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					A Melting Planet
                   Major Points
   Glacier formation and dynamics
   Glacier distribution
   Retreat of mountain glaciers
   Ice sheets of Antarctica and Greenland
   Effects of ice loss
                  Glacier Formation
   A glacier must form under three conditions: the regional climate must
    be cold enough that snow will not melt away entirely during the
    summer, there must be sufficient snowfall for accumulation to occur,
    and the slope must be gradual enough so that the snow pack does not
    slide away.
   As snowfall accumulates in the zone of accumulation, it exerts pressure
    on the snow beneath it. Over time, this pressure becomes strong
    enough that the underlying layers of snow turn to glacial ice called firn.
   Gravity will pull the ice to lower altitudes, which, in warmer regions,
    will cause the toe of the glacier to cross the equilibrium line into the
    zone of ablation, where sublimation (the evaporation of ice into water
    vapor) causes glacial mass to be lost.
Glacier Dynamics
                 Glacial Dynamics
   If the rate at which snow accumulates in the zone of
    accumulation exceeds the rate of sublimation in the zone of
    ablation, then the toe of the glacier will move forward into
    previously unglaciated terrain. This is referred to as glacial
    advance.
   Conversely, if the rate of sublimation in the zone of ablation
    exceeds the rate of accumulation, then the toe of the glacier will
    move backward. This is called glaical retreat.
Advance and Retreat
                  Glacial Distribution
   The vast majority of ice on earth
    lies in the ice sheets of Antarctica
    (91.8%) and Greenland (7.9%).
    The remaining .3% is distributed
    in alpine and piedmont glaciers
    around the world.
   In terms of the area of ice
    coverage, the Antarctic ice sheets
    account for 85.7%, Greenland
    10.9%, and the rest of the world’s
    glaciers account for 3.4%. Of this
    3.4%, two-thirds are found in ice
    caps and ice fields, and one-third
    alpine glaciers.
Glacial Distribution
        Effects of Global Warming
   It is accepted that the earth is warming due to human activities
   Since many glaciers are in lower latitudes than the polar ice
    sheets, they are more susceptible to climate change.
   As the line of equilibrium rises in altitude due to warming
    temperatures, the zone of accumulation shrinks while the zone
    of ablation grows.
   In this way glaciers around the world are retreating.
             Glacier National Park
   Due to the park’s relatively low latitude and the low elevation of
    its glaciers, it especially susceptible to warming temperatures.
   Of the 83 observed glaciers in the park that are greater than 0.1
    sq km, 34 are named as well as three that are not the minimum
    area. All of these 37 glaciers have had considerable loss of mass
    and have retreated dramatically since the mid 1800’s.
   The reduction in area is between 46% and 77% on varying
    glaciers in the park.
   A recent computer model indicates that at present rates of
    warming all glaciers in the park will disappear by 2030.
Glacier Disappearance
                  Franz Josef Glacier
    The Franz Josef valley is steep, narrow, and long-characteristics that
    accentuate the glacier's very quick response to changing local conditions. Like
    other glaciers, Franz Josef's advance and retreat patterns reflect changes of
    precipitation delivery to its accumulation zone in relation to the temperatures
    within its ablation zone-it just reflects the relationship more quickly than
    other glaciers.

   According to New Zealand's National Institute of Water and Atmospheric
    Research (NIWA), a long lasting "shift" in New Zealand's climate started
    around 1977. This shift coincided with an eastward movement in the
    longitude of the South Pacific Convergence Zone, and more frequent El
    Nino events in the recent record.
               FJ Glacier Continued
   The shift meant more persistent westerlies over central New Zealand,
    resulting in the west of South Island becoming 10% wetter and 5% cloudier
    with more damaging floods.

   Since 1977 temperatures have continued to rise, resulting in warmer night
    time temperatures and fewer frosts nationwide, and an increase in very hot
    days in eastern areas in recent decades. The increase in precipitation in the
    west of South Island could explain Franz Josef's most recent advance and the
    reversal, along with the continuing increase in temperatures, may explain its
    current trend to retreat, which will dominate over the long term.

   As of May of 2002, "The 48 glaciers of the Southern Alps monitored annually
    by NIWA continue to lose ice mass...This is the fourth year in five in which
    the glaciers have lost ice mass, an ongoing trend which began in 1998. The
    loss over the past year was among the most pronounced recorded."
Franz Josef Glacier
FJ Glacier Movements
                         Ice Sheets
   The ice sheets of Antarctica and Greenland represent 97% of the
    world’s total glaciated area. They also contain 99.7% of all
    glaciated ice in the world. Recent analysis estimates that nearly
    80% of the world’s freshwater resides in these ice sheets.
   Unlike most alpine and piedmont glaciers, the ice sheets of
    Antarctica and Greenland are in a relatively stable climate. Even
    with a rise in global temperatures, the regional climate of the ice
    sheets would remain sufficiently cold.
   The Greenland ice sheet covers nearly 2 million square km., and
    is in a slightly warmer climate than the Antarctic sheet due to its
    lower latitude.
                              Antarctica
   Antarctica is composed of two major, geologically distinct parts bridged by a
    vast ice sheet.
   East Antarctica, the larger of the two, is roughly the size of the United States
    and is composed of continental crust covered by an ice sheet that averages 1.6
    miles in thickness.
   West Antarctica, the smaller portion, is comprised of small blocks of
    continental crust covered by the West Antarctic Ice Sheet and an Andean-like
    mountain chain forming the Antarctic Peninsula. Most of the West Antarctic
    Ice Sheet is grounded below sea level, in places over 1.5 miles below sea level.
   These two ice sheets cover all but 2% of Antarctica's 14 million square
    kilometers. At its thickest point the ice sheet is almost 14,000 feet deep.
                Effects of Ice Loss
   Increased glacial melt could cause increased flooding on a
    regional scale.
   Regions which rely on melt water from glaciers for irrigation or
    hydroelectric power could face water shortages in the future
    when glaciers shrink.
   Loss of glaciers in national parks could result in a decrease in
    tourism to areas that rely on tourism for their economy.
   Unforeseen effects of a decrease of ocean salinity.
   Change in sea level…
                   Sea Level Change
   The average rate of sea level rise in the past century was between .3mm/yr
    and 3mm/yr. This corresponds with the rise in global temperatures.
   With an expected rise in temperatures between 1.5 and 4.5 degrees C over the
    next century, sea level is also expected to rise.
   There are three main factors that contribute to the change in sea level:
    thermal expansion, ice sheet mass change, and glacier mass change.
   Thermal expansion is the increase of the volume of water as the temperature
    rises, and it can have a significant effect on sea level change.
   It is estimated that thermal expansion alone contributed between 3-6cm over
    the past century. Future projections estimate that at current warming rates
    thermal expansion alone could contribute .1-.5mm/yr to future sea levels.
             Ice Sheet Mass Change
   Due to the relative stability of the polar climates, the polar ice sheets have not
    contributed much to the rise in sea level.
   It is expected that as global temperatures increase, precipitation rates around
    the world will also increase, including in the dry polar regions.
   The increased accumulation rate will outweigh any increase of sublimation
    caused by increased temperatures for the Antarctic ice sheet. This will result
    in a decrease in sea level by .5 mm/yr per degree C from the Antarctic sheet.
    However the stability of the West Antarctic ice sheet is uncertain.
   Greenland, however, will be slightly more affected by an increase in
    temperatures due to its low latitude, so it is estimated to add .5 mm/yr per
    degree C. Therefore the polar ice sheets actually cancel each other out.
            West Antarctic Ice Sheet
   The West Antarctic Ice Sheet, containing more than 3 million cubic
    kilometers of ice, is the last ice sheet on Earth resting in a deep marine basin
    and is the most likely player in any future, rapid sea level rise.
   It is comprised of a grounded ice sheet, a marine ice sheet (grounded below
    sea-level) and an extensive floating ice shelf.
   Glacial geologic studies have shown that this type of ice sheet is inherently
    unstable and vulnerable to rapid collapse. Nearly 90% of the ice flowing
    across West Antarctica converges into ice streams that are the most dynamic
    and unstable components of the ice sheet.
   Some of these ice streams may be responding to climatic and sea-level
    changes of the recent past, which could lead to more rapid retreat and global
    sea-level rise in the future. A few active volcanoes may also affect the ice
    sheet's behavior.
   The sea level equivalent of the WAIS is about 5 m.
                Glacier Mass Change
   Mountain glaciers, although small in volume, are much more affected by
    warming temperatures, so their impact on the future sea levels is significant. It
    is estimated that glaciers accounted for 4 cm of sea level rise in the past
    century.
   If all the glaciers in the world melted, it would result in a .5 m rise in sea level.
    If the polar ice sheets melted it would result in a 70 m rise in sea level,
    however this is impossible within the foreseeable future, whereas it is possible
    for most of the world’s glaciers to melt.
   At a 4 degrees C increase in global temperature over the next century, it is
    estimated that glaciers would contribute 20 cm to sea level rise.
                         Summary
   The increase in global temperatures is resulting in a rapid
    decrease of the volume of mountain glaciers around the world,
    and an increase in sea level.
   The East Antarctic ice sheet is actually growing due to increased
    precipitation rates, thereby reducing sea-level.
   The West Antarctic ice sheet is increasing in volume, but it is
    also becoming less stable and could partially collapse in the
    distant future.
   The Greenland ice sheet is becoming more sensitive to the
    changing climate, but is considerably less affected than mountain
    glaciers.

				
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posted:8/31/2012
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