      climate but in deep-ocean circulation as well."

      The study, which appears on Thursday in the British
      journal Nature, comes on the heels of research
      published in November which suggests that global
      warming is slowing the Atlantic current that gives
      western Europe its mild climate.

      The suspected reason for this is an inrush of
      freshwater into the northern Atlantic, caused by
      melting glaciers in Greenland and melting sea ice, and
      higher flow into the Arctic from Siberian rivers
      caused by greater rainfall.

      The influx brakes the conveyor belt in which warm
      surface water is taken up to the northeastern Atlantic
      from the tropics before returning down to the southern
      hemisphere as cool, deep-sea water.

      In 2001, the UN's top scientific authority on global
      warming, the Intergovernmental Panel on Climate Change
      (IPCC), estimated that there would be a temperature
      rise of 1.4 to 5.8 C (2.5 to 10.4 F) from 1990-2100.

      The increase was predicted according to scenarios of
      atmospheric carbon dioxide (CO2), ranging from 540 to
      970 parts per million (ppm).

      That compares with 280ppm for pre-industrial times and
      around 380ppm today, which is already the highest
      concentration of CO2 for 650,000 years.

      The higher the level, the greater the risk that a
      vicious circle of global warming could be unleashed,
      inflicting potentially irreversible damage to Earth's
      climate system, scientists say.
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