[Paleopsych] SW: On the Beginning of the Last Ice Age

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Date: Tue, 24 May 2005 13:53:30 -0400 (EDT)
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Subject: SW: On the Beginning of the Last Ice Age

Paleoclimate: On the Beginning of the Last Ice Age

    The following points are made by Kurt M. Cuffey (Nature 2004 431:133):
    1) The relatively warm and stable climate that humanity has enjoyed
    for the past 10,000 years will inevitably give way to a new ice age --
    a tremendous environmental transformation that is destined to bury the
    sites of Boston, Edinburgh and Stockholm under glacial ice. In The Day
    After Tomorrow, the Hollywood movie most notable for its public abuse
    of thermodynamics, a new ice age starts in only one week. What does
    such a transition look like in reality?
    2) A new ice core(1) that samples the entire 3-km thickness of the
    north-central Greenland ice sheet provides us with an unprecedentedly
    rich and precise view of the onset of the most recent ice age, some
    120,000 years ago. And it is from the location of greatest interest --
    the North Atlantic region, where rapid climate changes have been most
    dramatic in the past. This achievement is the result of the efforts of
    the multinational North Greenland Ice Core Project (NGRIP). Individual
    years of snow deposition are distinguishable for events as far back as
    123,000 years in the past. A few years ago, such a resolution was
    thought to be unattainable.
    3) The story of how the impossible became possible would itself make a
    fine movie, complete with dramatic scenes of enlightenment in the mass
    spectrometry lab as isotope analyses reveal past climatic changes. In
    the early 1990s, two deep ice cores recovered from central Greenland
    yielded a detailed environmental history extending 100,000 years back
    in time, through the entirety of the last glacial climate(2). These
    showed that climate was extremely unstable. Within the space of a few
    decades, the North Atlantic region could evidently warm by 10 C, while
    smaller changes of temperature and moisture occurred over wide areas
    of the planet(3).
    4) Unfortunately, structural disturbance of the deepest ices(4)
    prevented these cores from revealing either the onset of the glacial
    period or events during the preceding warm interglacial period, known
    as the "Eemian", about 130,000 to 120,000 years ago. Initial reports
    to the contrary(5), highlighting apparent climate instabilities within
    the Eemian, were clearly mistaken, as the new report demonstrates(1).
    Yet the degree of climate stability during the Eemian is of intense
    interest: the Eemian was slightly warmer than the world is now,
    providing an analogue for a possible future climate warmed by
    atmospheric pollution.
    References (abridged):
    1. North Greenland Ice Core Project members Nature 431, 147-151 (2004)
    2. Hammer, C., Mayewski, P. A., Peel, D. & Stuiver, M. (eds) J.
    Geophys. Res. 102 (C12), 26317-26886 (1997)
    3. Severinghaus, J. P. & Brook, E. J. Science 386, 930-934 (1999)
    4. Chappellaz, J., Brook, E., Blunier, T. & Malaize, B. J. Geophys.
    Res. 102, 26547-26557 (1997)
    5. Greenland Ice-Core Project members Nature 364, 203-208 (1993)
    Nature http://www.nature.com/nature
    Related Material:
    The following points are made by A.J. Weaver and C. Hillaire-Marcel
    (Science 2004 304:400):
    1) A popular idea in the media is that human-induced global warming
    will cause another ice age. But where did this idea come from? Several
    recent magazine articles (1-3) report that abrupt climate change was
    prevalent in the recent geological history of Earth and that there was
    some early (albeit controversial) evidence from the last interglacial
    -- thought to be slightly warmer than preindustrial times (4) -- that
    abrupt climate change was the norm (5). Consequently, the articles
    postulate a sequence of events that goes something like this: If
    global warming were to boost the hydrological cycle, enhanced
    freshwater discharge into the North Atlantic would shut down the AMO
    (Atlantic Meridional Overturning), the North Atlantic component of
    global ocean overturning circulation. This would result in downstream
    cooling over Europe, leading to the slow growth of glaciers and the
    onset of the next ice age.
    2) This view prevails in the popular press despite a relatively solid
    understanding of glacial inception and growth. What glacier formation
    and growth require is, of course, a change in seasonal incoming solar
    radiation (warmer winters and colder summers) associated with changes
    in Earth's axial tilt, its longitude of perihelion, and the precession
    of its elliptical orbit around the Sun. These small changes must then
    be amplified by feedback from reflected light associated with enhanced
    snow/ice cover, vegetation associated with the expansion of tundra,
    and greenhouse gases associated with the uptake (not release) of
    carbon dioxide and methane.
    3) Several modeling studies provide outputs to support this
    progression. These studies show that with elevated levels of carbon
    dioxide, such as those that exist today, no permanent snow can exist
    over land in August (as temperatures are too warm), a necessary
    prerequisite for the growth of glaciers in the Northern Hemisphere.
    These same models show that if the AMO were to be artificially shut
    down, there would be regions of substantial cooling in and around the
    North Atlantic. Berger and Loutre (2002) specifically noted that "most
    CO2 scenarios led to an exceptionally long interglacial from 5000
    years before the present to 50,000 years from now ... with the next
    glacial maximum in 100,000 years. Only for CO2 concentrations less
    than 220 ppmv was an early entrance into glaciation simulated." They
    further argued that the next glaciation would be unlikely to occur for
    another 50,000 years.
    4) Although most paleoclimatologists would agree that the past is
    unlikely to provide true analogs of the future, past climate synopses
    are valuable for confronting the results of modeling experiments or
    for illustrating global warming. A reduction of the AMO due to a
    global warming-induced increase in freshwater supplies to the North
    Atlantic is often discussed in relation to a short event that occurred
    some 8200 years ago (8.2 ka). During this event, one of the largest
    glacial lakes of the Laurentide Ice Sheet, Lake Ojibway, drained into
    the North Atlantic through Hudson Strait, quickly releasing enormous
    quantities of fresh water. However, unequivocal evidence that this
    event resulted in a substantial reduction of the AMO has apparently
    not yet been obtained.
    References (abridged):
    1. S. Rahmstorf, New Scientist 153, 26 (8 February 1997)
    2. W. H. Calvin, Atlantic Monthly 281, 47 (January 1998)
    3. B. Lemley, Discover 23, 35 (September 2002)
    4. IPCC, Climate Change 2001, The Scientific Basis. Contribution of
    Working Group I to the Third Scientific Assessment Report of the
    Intergovernmental Panel on Climate Change, J. T. Houghton et al., Eds.
    (Cambridge Univ. Press, Cambridge, 2001)
    5. GRIP Project Members, Nature 364, 203 (1993)
    Science http://www.sciencemag.org
    Related Material:
    The following points are made by Karl Sabbagh (citation below):
    1) Over millennia, the world has experienced a series of ice ages,
    periods when large areas of the surface were covered with a sheet of
    ice thousands of meters deep. The most widely accepted theory for the
    cause of the ice ages is based on the fact that there have been
    changes over millions of years in the tilt of the Earth's axis and in
    the circularity of its orbit. Those changes have been cyclical and led
    to long periods when some parts of the Earth's surface received less
    light and heat from the Sun.
    2) Scientists recognize five major ice ages, the first about 2 billion
    years ago, then three more about 600 million, 400 million, and 300
    million years ago, and the last beginning 1.7 million years ago and
    finishing only about 10,000 years ago. The last, the Quaternary Ice
    Age, was a period when the diversity of life-forms on land not covered
    by ice was greater than it had been during the previous ice ages and
    during which there were major effects on plants and animals as the
    temperature dropped and ice sheets and glaciers formed from water that
    had evaporated from the sea. As the cold took its grip, not overnight
    but over thousands of years, the relationship between land and sea
    changed, caused partly by climate, partly by the weight of ice
    pressing down on the land.
    3) The process that froze water vapor into ice and deposited it on the
    land effectively depleted the sea of water that would otherwise
    condense into rain, run into rivers, and flow on to the sea. As more
    water froze and water continued to evaporate from the ocean, the sea
    level dropped, revealing areas that had been covered by water and
    expanding the total land area. For an area like the Hebrides, a series
    of separate islands before the Ice Age, this process would have turned
    them into much larger areas of land, possibly even into one
    interconnecting land mass.
    Adapted from: Karl Sabbagh: A Rum Affair: A True Story of Botanical
    Fraud. Da Capo Press, 2001, p.23. More information at:

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