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Climate Change


Climate Change Lecture 6 March 4, 2010 * * * * * * * * * How will a potential global average warming affect climate? Land areas are going to warm more than ocean ... – PowerPoint PPT presentation

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Title: Climate Change

Climate Change
  • Lecture 6
  • March 4, 2010

Climate Change Assignment
  • Due next Thursday, March 11
  • 2-3 paper on climate change and your assigned
    greenhouse gas
  • Must use at least 3 sources and include Works
    Cited page
  • Be prepared to discuss climate change in class
  • More detailed description up on website

Weather vs. Climate
  • The difference between weather and climate is a
    measure of time
  • Weather is the state of the atmosphere, land, and
    ocean conditions on a day to day basis.
  • Most people think of weather in terms of
    temperature, humidity, precipitation, cloudiness,
    visibility, wind, and atmospheric pressure
  • Climate is the average weather in a location over
    a long period of time (months, years, decades,
  • Climate is what you expect, like a very hot
    summer. Weather is what you get, like a hot day
    with thunderstorms. 

Weather and Climate
  • Both weather and climate are influenced by a
    variety of factors such as
  • Astronomy (Earths tilt, rotation, distance from
    sun, and solar activity), terrain, location,
  • The Earths climate undergoes many natural
    changes and cycles

Why study climate?
  • Studying climate and a changing climate is
    important because it will affect people around
    the world
  • Rising global temperatures are expected to raise
    sea levels and change precipitation and other
    local climate conditions.
  • Changing regional climate could alter forests,
    crop yields, and water supplies. It could also
    affect human health, animals, and many types of

Global Climate Controls
  • Earths orbit and tilt
  • Land/sea distribution
  • Suns strength (long-term)
  • Earths albedo
  • ENSO
  • Greenhouse Gas Effect

Earths Orbit and Tilt
  • Orbit (Eccentricity)
  • How close is Earths orbit to circular?
  • Governs max. and min. distance from the sun
  • Orbit naturally fluctuates over 100s of thousands
    of years
  • Tilt (Obliquity)
  • Increased tilt increases seasonality
  • Tilt naturally fluctuates over tens of thousands
    of years

Land/Sea Distribution
  • Continents drift and shift over time (plate
  • Pangaea supercontinent that existed about 250
    million years ago
  • Affects ocean currents, wind patterns, etc
  • Continents are still moving today and will
    continue to shift

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Strength of the Sun
  • Sun goes through natural cycles of increasing and
    decreasing strength
  • These cycles are tens of thousands of years long
  • Sunspots follow a 11 year cycle (affects incoming
  • More output from sun ? warmer Earth

  • The Earth actually reflects much of the sunlight
    it receives
  • Light that in reflected back to space does not
    warm the Earth
  • The percent of sunlight the earth reflects is
    called the albedo
  • Changing this albedo changes the amount of energy
    from the sun that is absorbed by the Earth! (thus
    changing the climate)

What changes the albedo?
  • Increase in snow and ice cover
  • Increase in areas covered by sand
  • Deforestation
  • Increased cloud coverage and thickness
  • Volcanic eruptions (releases ash and small
    particles into atmosphere)
  • Changes in land cover (vegetation vs asphalt, etc)

  • El Niño Southern Oscillation
  • Defined together as a periodic change in the
    atmosphere and ocean of the tropical Pacific
  • El Niño and La Niña are the oceanic aspects of
    the phenomenon and the Southern Oscillation is
    the atmosphere aspect

  • El Niño and La Niña events are defined as warming
    or cooling of surface waters of the tropical
    central and eastern Pacific Ocean
  • Southern Oscillation is defined by the sign of
    the pressure difference between Tahiti and
    Darwin, Australia
  • The oscillation does not have a specific period,
    but occurs every three to eight years

ENSO Classification
  • A warming or cooling of at least 0.5 C (0.9F)
    averaged over the east-central tropical Pacific
  • When this temperature anomaly persists for five
    months or longer, it is called an El Niño or La
    Niña episode

El Niño
  • El Niño occurs during a time of suppressed trade
    winds (winds moving from the east to the west) at
    the equator
  • Causes a pool of warm water to collect in the
    eastern Pacific near S. America (water there is
    normally cool)
  • Changes global wind patterns and temperature,
    altering weather on global scale

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Moderate to Strong El Niño occurring now
Greenhouse Effect
  • The atmosphere itself absorbs almost none of the
    suns incoming radiation
  • The Earths surface absorbs part of the suns
    energy and warms
  • Greenhouse gases in the atmosphere act to trap in
    some of the longwave radiation leaving the Earth.
  • Without greenhouse gases, ALL of the energy
    radiated by the surface would escape to space

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Greenhouse Effect
  • The radiative equilibrium temperature of the
    earth with no atmosphere is 0F
  • ? Adding greenhouse gases increased the
    radiative equilibrium temperature to 59F
  • Main greenhouse gases Carbon dioxide, water
    vapor, methane
  • More greenhouse gases more energy kept at the
    Earths surface warmer average temperatures
  • We MUST have greenhouse gases in order to survive
    but we dont want too many because we will

  • This is a scientific fact!

Climate Change
  • Climate change is a change in the statistical
    distribution of weather over periods of times
    that range from decades to millions of year
  • Can happen in a variety of ways and variety of
    places (specific region or whole Earth)
  • One example that is the topic of concern right
    now is how the climate for the entire globe has
    become warmer.
  • A skeptic to the fact of global warming might say
    What about the temperature record in the
    interior of Antarctica where there is a cooling

History of Climate Science
  • Most people think global warming is a new theory
    - it is not!
  • Svante Arrhenius first theorized that surface
    temperatures would increase with increasing CO2
    concentrations in the 1890s

Early 1900s
  • Scientists ignored the theory, saying the ocean
    will suck up all of the CO2 we emit
  • The ocean has sucked up HALF of all human CO2
    emissions since the industrial revolution, but is
    becoming saturated

Global Warming Evidence
More Observations Has Led To Better Knowledge
Also http//
Observations of CO2 concentrations
  • Increase in greenhouse gases from 1700 to today
    results in 2.43 W/m2 more energy at the surface

CO2 accounts for 60 of the increase ? 1.46 W/m2
Recent Global Warming
  • CO2 has increased 25 in the last century and
    solar radiation incident on earth has slightly
  • Why has the rise in global temperatures been
    relatively small?
  • ? Reflective sulfate aerosols
  • Major volcanic eruptions between 1880 -1920 and
  • Sulfur particles into the stratosphere
  • ? lower the albedo ? cooling effect
  • Cooling effect (increased albedo)
  • Warming effect (increased greenhouse gases)
  • Small net warming

Climate Modeling The last 150 years
Projected Global Warming
  • Modeling the last 150 years, we have a good idea
  • Greenhouse gas emissions by humans
  • Vegetation changes
  • Future projections of climate change needs
    estimations of
  • Greenhouse gas emissions
  • Population changes
  • New technologies
  • Vegetation

Intergovernmental Panel on Climate Change
  • IPCC established in 1988 by the World
    Meteorological Organization and UN
  • Publishes special reports on topics relevant to
    climate change
  • Most of the observed increase in global average
    temperatures since the mid-20th century is very
    likely (90 likelihood) due to the observed
    increase in anthropogenic GHG concentrations.
  • The probability that this is caused by natural
    climatic processes alone is less than 5.- IPCC
    4th Assessment Report

Projected Global Warming
  • A2 ? Slow economic/technological growth, high
    population growth
  • A1B ? Rapid economic/technological growth,
    population peaks midcentury
  • B1 ? Medium population/economic growth,
    emphasizing local solutions and sustainability

How will a potential global average warming
affect climate?
  • Land areas are going to warm more than ocean
  • As snow-covered tundra melts, boreal forests will
    absorb 3 times as much solar energy
  • More frequent intense precipitation events and
  • Warmer air temperatures hold more water vapor
  • Polar front and jet will shift northward
  • Subtropical regions will be warmer and drier
  • Shift in mid-latitude weather systems northward
  • A warmer planet will see a rise in sea level.
  • Warmer water is thicker
  • Melting ice caps

Supporters of Global Warming and its Connection
to Increased Amounts of Greenhouse Gases say
  • The rise in CO2 and other greenhouse gases is
    definitely anthropogenic
  • Historical temperature records show an increase
    of 0.4-0.8oC in the last 100 years
  • This has been an unusually warm period when
    comparing it to the last 1000 years
  • CO2 is a first order forcing of climate change
  • There will be long term ramifications if we
    dont do something now!

Opponents of Global Warming and its Connection to
Greenhouse Gases Say
  • IPCC, and other atmospheric scientists, draw
    most of their conclusions from climate models.
    These models have major flaws with cloud physics,
    and dont necessarily include every kind of
    climate forcing!
  • On that note, climate models dont even include
    all climate feedbacks (ice-albedo feedback, etc.)
  • Just because weve observed the temperature to
    rise around the start of the Industrial
    Revolution doesnt necessary mean that increased
    fossil fuel use has caused the temperatures to
  • The observational records are flawed
  • The Earth has observed many climatic shifts of
    its history, some of which arent that well