A Melting Planet

1
A Melting Planet
2
Major Points

• Glacier formation and dynamics
• Glacier distribution
• Retreat of mountain glaciers
• Ice sheets of Antarctica and Greenland
• Effects of ice loss

3
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.

4
Glacier Dynamics
5
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.

6
Advance and Retreat
7
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 worlds glaciers
  account for 3.4. Of this 3.4, two-thirds are
  found in ice caps and ice fields, and one-third
  alpine glaciers.

8
Glacial Distribution
9
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.

10
Glacier National Park

• Due to the parks 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
  1800s.
• 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.

11
Glacier Disappearance
12
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.

13
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."

14
Franz Josef Glacier
15
FJ Glacier Movements
16
Ice Sheets

• The ice sheets of Antarctica and Greenland
  represent 97 of the worlds total glaciated
  area. They also contain 99.7 of all glaciated
  ice in the world. Recent analysis estimates that
  nearly 80 of the worlds 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.

17
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.

18
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

19
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.

20
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.

21
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.

22
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 worlds 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.

23
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.