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					Climate Change

    Lecture 13
 December 2, 2009
  Climate Change Assignment
• Due next Wednesday, December 9
• 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
       Review from last week
In a cold cloud, all precipitation begins in the
  form of snow (ice crystals)
• 5 Main Precipitation Types
  1. Rain  drops of liquid water
  2. Snow  ice crystals
  3. Sleet  frozen rain drops
  4. Freezing Rain  rain the freezes on
                 contact with a cold surface
  5. Hail  large pieces of ice

How do we get this variety if the origin of the
 precipitation is the same?
                     Snow
• The surface temperature is
  25°F (-4°C) and increases
  with height before
  decreasing.
• However, since the
  temperature remains below
  freezing at every height, any
  precipitation that falls will
  remain as snow.


                             http://www.srh.noaa.gov/jetstream//synoptic/precip.htm
• Flurries - Light snow falling for short
  durations. No accumulation or light dusting
• Showers - Snow falling at varying intensities
  for brief periods of time. Some accumulation
  is possible.
• Squalls - Brief, intense snow showers
  accompanied by strong, gusty winds.
  Accumulation may be significant. Snow
  squalls are best known in the Great Lakes
  region.
• Blowing Snow - Wind-driven snow that
  reduces visibility and causes significant
  drifting.
• Blizzard - Winds over 35 mph with snow and
  blowing snow reducing visibility to less than
  ¼ mile for more than 3 hours.
                         Sleet
• Surface is below freezing
• As snow falls into the layer of
  air where the temperature is
  above freezing, the snow flakes
  partially melt.
• As the precipitation reenters the
  air that is below freezing, the
  precipitation will re-freeze into
  ice pellets that bounce off the
  ground, commonly called sleet.
• The most likely place for
  freezing rain and sleet is to the
  north of warm fronts. The cause
  of the wintertime mess is a
  layer of air above freezing aloft.

                                  http://www.srh.noaa.gov/jetstream//synoptic/precip.htm
                   Freezing Rain
• Freezing rain will occur if
  the warm layer in the
  atmosphere is deep with
  only a shallow layer of
  below freezing air at the
  surface.
• The precipitation can begin
  as either rain and/or snow
  but becomes all rain in the
  warm layer.
• The rain falls back into the
  air that is below freezing but
  since the depth is shallow,
  the rain does not have time
  to freeze into sleet.
• Upon hitting the ground or
  objects such as bridges and
  vehicles, the rain freezes on
  contact.
                                   http://www.srh.noaa.gov/jetstream//synoptic/precip.htm
        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, etc)
• 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 (Earth’s tilt, rotation, distance
  from sun, and solar activity), terrain,
  location, humans
• The Earth’s climate undergoes many
  natural changes and cycles
         Why study climate?
• The reason studying climate and a
  changing climate is important, is that 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 ecosystems.
        Global Climate Controls
•   Earth’s orbit and tilt
•   Land/sea distribution
•   Sun’s strength (long-term)
•   Earth’s albedo
•   ENSO
•   Greenhouse Gas Effect
               Earth’s Orbit and Tilt
• Orbit (Eccentricity)
  – How close is Earth’s 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
  tectonics)
• 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
            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
  radiation)
• More output from sun 
  warmer Earth

                              http://science.howstuffworks.com/sun.htm/printable
                      Albedo
• 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)
                 ENSO
• El Niño Southern Oscillation
• Defined together as a periodic change in
  the atmosphere and ocean of the tropical
  Pacific region
• El Niño and La Niña are the oceanic
  aspects of the phenomenon and the
  Southern Oscillation is the atmosphere
  aspect
                  ENSO
• 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
  (0.9°F) averaged over the east-central
  tropical Pacific Ocean
• 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
El Niño occurring now
         Greenhouse Effect
• The atmosphere itself absorbs almost
  none of the sun’s incoming radiation
• The Earth’s surface absorbs part of the
  sun’s 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
         Greenhouse Effect
• The radiative equilibrium temperature of
  the earth with no atmosphere is 0°F
  ➔ Adding greenhouse gases increased
  the radiative equilibrium temperature to 59°F
• Main greenhouse gases: Carbon dioxide,
  water vapor, methane
• More greenhouse gases = more energy kept
  at the Earth’s surface = warmer average
  temperatures
• We MUST have greenhouse gases in order
  to survive but we don’t want too many
  because we will overheat
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 trend?”
        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 1900’s

• 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




http://www.globalwarmingart.com/wiki/Image:2000_Year_Temperature_Comp
arison_png

                                                       Also: http://data.giss.nasa.gov/gistemp/graphs/
  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
  increased
• Why has the rise in global temperatures been
  relatively small?
  → Reflective sulfate aerosols
  – Major volcanic eruptions between 1880 -1920 and
    1960-1991
  – 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 of
  – 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
• Assessment based on peer reviewed and
  published scientific literature
• “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
  areas
  – As snow-covered tundra melts, boreal forests will
    absorb 3 times as much solar energy
• More frequent intense precipitation events and
  flooding
  – 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
 don’t 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 don’t
necessarily include every kind of climate forcing!
• On that note, climate models don’t even include all
climate feedbacks (ice-albedo feedback, etc.)
•Just because we’ve observed the temperature to rise
around the start of the Industrial Revolution doesn’t
necessary mean that increased fossil fuel use has caused
the temperatures to increase
•The observational records are flawed
• The Earth has observed many climatic shifts of its
history, some of which aren’t that well understood

				
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