Transcript Climate Change - science-b

Advanced Placement Conference
Augusta, ME
October 30, 2009
Solar Energy Budget
 Evidence of Past Climate
 Assessment of Current Climate
 Climate Projections
 Effects of Climate Change
 Current U.S. Legislative Action
 Making Climate Change Personal
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Incoming Shortwave
Outgoing Long wave
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Total solar irradiance is maximum power (watts or j/s)
that the sun can deliver to a surface perpendicular to the
path of light
Areas near the equator at noon come close to this total
Both latitude and time of day affect the irradiance
received by a particular area
On the equinox:
◦ Tropics ~
~ 90%
◦ Mid-Latitudes
~ 70%
◦ Arctic and Antarctic ~ 40%
◦ Overall
~ 25%
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Reflected Solar Energy
Net Energy Gain/Loss
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The net heating imbalance drives powerful
atmospheric and oceanic circulations
This driving force is called an “engine” because it
converts energy into motion
The effects of these imbalances and circulations
are what causes the climate of a particular
location
Evaporation, convection precipitation, winds, and
oceanic currents are all parts of this climate
engine
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Exact values for earth energy flows are
unknown and a subject of intense research
 Different Estimates exist and all estimates
have some uncertainty
 Estimates come from:
◦ Satellite observations
◦ Ground and sea-based observations
◦ Numerical climate models
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The climate engine moves heat vertically
through the atmosphere and into space as
well as along the surface
The sum of the incoming energy and
outgoing energy flow determines the
temperature of the earth
◦ Ei = Eo temperature is stable
◦ Ei > Eo earth’s temperature increases
◦ Ei < Eo earth’s temperature decreases
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Absorbed incoming solar energy (shortwave Ei)
increases the temperature of the molecules that
absorb the energy
These molecules in turn, radiate energy as heat
(long wave Eo)
The amount of energy radiated is proportional to T4
If temperature doubles:
◦ E = T4 = 24 = 16 times amount of energy
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Long wave Radiation
Shortwave radiation
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The earth’s surface and atmosphere absorb
71% of incoming solar radiation
 The atmosphere absorbs 23%, but radiates
59% of the solar radiation
 The surface absorbs 48%, but radiates only
12% of the solar radiation
 How does this reshuffling of heat energy
happen?
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Evaporation / Condensation / Freezing
◦ About 25% of energy loss / gain
◦ Latent heat
◦ Principle driver of atmospheric heat engine
 Conduction / Convection
◦ The fallacy of “Hot Air Rises”
 Radiation
◦ Infrared (λ = ~12.5 µm, ƒ = ~24 THz)
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~
59% of the earth’s energy is radiated
from the atmosphere
 23% comes directly from the sun
 25% comes from evaporation /
condensation processes
 5% comes from conduction / convection
 Where does the other 6% come from???
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Certain molecules within the atmosphere
absorb some of the radiation emitted by the
surface. This raises their temperature
◦ Asymmetry – mass – bond strength
 Once the energy is absorbed, it is re-radiated
in all directions, some of it returns to the
surface
 This return of heat energy to the surface,
increases its temperature by ~ 15oC
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Radiation energy increases as T4
As the surface warms up, so does the atmosphere
which increases the rate of transfer from bottom
of atmosphere to the top where it eventually
escapes
When top of atmosphere radiation equals
incoming solar radiation (79%), the earth’s energy
budget is balanced and the temperature remains
stable
What could de-stabilize this balance?
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Volcano Forcings
Anthropogenic Forcings
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Water vapor is strong absorber of infrared
radiation, but not at all frequencies
Infrared radiation at particular frequencies is
“invisible” to water vapor.
These are the water vapor windows and radiation
emitted at these frequencies escapes freely into
space (Most important is the 10µ m window)
Unless a different atmospheric molecule can
absorb these radiations and partially “close” the
water-vapor window
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output changes – sunspots
 Orbital / tilt changes of the earth
 Continental drift
 Vegetative changes
 Sun
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 Heat
capacity of the oceans
◦1.3 x 109 km3
 Temperature
 Effect
– Radiation balance (T4)
of clouds????
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Difficult to measure but appears to be about
0.8 Watt/m2 (average = 240 Watt/m2
 Global average surface temperature
(GAST) has risen between 0.6 – 0.9o C in
the last century
 It will likely rise at least another 0.6o C, due
to the current imbalance
 What if the imbalance gets larger????
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Instrumental Data
◦ Measurements
◦ Historical records
Proxy Data
◦ Use of O16 – O18 ratio
◦ Ice cores
◦ Tree Rings (high elevations)
◦ Lake and ocean sediments (pollen, plankton,
and dust)
◦ Coral growth bands
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Change in climate temperature – some cooler,
some warmer
Increased frequency of extreme weather
events
Vegetation shifts
◦ e.g. Great Plains become forested
◦ Animal shifts follow
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Human health negatively affected
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C-3 Plants (Wheat, Rice, Soybean) respond
readily to increased CO2 concentrations (lab
results)
C-4 plants (Corn, Sorghum, Sugarcane, Millet)
do not respond to increase in CO2
concentrations (lab results)
Stomata open less frequently thus conserving
water loss
Higher temperatures lead to
photorespiration decreasing photosynthetic
yield
 Changes in rainfall (amounts and patterns)
affect natural flora and traditional
agricultural crops
 Greater frequency of extreme weather
events will affect plants, but the extent is
unknown
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Demand for water is expected to rise
◦ Water resources are already dwindling
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Increase in soil temperature
◦ Drier soils – less root development
 Affect on nitrogen fixation
 Affect on soil erosion
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More fertilizers needed especially in newly
marginal areas
◦ Mid-latitudes
◦ High Latitudes
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More Energy Used by agriculture
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Probably the greatest impact of Climate
Change
Food and Water shortage
◦ Estimate 17% drop in food with 1o C temperature
change
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Poor sanitation
◦ Flooding overwhelming sewage treatment
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Greater pathogen spread
◦ Tropical diseases: malaria and dengue fever
◦ US 1300 cases, 8 deaths (2002)
◦ Worldwide 350 000 000 cases: one million deaths
that’s 2 deaths per minute
Poor will be hardest hit
 Most dependent on natural
resources
 Less Availability of medical care
 Less capable of mitigating affects
 Least responsible for climate
change
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Paleocene – Eocene thermal Maximum
(PETM)
◦ 6o in 20,000 years
◦ 2 short 1000 yr pulses - clathrates
 Non-Linear CO2 – Temperature relationship
◦ Positive Feedback Loops
◦ Negative Feedback Loops
 Something Else?????
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