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Transcript
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