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Transcript
Ice Ages and Climate Change
GLY 2010 – Summer 2014
Lecture 21
1
Discovery of an Ice Age
• Louis Agassiz, a SwissAmerican scientist and
physician, was the first to
recognize evidence for an ice
age
• Trained in medicine and
natural history, he was the first
to propose, in 1837, that earth
had been subjected to a past ice
age
• 1807 - 1873
2
Louis Agassiz
• Agassiz moved to the United States in 1846
• He became professor of zoology and geology
at Harvard University, and founded the
Museum of Comparative Zoology
• He became interested in the last glacial
advance in North America, and studied it for
the remainder of his life
3
Ice Ages
• Ice ages - are times when the entire Earth
experiences notably colder climatic
conditions
• During an ice age
 The polar regions are cold
 There are large differences in temperature
from the equator to the pole
 Large, continental-size glaciers or ice sheets
can cover enormous regions of the earth
4
Previous Ice Ages
• The climate history of earth is under active
investagation
• Two Precambrian ice ages are known
 2000 MYBP
 600 MYBP
 Late Paleozoic ice age, about 250 MYBP
 Pleistocene ice age
5
Late
Paleozoic
Glaciation
6
Plate Tectonics and Climate
• Glaciers can only form on land
• As plates move, evidence for a cold climate, in
the form of glaciation, can only exist when
land masses are present at high latitudes
• Movement of land masses also alters the
oceanic circulation pattern, a vital factor in
determining climate conditions
7
Pleistocene Glaciation
• Began about 1.6 MYBP
• There were at least 4 glacial advances
• Climate cooled 5-10ºC during glacial
episodes, warming in between
• Last episode peaked 18,000 years ago, ice
covering about 30% of the earth’s surface
8
North American Ice Cover
• Figure shows the
extent of ice
cover from
18,000 to 8000
years ago
• White is ice,
blue is glacial
meltwater lakes
9
Remnants of the
Ice
• Loess is very fine
sediment
• Extensive, thick loess
deposits generally
formed in areas
bordering large,
continental glaciers
• Loess is thickest just downwind of major river
valleys
10
U.S. Loess Deposits
11
Climate Questions
• What causes the onset of glacial conditions?
• What caused the alternation of glacial and
interglacial conditions during the Pleistocene?
12
Orbital Influence on Climate
• The earth’s orbit around the
sun, and rotation around its
own axis, influence climate
• Milutin Milankovitch
proposed on theory of
climate modification based
on variations in incoming
solar radiation, caused by
orbital variations
• 1879-1958
13
Variation in
Orbital
Eccentricity
• The shape of the orbit changes over a period of
about 100,000 years
• The change is exaggerated in the drawing for
14
clarity
Tilt of the
Rotation
Axis
• Varies over a 41,000 year period
• Varies from 21.5 to 24.5 degrees
15
Precession
of the Axis
• Earth’s axis wobbles, or precesses, over time,
like a spinning top
• This means the axis points to different places in
16
the sky over a 26,000 year period
Milankovitch Hypothesis
• Milankovitch combined these ideas in a
mathematical formulation that predicted their
combined effect on climate fluctuations of the
Pleistocene
• The three factors have almost no effect on the
total amount of solar energy reaching the earth
17
Orbital Variations and Climate Change
18
Effects of the
Milankovitch Hypothesis
• The effect of the various cycles is to change
the contrast between seasons
• Milder winters in high latitudes lead to climate
warming, and greater snowfall
• Cooler summers would reduce snowmelt
• Combined, this might trigger ice formation,
and lead to an ice age
• This can explain the alternating glacialinterglacial effects seen in the Pleistocene
19
Other Factors Effecting Climate
• Composition of the earth’s atmosphere
• Variations in reflectivity of the earth’s surface
20
Composition of the Earth’s
Atmosphere
• We know the present composition of the
atmosphere
• How can we measure it in the past?
 One method is to analyze gas bubbles trapped in
glacial ice at the time of formation
 Gas bubbles trapped in other substances, such as
amber, can also be analyzed
 Certain gases, such as carbon dioxide,
methane, and freon, are greenhouse gases
21
Greenhouse Effect
• Sun emits ultraviolet (UV - purple), visible
(green) and infrared (IR -red) wavelengths
• Earth emits ONLY emits IR energy
• CO2 traps IR, and greenhouse (earth) warms
22
Greenhouse
Gases
• Polyatomic gases with three of more atoms
may trap infrared radiation leaving the earth
• This radiation is earth’s cooling system
• The gases act like a blanket, warming earth
23
Global Warming
24
Measuring Temperature Over Time
• It is easy to measure current temperatures
• How do we measure temperatures at some
point in the past?
• We use geothermometers
 Most of these depend on the ratios of one isotope
to another
25
Oxygen Isotopes As
Geothermometers
• There are three stable isotopes of oxygen,
16O, 17O, and 18O
• 18O is heaviest, and moves the slowest, so
it is less like to be incorporated into oxygen
containing compounds, such as water (ice)
• As temperatures increase, the probability of
18O being incorporated increases
26
18O/16O
Fractionation
27
Oxygen
Geothermometer
Data
28
Ice Cores
• Ice cores in Greenland and at the Russian
Antarctic station (Vostok) have provided
radiometrically datable ice deposited more
than 420,000 years ago
• Oxygen isotope studies give us an essentially
continuous climate record for that period
29
Other Climate Indicators
• Calcite linings in underground channels
provide much longer climate records
• Calcite contains oxygen, so can be used as a
geothermometer
• Records may go back hundreds of
thousands of years
• Marine sediments have also been used for
geothermometry studies
30
Stalagmite Evidence
31
Temperatures at Glacial Maximum
Climate model
calculation
based on
several sources
of data
• Differences between the annual mean near-ground air
temperatures for present-day climate and for the climate
during the last ice age approximately 18,000 years ago 32
Cenozoic Climate
33
Glacial Pair Photography
• On the left is a photograph of Qori Kalis Glacier taken in July
1978, and on the right, a photograph taken from the same
vantage in July 2004
• Both photographs taken by Lonnie G. Thompson, Byrd Polar
Research Center, the Ohio State University
34
Muir Glacier
• On the left is a photograph of Muir Glacier taken on August
13, 1941, by glaciologist William O. Field; on the right, a
photograph taken from the same vantage on August 31, 2004,
by geologist Bruce F. Molnia of the United States Geological
Survey (USGS).
35
Sea-Level
Changes
• When temperature changes, sea-level rises or falls, due
to the melting of glaciers, and thermal expansion of seawater
• Since 1900, sea-level has risen ~ 20 centimeters, and is
estimated to rise as much as 100 centimeters by 2100 36
Post-Glacial Sea-Level Rise
37
Effect of Rising
Sea-level
• Uncontrolled, sea-level
rise by the year 2100
could lead to the
erosion or inundation of
38% to 61% of existing
coastal wetlands in the
United
States.
38
Sea-level Rise: Florida
39
North
America
if All Ice
Melted
40
Effects of Sea-Level Rise
•
•
•
•
•
Beach erosion
Salt water encroachment
Flooding of coastal areas
Changes to coastal wetlands
More information on climate change effects,
including sea-level rise, in the southeast is
available at:
http://www.epa.gov/climatechange/impactsadaptation/southeast.html
41
Bering Land
Bridge
• Increased glaciation results in lower sea-levels, and may
result in land bridge formation
• Ex - Bering Sea between Siberia and Alaska during
Wisconsin glaciation
• Humans, mastodons, and mammoths migrated from Asia
to N. America this way
• Camel and horse went the other way
42
Albedo
• Albedo is the reflectivity of the earth surface
• Ice reflects a lot of radiation
• Forests or sea-water are much darker, and
absorb more radiation
• Absorption leads to heating, and reflection to
cooling, of the earth’s atmosphere and surface
43
Effect of Albedo
• As ice melts, albedo decreases
• Ice has an albedo of about 0.7, which means
70 of the nergy hitting a surface is reflected to
space
• Ocean water has an albedo of 0.2
• Thus, as ice is converted to water, heating
increases
44
Effect of Meltwater on Glacier
45
Arctic Ice Melt
46
Arctic
Ice
Levels
• In June 2012, the Arctic lost a total of 2.86 million square kilometers (1.10
million square miles) of ice, the largest June ice loss in the satellite record.
• Ice level in June, 2012 in the Arctic was the second lowest since satellite
observations began in 1979 – this year isn’t far behind
47
Petermann
Glacier 2012
• The calving of a massive 46 square-mile iceberg two times the
size of Manhattan from Greenland's Petermann Glacier on July
14 - 18, 2012, as seen using MODIS satellite imagery
48
Petermann
Glacier - 2010
• The animation begins on August 5, 2010, and ends on
September 21, with images spaced about 8 days apart
• A 100 square-mile ice island broke off the Petermann Glacier
• It was the largest iceberg in the Arctic since 1962
49
Geogenic or Anthropogenic
Climate Change?
• Is climate change due to man or is it natural?
• Maps show predictions from climate models
50
Observed 1958-2008
• We are already seeing effects that resemble the models, which
increases confidence in the models
51
Current
Drought Map
• Severe to extreme drought
affected about 34 percent of
the contiguous United States
as of July 16, 2013, an
improvement of about 3
percent from last year at the
same time
• About 4.3 percent of the contiguous U.S. fell in the exceptional drought
category (D4)
52
Large Wildfires
• Large wildfires have been burning much larger areas
in recent years
• From 1884 to 1999 an average of 2.2 million acres burned
in the United States each year
• From 2000 to 2008 the average increased to 6.4 million
acres
• The figures are from a combined study by the Forest
Service and the USGS
53
Policy and Science
• The Senate Committee on Energy and Natural Resources
hearing on June 15, 2011 discussed the relationship of fire to
climate
• Forest Service Chief Tom Tidwell said, “Throughout the
country, we're seeing longer fire seasons, and we're seeing
snowpacks that, on average, are disappearing a little earlier
every spring," - As a result, fire seasons have lengthened by
more than 30 days, on average.
• He also cited devastating droughts
• "Our scientists believe this is due to a change in climate," said
Tidwell
54
Current Fire
Status
• IMT = Incident
Management
Team, 1 being
the worst fires
• Currently fire
level is
moderate (level
III)
55
Weather
Disasters
• The U.S. has seen twelve
weather-related disasters costing
at least $15 billion since 1980,
according to NOAA's National
Climatic Data Center (expressed
in 2012 $)
• Two of the top four most
expensive disasters have been
droughts
• The drought of 2012 was a $30.3 billion event, and cost 123 lives, according
to the National Climatic Data Center
• There were eleven billion dollar plus events in 2012
56