Ice Ages and Climate Change - Florida Atlantic University
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Transcript Ice Ages and Climate Change - Florida Atlantic University
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
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