Transcript Glaciers (PartI) - University of Colorado Boulder

GLACIERS AND CLIMATE
• Mass balance
• ELA
• Pleistocene
glaciation
• Milankovic cycle
• Albedo feedbacks
Quelcaya ice cap, Peru
Geographical and Climatic
conditions
• high snowfall in winter
• cool temperatures in summer
• Moisture important!!!
– Eg: Siberia and parts of Antarctica: low temperatures
meet glacier growth requirements, but
lack of adequate precipitation prevents glacier
development
Annual Glacier Mass Balance
• (Net)Accumulation zone = area where ice
accumulates
• (Net) Ablation zone= area where glacial ice
melts
• Equilibrium line
where accumulation=ablation
balance = 0 (at equilibrium)
Equilibrium Line Altitude
Where is the ELA?
Mass balance
• NEGATIVE: glacier gets smaller
• POSITIVE: glacier gets larger
• ZERO MASS BALANCE:
– no change in glacier size (mass,volume)
– GLACIER STILL MOVING FORWARD!!!
ELA and climate
• Positive Mass Balance -- ELA lower
– Glacier gets larger
• Negative Mass Balance -- ELA higher
– Glacier gets smaller
How do glaciers reflect climate
change?
• Climate change:
– changes in temperature
– changes in amount of moisture
– Glaciers sensitive to temperature fluctuations
• climate change can cause glaciers to melt
• but the relationship is not straightforward,
– eg. Antarctica:climate change-->warmer-->more
evaporation from ocean ->more water vapor ->
more snowfall!
Ice ages
• Ice ages return every 100,000 years
• approx. 20 ice ages
• Pleistocene = most recent ice age, that
started about 2 million years ago and ended
~10,000 yrs ago
• 4 major advances of ice, most recent ones:
– Laurentide: ended 20,000 yrs ago
– Wisconsin: ended 100,000 yrs ago
– Presently we are in an interglacial period
Causes of ice ages?
Milankovic cycles
long term variations in Earth’s orbit around the Sun:
Glacial ages
• During the last Ice Age, glaciers covered
32% of the total land area.
• Little Ice Age:
– 17th century - late 19th century
– consistently cool temperatures
– significant glacier advances.
Earth’s climate record
Glaciers sensitive to climate
changes: a few facts
• strong warming over the last 50-200 yrs
• increasing CO2 levels
• Alpine glaciers have been experiencing
rapid retreat
• Ice cap on Mt. Kilimanjaro has been
decreasing by 82% in the last 88 years
• Glaciers in the Alps decreased by 50% in
volume
Ice-albedo (positive) feedback
Global warming
+
+
Glacial melt
More energy
absorbed
+
Decrease in surface
of ice
+
Decrease in albedo
+
Climatic responses- scenarios
• winter temperature:
– less, not more, snow
– polar areas get little precip. (cold air)
– if summer ablation same -- glacier retreats
• summer temperature:
– more cloud cover
– less summer ablation
– if winter accumulation same -- glacier grows
Climatic response (cont’d)
• winter precipitation (snowfall)
– if no change in temperature
– some snow survives over summer
– glacier advances
– temperature crucial factor-
Glacier response -summary
• Alpine glaciers and N.Hem. Ice caps
expected to retreat under global warming
scenario
• NOTE: Antarctica expected to grow due to
possible increase in humidity
Aster image, Patagonia, Chile
Indian Himalayas:
Glacier ablation at
Gangotri, source of
the holy Ganges
• glacier terminus retreated by
3km
ASTER Image courtesy of: NASA EROS
Data Center, Sept. 9, 2001
Summary: GLACIERS AND
CLIMATE
• Mass balance
• ELA
• Pleistocene
glaciation
• Milankovic cycle
• Albedo feedbacks
Quelcaya ice cap, Peru