Transcript OVERVIEW OF CLIMATE SCIENCE

OVERVIEW OF CLIMATE
SCIENCE
What is the difference between
climate and weather?
Climate
A composite of a region’s average conditions
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)
Weather
Weather
• Shorter fluctuations lasting
– Hours
– Days
– Weeks
• Can refer to very short changes
Climates on Earth are Favorable to Life
• Surface Temperature
– Averages 15oC (59oF)
– Much of the Surface Ranges from
0o C to 30oC
Temperature Scales
• Kelvin Scale
– Divided into units of Kelvin
instead of degrees
– Absolute scale
• Converting values
between the Fahrenheit
and Celsius Scales
Tc = 5 (Tf – 32)
9
Tf = 9 (Tc + 32)
5
Geologic Time
 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 span<10
cm
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
• We will focus on the last several million years of Earth’s
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
Time Scales of Climate Change
Longest
Shortest
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
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.
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
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
Diversity of Studies
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Meteorology
Oceanography
Chemistry
Glaciology
Ecology
Geology
– Includes geophysics, geochemistry,
paleontology
• Climate Modelers
• Historians
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
Theories can be discarded
Ongoing work may disprove the
predictions of a current theory
An Historical Example . . .
The Geocentric Model of the Solar System
• Devised by Ptolemy (Claudius Ptolemaeus) in the
second century AD
• Accepted until 1543
The Heliocentric Model
replaced the Geocentric Model
Pluto is no longer considered a planet!
Pluto’s 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.”
Pluto is now considered a “Dwarf Planet”
• Pluto lost its status as a planet because
it’s highly eccentric orbit crosses over the
orbit of Neptune.
– As such it hasn’t “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
A Law or Unifying Theory
• If a theory has survived the test of time
– Years or decades
• It’s the closest approximation to “the truth”
as possible.
• It’s impossible to prove a theory as being
true.
• We can only prove it’s untrue.
Revolutions in Climate Change
• A scientific revolution that endeavors to
understand climate change has
accelerated.
• The mystery of climate change yields it’s
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.
Evolution
Evolution of the Jaw in Fish
Who is the Descendent of this Mammal?
Plate Tectonics
The unifying theory of geology
Tectonic Plate Boundaries
Earth’s Four Spheres
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Earth is divided into four independent parts
Each loosely occupies a shell around Earth - This why they’re called spheres
Earth Systems Interact
• Earth Systems Interact Video from the
American Geological Institute (AGI)
• http://www.youtube.com/watch?v=BnpF0ndXk8&list=PLTBBygdCOWWd-7-WOjPvPBSawmlvMoSDH
Earth’s Climate System
• Small number of
external factors
• Force or drive
changes in the
climate system
Earth’s Climate System
• Internal
components
respond to
external factors
• They change and
interact in many
ways
Earth’s Climate System
• End Result of
interactions
– A number of
observed
variations in
climate
– Can be measured
– Analogous to a
machine’s output
after input
(factors)
Studies of Earth’s Climate Cover a
Wide Range of Processes
Climate Forcing
Three fundamental kinds of
climate forcing
1. Tectonic Processes
• Part of Plate Tectonic Theory
• Alter the geography of Earth’s 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
2. Variations in Earth’s 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.
3. Changes in the Sun’s Intensity
• Affects the amount of solar radiation
arriving on Earth
• Long-term increase since Earth’s origin
• Shorter-term variations may be partially
the cause for changes on shorter time
scales of
– Decades
– Centuries
– Millenia
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
Climate System Responses
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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
Response Time
An Example . . .
• The rate at which water
in the beaker warms
– Water rises 50% towards
equilibrium during the
first response time
• As warming trend
continues
– Warming continues in
50% increments as the
water temperature
approaches equilibrium
Response Time
An Example . . .
• Each step takes one
response time.
– Moves the system half of the
remaining way towards
equilibrium.
• The total amount of
response time remaining
after each step is:
– ½, ¼, 1/8, 1/16
– This is an exponential change
• Rate slows as response
approaches equilibrium
Variation in the Response Times of
Climate System Components
Time Scales
of
Forcing Vs. Response
• Forcing is Slow in Comparison to Response
• Forcing is Fast in Comparison to Response
• Forcing and Response Time Scales are Similar
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
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 doesn’t respond
Fast Forcing in Comparison to Response
The Eruption of Mt. Pinatubo - 1991
• Earth’s 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
Similar Forcing and Response Time
Scales
• Bunsen Burner Analogy
– Abruptly turned on
• Left on for awhile
• Turned off
– Turned on again
• And so on . . .
Earlier
Time
Later
– Varying degrees of response
• Examples C and D
– Same equilibrium values
– Length of time heat is applied
varies
• C – Flame turned on and off
less frequently
• D – Flame turned on and off
more frequently
• In the natural world climate
forcing rarely acts in an “on-orof” way.
Similar Forcing and Response Time
Scales
• Climate forcing (Bunsen
Burner)
– Behaves as a “moving target”
Earlier
Time
Larger response as water has time to
reach values nearer equilibrium
• Climate system response
(temperature) never
Later
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
Smaller response as water has less time to
reach values nearer equilibrium
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.
• Actual examples;
– Daily and seasonal
changes in heating
• Time “lag” between
maximum and minimum
insolation and maximum
and minimum temperature
Cycles of Forcing and Response
• Larger climate change
– Slower cycles of 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.
Cycles of Forcing and Response
• Results from changes in Earth’s 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
Response Times Can Vary with an
Abrupt Change in Climate Forcing
For example:
Greenhouse
Warming causes
increased
temperatures
Ocean
surface
Ice sheets
• Climate responses can range from slow to fast within
different components of the climate system.
• Depends on their inherent response times.
Variations in Cycles of Response
• Some fast-response parts of the climate system
track right along with the climate forcing.
• Other slow-response parts lag behind the
forcing.
Variations in Cycles of Response
• Fast response
– Seasonal changes in tropical monsoons
• Slow response
– Ice sheets
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 slowresponse 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
This Has Happened in the Past
Pleistocene Ice Age: 20,000 years ago to 11,000 years ago
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
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
Climate Feedbacks
Processes that Alter Climate
Changes Already Underway
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.
Positive Feedback Example
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.
Negative Feedback Example
Quantifying Feedback
• Feedback Factor
– The strength of a feedback on temperature
Temperature Change with Feedback
f = Temperature Change without Feedback
• If no feedback exists: f = 1
• Positive Feedback: f >1
• Negative Feedback: f < 1