OVERVIEW OF CLIMATE SCIENCE

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OVERVIEW OF CLIMATE SCIENCE
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What is the difference between climate and
weather?
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Climate A composite of a regions average
conditions
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Climate

• Applies to long-term changes
• Measured in terms of
• Temperature
• Precipitation
• Snow and ice cover
• Winds
• Can refer to
• The entire planet
• Specific regions (continents or oceans)

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Weather
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Weather

• Shorter fluctuations lasting
• Hours
• Days
• Weeks
• Can refer to very short changes

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Climates on Earth are Favorable to Life

• Surface Temperature
• Averages 15oC (59oF)
• Much of the Surface Ranges from 0o C to 30oC

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Temperature Scales

• Kelvin Scale
• Divided into units of Kelvin instead of degrees
• Absolute scale
• Converting values between the Fahrenheit and
  Celsius Scales
• Tc (Tf 32)
• Tf (Tc 32)

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Geologic Time
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• 1 km 1 million years
• LA to NY 4,500 million yrs
• Precambrian LA to Pittsburgh, PA
• Paleozoic entirely in PA
• Mesozoic 179 km drive to NJ, 65 from NYC
• End of ice age 10 m from destination
• 2,000 AD years is 2 meters
• Human life spanlt10 cm

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Another Geologic Time Analogy . . .

• If all Earth history had been recorded from its
  origin to the present as a motion picture
• Each frame would flash on the screen for 1/32 of
  a second which would equal 100 years
• To show all Earth history would take 16 days.
• The last 2,000 years would take ¾ of a second
• The present to the last ice age would be less
  than 7 seconds.
• The last 65 million years would take almost six
  hours
• The Paleozoic Era would last two days

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• We will focus on the last several million years
  of Earths history (about 10 of its total age)
• This can only be represented by
• A series of magnifications
• Using a log scale that increases by factors of 10

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Time Scales of Climate Change
Longest
Shortest
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Tectonic Change The Longest Time Scale

• Shows a slow warming
• Between 300 Myr and 100 Myr
• Last 100 million years
• Gradual Cooling
• Led to ice ages during the last 3 million years
• Note shorter oscillations

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Time Scales of Climate Change

• As the time scales become shorter
• Progressively smaller time scales are magnified
  out from the larger changes at longer time scales.

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Degree of Resolution

• Amount of detail retrieved from records
• Older records have less resolution
• Long term averages over millions of years
• Younger records have progressively greater
  resolution
• Shorter term averages
• Occur within intervals of
• Thousands
• Hundreds
• Even tens of years

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Development of Climate Science
National Center for Atmospheric Research Boulder,
CO

• Modern climatology is an interdisciplinary
  endeavor throughout the world
• Universities
• National Laboratories
• Research Centers

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Diversity of Studies

• Meteorology
• Oceanography
• Chemistry
• Glaciology
• Ecology
• Geology
• Includes geophysics, geochemistry, paleontology
• Climate Modelers
• Historians

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Studying Climate Change The Scientific Method

• Hypothesis
• An informal idea that has not been widely tested
  by the scientific community
• Most are discarded.
• Theory
• When a hypothesis is capable of explaining a wide
  array of observations.
• Additional observations support the theory
• New techniques for data analysis
• Devise models

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Theories can be discarded

• Ongoing work may disprove the predictions of a
  current theory

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An Historical Example . . .The Geocentric Model
of the Solar System

• Devised by Ptolemy (Claudius Ptolemaeus) in the
  second century AD
• Accepted until 1543

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The Heliocentric Model replaced the Geocentric
Model
Pluto is no longer considered a planet!
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Plutos Been Demoted!

• On August 24, 2006 the International Astronomical
  Union redefined the definition of a planet as
• a celestial body that is in orbit around the sun
• has sufficient mass for its self-gravity to
  overcome rigid body forces so that it assumes a
  nearly round shape,
• and has cleared the neighborhood around its
  orbit.

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Pluto is now considered a Dwarf Planet

• Pluto lost its status as a planet because its
  highly eccentric orbit crosses over the orbit of
  Neptune.
• As such it hasnt cleared the neighborhood
  around its orbit.
• A dwarf planet like Pluto is
• Any other round object that
• Has not cleared the neighborhood around its
  orbit
• Is not a satellite

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A Law or Unifying Theory

• If a theory has survived the test of time
• Years or decades
• Its the closest approximation to the truth as
  possible.
• Its impossible to prove a theory as being true.
• We can only prove its untrue.

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Revolutions in Climate Change

• A scientific revolution that endeavors to
  understand climate change has accelerated.
• The mystery of climate change yields its secrets
  slowly.
• This revolution has achieved the status so that
  it has begun to take its place alongside two
  great earlier revolution in knowledge of Earth
  history.

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Evolution
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Evolution of the Jaw in Fish
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Who is the Descendent of this Mammal?
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Plate Tectonics
The unifying theory of geology
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Tectonic Plate Boundaries
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Earths Climate System

• Small number of external factors
• Force or drive changes in the climate system

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Earths Climate System

• Internal components respond to external factors
• They change and interact in many ways

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Earths Climate System

• End Result of interactions
• A number of observed variations in climate
• Can be measured
• Analogous to a machines output after input
  (factors)

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Climate Forcing

• Three fundamental kinds of climate forcing

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1. Tectonic Processes

• Part of Plate Tectonic Theory
• Alter the geography of Earths surface
• Changes in distribution of land and sea
• Changes in surface topography
• Formation of mountain ranges
• Erosion of the land surface
• Slow processes
• Occur on a scale of millions of years

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2. Variations in Earths Orbit

• Alter the amount of solar radiation received on
  Earth
• By season
• As a function of latitude
• Occur over tens to hundred of thousands of years.

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3. Changes in the Suns Intensity

• Affects the amount of solar radiation arriving on
  Earth
• Long-term increase since Earths origin
• Shorter-term variations may be partially the
  cause for changes on shorter time scales of
• Decades
• Centuries
• Millenia

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A Fourth Factor to be Considered

• Anthropogenic Forcing
• In a strict sense, not part of the natural system
• The effect of humans on climate
• Unintended byproduct of agricultural, industrial,
  and other human activities
• Results from additions of materials to the
  atmosphere

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Climate System Responses

• Changes in global and regional temperatures
• Extent of ice
• Amounts of rainfall and snowfall
• Wind strength and direction
• Ocean circulation
• At Depth
• At the surface
• Vegetation
• Types
• Amount

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Response TimeAn Example . . .

• The rate at which water in the beaker warms
• Rate slows with time

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Response TimeAn Example . . .

• Equilibrium is reached
• Rate slows as response nears this state

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Variation in the Response Times of Climate System
Components
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Time Scales ofForcing Vs. Response

• Forcing is Slow in Comparison to Response
• Forcing is Fast in Comparison to Response
• Forcing and Response Time Scales are Similar

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Slow Forcing in Comparison to Response
Earlier Time
Later

• Response keeps pace with gradual forcing (i.e.,
  Equivalent to slowly increasing the bunsen burner
  flame.)
• Typical of tectonic scales of climate change
• Climate changes in response to movement of
  landmasses
• 1 degree of latitude per million years (100
  km/million years)
• Slow changes in solar heating
• Average temperature over the continent keeps pace
  with average changes in solar radiation because
  of the short response time of land and water

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Fast Forcing in Comparison to Response
Earlier Time
Later

• Response time of the climate system is much
  slower than the time scale of the change in
  forcing
• Little or no response
• Analogous to turning the Bunsen burner on and off
  so quickly that temperature doesnt respond

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Fast Forcing in Comparison to ResponseThe
Eruption of Mt. Pinatubo - 1991

• Earths average temperature decreased by 0.5o C
  in less than a year
• Most of the fine dust remained aloft for only a
  few years
• No long-term climate change

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Similar Forcing and Response Time Scales

• Bunsen Burner Analogy
• Abruptly turned on
• Left on for awhile
• Turned off
• Turned on again
• And so on . . .
• Varying degrees of response
• In the natural world climate forcing rarely acts
  in an on-or-of way

Earlier Time
Later
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Similar Forcing and Response Time Scales

• Climate forcing (Bunsen Burner)
• Behaves as a moving target
• Climate system response (temperature) never
  catches up
• lags behind
• Continuously changing series of equilibrium
  values
• Created by the moving target of climate forcing
• Rate of response is always fastest when the
  system is farthest from equilibrium

Earlier Time
Later
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Cycles of Forcing and Response

• Response to a moving target forcing is usually
  cyclic
• Fundamentally the same as the physical response
  of the beaker of water.

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Cycles of Forcing and Response

• Larger climate change
• The climate system has ample time to respond
• The same amplitude of forcing produces
• Smaller climate changes if the climate system has
  less time to respond.

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Cycles of Forcing and Response

• Results from changes in Earths orbit
• Over tens of thousands of years
• The climate response time characteristic of large
  ice sheets that advance and retreat
• Characteristic of Seasonal time lags between
• Highest solar intensity and hottest temperatures
• Lowest solar intensity and lowest temperatures

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Response Times Can Vary with an Abrupt Change in
Climate Forcing

• Climate responses can range from slow to fast
  within different components of the climate
  system.
• Depends on their inherent response times.

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Variations in Cycles of Response

• Some fast-response parts track right along with
  the climate forcing.
• Other slow-response parts lag behind the forcing.

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Variations in Cycles of Response

• Fast response
• Seasonal changes in tropical monsoons
• Slow response
• Ice sheets

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Variations in Cycles of Response
Single point of time - A huge ice sheet in
Canada and northern U.S.

• Low position of asterisk on the cold
  slow-response curve
• Ice sheet is at its maximum size
• Heating from the Sun has begun a slow, long-term
  increase
• Has not yet begun to melt any of the ice

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This Has Happened in the Past
Pleistocene Ice Age 20,000 years ago to 11,000
years ago
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Two Possible Responses of Air Temperatures Over
Land South of the Ice Sheet
Single point of time - A huge ice sheet in
Canada and northern U.S.

• Would air warm with slow increase of solar
  radiation?
• Climate response would track right along with the
  initial forcing curve
• Would air temperature still be affected by the
  ice sheet?
• If so, the response might follow a slower,
  delayed response pattern of the ice.
• The ice would also be exerting and influence of
  its own

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Both Explanations are Sound and Plausible

• The response of air temperatures could be
  influenced by both the Sun and the ice.
• Then, the air temperature response would fall
  between the fast and slow responses.
• Faster than the response of the ice
• Lagging behind the forcing of the Sun

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Climate Feedbacks

• Processes that Alter Climate Changes Already
  Underway

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Positive Feedback

• Produces additional climate beyond that caused by
  the original factor
• Amplifies change underway
• Not to be interpreted as a good change.
• Example
• Decrease in solar energy could result in glaciers
  at high latitudes
• Increase in ice and snow cover could further
  result in lower temperatures.

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Negative Feedback

• Climate change is muted.
• Not to be considered a bad change.
• After initial climate change is triggered, some
  components of the climate system reduce it.
• Example
• Effect of clouds on warming effects of increasing
  CO2 in the atmosphere.