Transcript Week 10 Review

Poster day
Good posters!
 Grades will be posted on web
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Based on poster score, bibliography score
and your evaluations
Anyone missing a textbook?
EXAM
Monday, June 4, 8:30 – 10:20 AM
 BE THERE!
 Do NOT tell me that you overslept, had a
hangover, were in the hospital with an
ingrown toenail, etc.
 If you have a LEGITIMATE excuse for
missing the final (and it is hard to imagine
one), email or talk to Prof. Ackerman on
MONDAY, no later!
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EXAM
Cumulative
 Slightly heavier focus on material since
last midterm (ozone, global warming)
 No questions on posters
 Similar in style to mid-terms
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Grade distribution (on web page)
W-credit
no-W-credit
Poster projects
10%
15%
Writing paper
10%
n/a
In-class activities
20%
20%
Homework
15%
20%
Mid-terms
25%
25%
Final
20%
20%
Extra Credit
up to 10%
up to 10%
Review
A Crash Course in Climate!
9 weeks x (120 slides / week) = 1080 PPT slides
Discount ~ 10% for announcements, duplication, etc
=> ~ 1000 slides to review!
What you should get from this class?
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General understanding of how the Earth climate
system works
Appreciation for how the scientific process works
Learn how to critically evaluate what you hear
about climate and climate change
Where did we start?
Climate as system
 Energy balance
 Daisyworld
 Earth climate forcing and feedbacks
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Our First Equation!
Energy Balance Theory of Climate Change
T = λ F
F = Forcing (change in energy balance)
T = Response (change in surface temp)
λ = Climate sensitivity (determined by
feedbacks)
Daisy
world
So what did we learn from Daisyworld?
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Introduced a lot of core ideas
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Planetary albedo and energy balance
Climate forcing and system response
Positive and negative feedbacks
Stable and unstable equilibria
Lessons
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Biology matters to climate
Climate system can be “self-regulating”
Self-regulation is imperfect (has limits)
EM Radiation and Matter
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Interact in 4 ways
Radiation encountering matter
(molecules in air, liquid or solid) can be
1.
2.
3.
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Absorbed
Transmitted
Scattered (reflected, but a bit more
complicated)
ALL matter emits radiation
4.
Emitted by matter
Planetary Energy Balance
SO (1 – A) πR2 = σ TE4 4πR2
Now divide both sides by surface area of sphere (4πR2) to
get energy fluxes averaged over the earth surface
SO (1 – A) / 4 = σ TE4
Greenhouse Effect
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If the earth had the same albedo (0.3) and NO
atmosphere, surface temperature would be 255 K
The atmosphere acts like a blanket (sort of) around the
earth trapping heat (sort of) and keeping the surface warm
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Magnitude of the greenhouse effect, TG, is
TG = TS - TE
TG = 288 - 255 = 33 K
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TG is a property of the atmosphere (atmosphere effect?)
Cloud Forcing
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What is the sign for current climate?
Negative => clouds cool planet
 Positive => clouds warm planet
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Answer: Clouds cool the planet
SW forcing is larger (in absolute sense) than
LW forcing
Examples of Earth climate feedbacks
Ice – albedo
 Water vapor feedback
 Cloud feedback
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Shortwave
 Longwave
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Where to next?
Atmosphere circulation
 Ocean circulation
 Can we model this mess?
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Earth as heat engine
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Atmosphere and ocean currents move heat from
equatorial regions to polar regions
Also from warm to cold regions on smaller scale (land –
sea breezes)
Remember that there must be conservation of mass =>
return flow!
Three biggies!
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Hadley circulation
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Monsoons
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Covers entire tropics
Moves energy from equator to sub-tropics
Moves heat from ocean to land
Seasonal / regional – driven by solar heating over land
Walker circulation
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Regional across equatorial Pacific (huge region!)
Moves heat from warm western Pacific to cooler eastern
Pacific (ocean sea surface temperature)
El Nino Southern Oscillation (ENSO) is associated with
fluctuations of Walker circulation
Convergence => coming together
Convection => rising motion
Divergence => spreading apart
Subsidence => sinking motion
Hydrologic Cycle
Residence time
= Average amount of time material spends within a reservoir
= Burden / Sink ( amount in reservoir / rate of loss)
Wind-driven Ocean Circulation
Thermohaline Circulation
Driven by density variations
Very long timescale: ~ 1000 years
Climate modeling
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Demonstrate understanding of the climate
system
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Simulate current climate
Predict climate of the future
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Simulate future climate
So, how are we doing?
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GCMs do a very good job of simulating
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GCMs do less well in simulating
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Large scale behavior of the climate system
Seasonal cycle
Ocean-atmosphere coupling
Hydrologic cycle (clouds and precipitation)
Climate variability
GCMs do a poor job of simulating
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Regional climate variations
ENSO and Internal Variability
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Ocean and atmosphere are systems with
different time scales for heating
Both systems are non-linear => systems
respond in complex ways to forcing
If we couple two non-linear systems with
different response times, we can get oscillations
These oscillations are internal (not caused by
changes in external forcing) and natural
As we think about climate change, we have to
remember that the climate system has natural,
internal variability
Where to next?
Atmosphere circulation
 Ocean circulation
 Can we model this mess?
 Carbon cycle
 Earth history
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The Terrestrial Organic Carbon Cycle
Atm. CO2
760 Gt
Photosynthesis
Respiration
60
Plants
30
Consumers
0
600 Gt
FAST
decay
30
death
death
0
30
Soils and sediments
SLOW
1,600 Gt
0.05
burial
Sedimentary Rocks
10,000,000 Gt
weathering
0.05
End of last ice-age – rise of
human civilization
Modern ice-ages begin
Asteroid impact – end of dinosaurs
Cambrian explosion of life –
beginning of fossil record
Earth freezes over? – life survives
in small pockets?
Rise of atmospheric oxygen
Earliest evidence of life –
prokaryotic bacteria
Formation of earth
Onwards to Climate Forcings
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Solar activity
Faint early sun
 Snowball earth
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Earth-sun position
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Ice ages
Aerosol
Volcanism
 Asteroid impacts
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Greenhouse warming
Faint Early Sun Paradox
Sun was less luminous (less energy
reaching earth)
 But life is evident
 Life requires liquid water
 But planet was too cold for liquid water
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Conceptual framework:
Tsfc = f( S0, Albedo, Tg )
Snowball earth
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Climate models (and our simple feedback analysis)
suggest that there is an instability in our climate system
that would produce an ice-covered planet (snowball)
Instability could be triggered by a reduction in
greenhouse gas concentrations, especially coupled with
a fainter sun (about -6% in Neoproterozoic)
Earth freezes over (continents at equator) and biology
survives in a few local places
CO2 builds up from volcanism
Greenhouse effect builds up and melts ice
Lots of weathering – draws down CO2 to a new climate
equilibrium
Pleistocene Glaciations
Bars indicate “melt” starts – look at the regularity? Cause?
Eccentricity
Tilt
Precession
100,000 years
41,000 years
26,000 years
Milankovitch Cycles – based on Orbital Parameters
Lessons learned
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Current climate is not the only possible one for Earth
(indeed, glacial conditions seem to be preferred)
A change in surface temperature of about -5 °C is
associated with a massive climate shift
Global climate and CO2 appear to be intimately
intertwined
If the orbital parameter theory is right, small triggers can
produce major climate changes under some conditions
But… there are many remaining questions and enigmas
Volcanic eruption effects on climate
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Cool surface and troposphere by reflecting solar
radiation (typical effect is -1 to -2 °C)
Warm stratosphere by absorbing warm outgoing
infrared radiation (about 1 °C)
Effects last for a year or two
Climate Forcings
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Solar activity
Faint early sun
 Snowball earth
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Earth-sun position
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Ice ages
Aerosol
Volcanism
 Asteroid impacts
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Greenhouse warming
IPCC Conclusion
In the light of new evidence and taking into
account the remaining uncertainties, most
of the observed warming over the last 50
years is very likely to be due to the
increases in greenhouse gas
concentrations.
Climate stabilization – fixed CO2 level
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Need to know BOTH
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These factors determine acceptable level of CO2
This CO2 level determines emissions scenario
Critical factor is climate sensitivity
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Acceptable level of global warming
Climate sensitivity
If climate sensitivity is large => already in trouble
If climate sensitivity is small => have longer time to
solve problem
Cost is inversely proportional to solution time
Policy Response
1992 United Nations Framework
Convention on Climate Change
GOAL—”…stabilization of greenhouse gas
concentrations in the atmosphere at a level
that would prevent dangerous
anthropogenic interference with the climate
system.” (Article 2)
P.S. Our country is a signatory!
US Policy Response
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Emissions mitigation
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Business as usual
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Adaptation
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No plans
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Improved
understanding
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Static funding for a
decade
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Technology
development
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Limited and poorly
focused (freedom car)
Wow!
That was a lot of material to cover!
(but, remember, you are getting 5 credits)