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Lecture 6: Climate Change, Volume 1


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Title: Lecture 6: Climate Change, Volume 1

Lecture 6 Climate Change, Volume 1
  • Earths Climate Variability and
  • Reconstructing Previous Climates

Lecture 6, Volume 1 Outline
  • Earths Climate Variability
  • Factors That Affect Earths Climate
  • Ways of Measuring Past Climates

Global Temperature and Precipitation Change
over Geologic Time
This graph is the estimated global climate over
the Phanerozoic. The Red line represents Modern
Condie and Sloan, 1998
From the previous slide
  • Note the following
  • Since the formation of Earth, global climate has
    generally cooled
  • There are several instances where the Earths
    climate was warmer than today, such as during the
    Mesozoic and early Cenozoic.
  • There are several instances when the Earths
    climate was cooler than today, such as during the
    Ordovician, Permian, and most of the Quaternary

Global Temperature Change Over Time
A) 180 MYBP - Present
Isotope Substation 5e
B) 1 MYPB - Present
Mackensie (1999), Our Changing Planet
The Quaternary
  • Note that the Quaternary (last 1.8 million years)
    is characterized by climatic oscillations. These
    oscillations occur about every 100,000 years, and
    they are divided into two stages
  • Glacial stage when global climate is cooler
    lasting in duration for approximately 60,000
    90,000 years
  • Interglacial stage when global climates are
    warmer lasting in duration for approximately
    40,000 years to 10,000 years.
  • The most common glacial duration is 90,000 years
    in length and the most common interglacial
    duration is 10,000 years in length.

The Wisconsin Glaciation
  • The most recent glaciation is the Wisconsin
  • Glaciers advanced across North America around
    120,000 years ago. The maximum extent of
    glaciers occurred around 18,000 years ago (The
    Wisconsin Glacial Maximum, WGM). This is the
    period during the most recent glaciation when
    global temperatures where at their coolest
    (estimates are between 4C to 8 C cooler than
    today). Since that time, global temperatures
    have warmed, although the warming trend has not
    been consistently linear. Several blips in the
    warming trend are apparent, such as during the
    Younger Dryas period, ca. 14,500 years ago.

Wisconsin Glaciation Ice Sheets
Berengia Land Bridge
Ruddiman (2001) Earths Climate Past and Future
(pg. 303).
Polar Jet
Global Temperature Change Over Time
C) 100 K YR BP - Present
D) 18 K YR BP - Present
Mackensie (1999), Our Changing Planet
  • The last 10,000 years are characterized as the
    Holocene, the current interglacial period. The
    Holocene has climatic oscillations embedded
    within the overall warming period.
  • The Climatic Optimum (or Hypsothermal) was a time
    when global temperatures were ca. 4 warmer than
  • During 1000 AD, temperatures where again warmer
    than today. We know this from historical records
    of vineyards in England, Vikings colonizing
    Greenland, etc..
  • From 1300 mid 1800s climate in the Northern
    Hemisphere was colder than present. This time
    period is called the Little Ice Age

Warming trend
Note the warming trend after the Little Ice Age
Mackensie (1999), Our Changing Planet
Glacial Retreat in the French Alps following the
Little Ice Age
Glaciers advanced during the Little Ice Age in
the Alps.
1850 AD
1966 AD
Kump et al. (1999), The Earth System
Synopsis of the last few slides
  • The Earths climate is variable.
  • Currently we are in an interglacial cycle when
    temperatures are abnormally warmer than the
    Quaternary average
  • The interglacial cycles in the past have lasted
    10,000 years, the current interglacial is 10,000
    years in age.
  • Theoretically if the same processes that have
    been going on for the last 1.8 million years are
    still present (glacial/interglacial cycles), then
    by all accounts the next ice age should begin
    anytime now.
  • The climate over the last decade is warmer than
    it has been throughout the early Twentieth

What causes changes in global climate
  • Plate Tectonics The ocean currents redistribute
    heat on the planet. The current continental
    arrangement allows warm ocean currents (e.g. the
    Gulf Stream) to carry warm tropical waters to the
    polar regions and cool ocean currents (e.g. the
    California current) to carry cooler polar waters
    towards the tropics. This is possible because
    the continents are aligned in north-south
    orientation. When continents shift, as in the
    breakup of Pangaea, this poleward heat transfer
    is blocked. The absence of warm waters moving to
    the north is believed to instigate ice ages (like
    that in the Permian).

The Major Surface Ocean Currents Today
Continental arrangements are North - South
(McKnight, 1999)
Note how the position of the continents
interferes with the poleward heat transfer
The Breakup of Pangaea
(McKnight, 1999)
Changes in Solar Insolation
  • Variations in the Earths orbit affect the amount
    of sunlight. This is explained by the
    Milankovich cycles. I believe that you have had
    this in Geology 2 (according to Ms. Ruffin you
    remember her from the orientation DVD, she
    teaches a few TIG classes). Just as a review,
    Milankovitch describes three orbital changes
  • Eccentricity earth changes from circle to
    elliptical orbit -100,000 yr cycle
  • Tilt the Earths tilt wobbles from 21.5 to
    24.5 every 40,000 yrs.
  • Precession of the seasons, change in the
    direction the axis is pointing 20,000 yr cycle.
  • All these orbital changes affect solar
    insolation, which is related to changes in global

Milankovitch Cycle
Kump et al. (1999)
Atmospheric Gasses
  • Certain gasses in the atmosphere trap terrestrial
    radiation, analogous to a blanket.
  • CO2 especially
  • Review the Global Energy Balance and pay
    attention to the interaction of long-wave
    radiation and the atmosphere.
  • Theoretically by increasing or decreasing the
    concentration of greenhouse gasses will result in
    trapping more terrestrial heat or allowing more
    heat to escape to outer space, respectively.
    Thus the concentration of CO2 (and other gasses)
    affects global temperature.
  • From your textbook.

Figure 20-3
Current Warming Trend
  • It is believed by many (and refuted by many) that
    the recent warming trend is related to an
    increase in CO2 following the Industrial

Ways to Measure Previous Climates
  • Oxygen Isotope From Ice cores, cooler climates
    will have the lighter oxygen isotope (O16) in
    more abundance than the heavier O18. When its
    cooler, the lighter oxygen is evaporated
    preferentially the heavier oxygen stays in the
  • Marine sediments show the opposite trend.
  • Ice cores also trap minute gas bubbles. The gas
    bubbles can be used to measure the gas
    composition of the atmosphere when the ice layer
    was deposited.

Changes in the Oxygen isotopic Composition of
Seawater During the Growth of Continental Ice
Kump et al. (1999)
Ice Core
Deep Sea Cores
  • Evidence from the sediment cores (O18/O16 ratios
    in marine sediment) collected from the ocean
    depths reveal climate variability over the last
    700,000 years. This correlates nicely with
    climatic variability associated with Milankovich.

18O/16O Ratio from Deep-Sea Sediment Cores
Raymo (1994) Ann. Rev. of Earth Plan. Scil,
22353-383 taken from Kump et al. (1999), The
Earth System, pg 214
Vostok Ice Core
  • Cores from Antarctica also show climatic
    variability. They also show a highly correlative
    relationship between CO2 concentration (from the
    gas bubbles in the ice core) and temperature
    (from O18/O16 ratio in the ice).

CO2 (a) and Global Temperatures (b) from the
Vostock Ice Core
Note the Correlation Of CO2 And temp.
From R.W. Christopherson, Geosystmes AN
Introduction to Physical Geography, 3/e, 1997.
Reprinted by permission of Prentice Hall, Upper
Saddle River, N.J.) taken from Kump et al.
(1999), pg 221.
Other Paleoclimate Methods
  • Palynology the study of pollen. Pollen
    preserved in lake sediments (and other
    environments) is reflective of the vegetation
    around the lake when it was deposited.
    Determining the type and amount of each pollen
    type can allow scientists to determine vegetation
    changes, such as from forest to grassland or from
    tundra to forest.
  • Vegetation is strongly linked to climate. So the
    fossil pollen grains are records of previous

Various Pollen Types
Bush (1999)
Sediment Core from Dukes Pond, GA
My Colleague Andrew Ivester (West Georgia
University) and I collecting Sediment cores for
pollen analysis in southeastern Georgia
Pollen is preserved in The anaerobic, mucky soils
4000 years ago
Pollen Diagram for Silver Lake, Ohio
Mixed Deciduous Forest
Boreal forest
Note the change in pollen types around 12,000
years. What do you Think would be causing this
change? Retreat of the glaciers perhaps?
Bush (1999)
  • The width of annual rings in trees are strongly
    reflective of the environment the tree is growing
  • Note Trees in more marginal or stressful
    habitats are more sensitive to environmental
  • Not all trees produce visible annual rings. Some
    wood types (hardwoods especially) have an
    abundance of a plant tissue called vessel
    members which obscure annual rings. Usually the
    conifers, which lack vessel members, have the
    clearest ring development.

Extruding core from borer
Me coring a tree on South Core Banks Island, NC.
I was much younger And enthusiastic back then!
Some trees are really old
  • Trees out west can be very old. The bristle cone
    pine, for example, has a life span of several
    thousands of years.
  • Tree rings from these old individuals can push
    the climatic record back to thousands of years.
  • Dendrochonology is really cool because it allows
    you to see annual climatic changes. Pollen
    analysis on the other hand can go back further in
    time (last couple hundred thousands of years) but
    it has a very coarse resolution maybe the last
    50 or 100s of years get blended.

Bristlecone Pine - Oldest living tree, 4900 years
Conclusion of Volume 1
  • The Earths climate is variable. I want you to
    be aware of how it varies because I believe that
    it will help you understand the current global
    warming debate.
  • In discussing the future state of the planet, I
    believe that we must have a working knowledge of
    what has gone on in the past.
  • From this part of the lecture I want you to be
    able to recognize important climatic time periods
    (Wisconsin Glacial Max, Holocene, Hypsothermal,
    Little Ice Age, etc.) understand the climatic
    oscillations that have occurred in the past and
    understand a little about how these climatic
    variations have been estimated.

Lecture 6 Climate Change, Volume 2
  • Current Global Climate Change Debate

Lecture 6, Volume 2 Outline
  • Current Trends
  • Temperature
  • Carbon Dioxide
  • Consequences of a warmer planet
  • Sea Level
  • Hurricanes
  • Uncertainties with feedback loops
  • Government Panels on Climate Change
  • Concluding Remarks

A set of temperature records from over 7,000
stations around the world has been compiled by
the NOAA National Climate Data Center to create
the Global Historical Climatology Network - GHCN
(GHCN Version 2 data set Peterson and Vose
1997). About 1,000 of these records extend back
into the 19th century.
Satellite Data from NOAA
  • The current rate of warming is 0.06C per decade,
    which is slower than ground-based thermometers
    (NOAA, 2006). It is unclear why the satellite
    and ground thermometers show discrepancies.

Current Trends
  • For the last 100 years or so global temperatures
    have warmed

Sea Surface Temperatures have also been rising
In addition to higher temperatures, the
atmospheric concentration of CO2 has also
increased in the last 100 years
  • Current CO2 concentrations are

Cloud Cover has also increased
Northern Hemisphere during the past century
(Groisman, 1999). While water vapor is the most
abundant greenhouse gas, low clouds also shade
and cool the surface. Currently the role that
water vapor and clouds play in warming or
cooling the Earth's climate system is being
Earths Climate is Changing?
  • So there are signs that the global temperatures
    are warming, especially over the last 100 years.
    I dont think too many people would argue against
  • Is this directly related to elevated atmospheric
    CO2? Are there feedback mechanisms to mitigate
  • Is this part of a significant warming trend or is
    this just background noise in a complex time
  • These are questions that are difficult to answer
    with any certainty, at least at this time.

What are the consequences of a warmer climate?
  • The most noted global change from a warmer planet
    is a rise in sea level. Currently the global sea
    level is rising at a rate of 2mm/year.
  • Sea level rises due to
  • Glacio-Eustatic changes
  • Thermal expansion
  • Changes in ocean shape

Sea Level Rise, US Rates
Davis and Fitzgerald, 2002 Beaches and Coasts.
Ice Sheet
  • The two large ice sheets, Greenland and
    Antarctica, contain enormous volumes of water.
    Should these glaciers melt, then sea level would
  • If Greenland melted sea level would rise by as
    much as 7 feet.
  • IF Antarctica melted, sea level would rise by as
    much as 70 feet.

Greenland and Antarctica Ice
  • Currently the Greenland Ice sheet is melting.
    The Jakobshavn Isbrae doubled its meltwater flow
    from 1997 2003, and this influx of meltwater
    has caused a measurable rise in sea level (The
    Heat is On, The Economist, Vol 380, No. 8494 pg
  • The western Antarctic ice sheet, Larsen B, is
    also melting (The Economist article cited above).
  • Will this trend continue? Is this part of a
    natural glacial cycle? Is this related to the
    current global warming trend? Should we be
    preemptive and purchase beach front property in
    Iowa? How much will this affect global sea
    level? There is still a large degree of
    uncertainty, more research is needed.
  • In any event, with higher sea level countries
    such a Bangladesh, The Bahamas, and much of the
    Atlantic Seaboard and Gulf Coasts are in trouble.

Themohalocline Circulation
  • Related to the melting of ice is the risk of
    interrupting the Thermohaline Circulation

Thermohaline Circulation
The Concern
  • The concern is that cool, freshwater melting off
    of the Greenland glacier will interrupt the
    Thermohaline circulation. An influx of cold
    freshwater would eliminate the halocline gradient
    and the warm Gulf Stream would cease flowing
    northward. This would act like a positive
    feedback loop in which the cooler ocean
    temperatures may spawn another ice age.
  • The influx of cold water is thought to have been
    responsible for the reversal of the post-glacial
    warming trend around 14,500 years ago (aka the
    Younger Dryas Period). The blip in the warming
    trend after the Laurentide glacier retreated may
    be related to an influx of cold, freshwater in
    the Northern Atlantic.

Younger Dryas Example of when the Thermohaline
Circulation stopped - from the influx of glacier
It took the Earth several thousand Years to
yas _octopetala_Roger_Johansen.jpg
Other Concerns about a Warming Planet
  • Hurricanes and Severe Weather.
  • Most of the increase in hurricane size and
    periodicity (Hurricane Katrina) is related to
    decadal oscillations (AMO), and not really
    associated with global warming.
  • Some researchers believe that larger and more
    hurricanes are inevitable during a warmer
    climate. Dr. Kerry Emanuel at MIT suggested
    that the intensity of Atlantic storms had on
    average doubled over 30 years (The Economist,
    Vol. 384 pg 12).
  • The Tropical Storm Zeta on 12/31/05 may be
    evidence of an extended hurricane season.

Other Concerns
  • There are far too many other topics to include.
    As a shortened summary, other factors that may be
    affected by global warming
  • Changing distribution of organisms (Red fox are
    now competing with Artic fox in Alaska).
  • Effects on agriculture. Russia would benefit as
    more agricultural land would be exposed the US
    might suffer with hotter/drier conditions.
    England is now growing wine again (hasnt
    occurred since Medieval periods.

Review to this point
  • The Earths climate is getting warmer, but the
    length of this warming trend and the consequences
    that this warming trend will have are debatable.
  • The Earth-Atmosphere system is extremely complex,
    more so then we can understand. Several
    uncertainties exist regarding how the Earth will
    react to increasing temperatures

  • The baffling complexity of the climate-and thus
    the difficulty of predicting what is going to
    happen to it-arises principally from its feedback
    loops (The Heat is On The Economist, Vol.
    384, pg. 4). The following feedbacks are
    reported from the above issue
  • Albedo with an increase in ice and the
    resulting increase in the worlds albedo, more
    solar radiation should be reflected back to
    space. Thus there would be a positive feedback
    of global cooling. The converse would be that
    the reduction of glaciers would decrease the
    albedo, resulting in more solar radiation being
  • Ocean Absorption CO2 is more soluble in water
    in colder temperatures. As sea surface
    temperatures warm, the oceans ability to store
    CO2 would be lessened. This would be a positive
    feedback in which a warmer ocean would release
    more CO2, and in turn this would blanket the
  • Soil Respiration Warming leads to more
    microbial activity, which in turn produces more
    CO2 (via cellular respiration).
  • Clouds Clouds could be a positive or negative
    feedback. By positive feedback a warmer
    climate produces more clouds that trap more solar
    radiation. Conversely the negative feedback
    could be a warmer climate produces more clouds,
    more clouds increases the atmosphere's albedo,
    which reflects more solar energy. This would
    result in a cooling trend

  • In addition to the complexity in understanding
    the feedback mechanisms, there are other factors
    that need to be accounted for.
  • For one, temperature data over the last several
    hundred years has some inconsistencies
  • Thermometers have become more accurate and more
    precise over time. Data from the early part of
    the century may not be at the same accuracy level
    as modern measurements.
  • Areas have become more urban over time. The same
    thermometer may be reading warmer values in more
    recent times do to the increased urbanization
    (and resulting urban heat island). The warming
    trend , then, is more a reflection of
    urbanization than global warming.
  • Weather stations have moved. See Dr. Barry
    Keims research (LSU, and Louisiana State
    Climatologist) on what affect NWS station
    relocations have had on temperature measurements.
  • I bring up these points to illustrate an
    important point there are a lot of factors that
    have to be considered when examining global
    climate change, regardless of whether you are on
    one side or the other. It is not a simple, cut
    and dry issue. I am neither ruling the current
    global warming trend out or advocating it, but
    instead suggesting that more research is needed.

Government Responses
  • What is the government doing about climate
  • There are several US Government agencies
    monitoring climate change.
  • There is even a US law that states the US Govt.
    must be cognizant of climate change.

  • The U.S. Climate Change Science Program (CCSP)
    was launched in February 2002 as a collaborative
    interagency program, under a new cabinet-level
    organization designed to improve the government
    wide management of climate science and
    climate-related technology development.
  • Quote from the CCSP website.

U.S. Global Change Research Act of 1990Public
Law 101-606(11/16/90) 104 Stat. 3096-3104
  • An Act To require the establishment of a United
    States Global Change Research Program aimed at
    understanding and responding to global change,
    including the cumulative effects of human
    activities and natural processes on the
    environment, to promote discussions toward
    international protocols in global change
    research, and for other purposes.
  • Government definition of "Global change" means
    changes in the global environment (including
    alterations in climate, land productivity, oceans
    or other water resources, atmospheric chemistry,
    and ecological systems) that may alter the
    capacity of the Earth to sustain life

Other US Govt. Agencies
  • In addition to the previous, other agencies are
    responsible for keeping an eye out on global
    climate change. Perhaps the most noted is NOAAs
  • The Climate Program Office (CPO), created in
    October 2005, incorporates the Office of Global
    Programs, the Arctic Research Office, and the
    Climate Observations and Services Program and,
    coordinates climate activities across all NOAA.
    The new CPO focuses on developing a broader user
    community for climate products and services,
    provides NOAA a focal point for climate
    activities within NOAA, leads NOAA climate
    education and outreach activities, and
    coordinates international climate activities.
  • NOAA's Climate goal is to "Understand and
    describe climate variability and change to
    enhance society's ability to plan and respond".

State Law California
  • On August 31, 2006 the California legislature
    passed a bill establishing the most extensive
    carbon dioxide (CO2) emission controls yet in the
    United States. The law requires a 25 percent
    reduction in state CO2 emissions by 2020, with
    the first major controls taking effect in 2012.
    The California Air Resources Board, the agency
    that enforces the states air pollution controls,
    will be the main authority in establishing
    emission targets and noncompliance penalties for
    the law, which also allows for business
    incentives to reach the goals.

Global UNs IPCC
  • The Intergovernmental Panel on Climate Change
  • "The role of the IPCC is to assess on a
    comprehensive, objective, open and transparent
    basis the scientific, technical and
    socio-economic information relevant to
    understanding the scientific basis of risk of
    human-induced climate change, its potential
    impacts and options for adaptation and
    mitigation. IPCC reports should be neutral with
    respect to policy, although they may need to deal
    objectively with scientific, technical and
    socio-economic factors relevant to the
    application of particular policies. Review is
    an essential part of the IPCC process. Since the
    IPCC is an intergovernmental body, review of IPCC
    documents should involve both peer review by
    experts and review by governments"

The Kyoto Protocol
  • Meeting of 160 countries in 1997 to discuss
    measures to mitigate CO2 emissions. The
    international treaty to reduce greenhouse gasses
    took affect in 2005.
  • "stabilization of greenhouse gas concentrations
    in the atmosphere at a level that would prevent
    dangerous anthropogenic interference with the
    climate system" UNFCCC-2. Quote taken from
  • The US and Australia did not participate and will
    not ratify the CO2 reduction legislation. Some
    of the US disagreements with the legislation are
    (1) it exempts China (the second largest producer
    of CO2) and (2) economic concerns. The absence of
    US participation (the largest CO2 producer)
    raises serious questions about the effectiveness
    of the Kyoto Protocol.

Concluding Remarks
  • What do I hope that you got from Lecture 6
  • A realization that the Earths climate changes.
    There are cooling periods and warming periods,
    and this is not uncommon during our planets
  • Changing climate can have really severe
    implications. This is a topic that is certainly
    worthy of attention.
  • There is a great deal of uncertainty regarding
    global climate change. There are several climate
    interactions that are not fully understood.
    There are also several inconsistencies with our
    data. These factors must be taken into
  • More research is needed. Global climate change
    is important and it could have severe
    consequences to our society. It is not to be
    taken lightly. Media hype and bad science may be
    misleading, confusing, and may be polarizing our
    society more than it needs. We need careful
    observations and unbiased interpretations.
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