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Climate Change Projections
• Wet regions will become wetter • Dry regions will become drier • Precipitation will occur less frequently • Precipitation will be more intense
Why?
Concepts
• Radiation, albedo, and greenhouse effect • Surface energy budget • Saturation and temperature • Adiabatic expansion and compression • The hydrological and energy cycle • Effects of global warming
Visible light, infrared (IR), ultraviolet (UV), X-rays, γ-rays, microwaves, and radio are all forms of electromagnetic radiation Each type has a different wavelength (λ). The shorter the wavelength, the greater the energy of individual photons Shortest to longest wavelength: γ-rays, X-rays, UV, visible, IR, microwave, radio
Sun
Earth
Sun
Earth’s Energy Budget
Earth
• Earth absorbs visible and near IR radiation from the Sun • Earth emits thermal infrared radiation back to space • Certain constituents reduce emission to space
Solar Radiation • Solar radiation flux at the average distance of Earth’s
orbit (S0) is about 1367 W m-2
(This is equivalent to 22.8 60W light bulbs every square meter)
• This solar radiation intersects with πR2 area, where R is the radius of the Earth
Solar Radiation • The total energy rate for solar radiation intersecting
Earth is S0 πR2 and global surface area of Earth is 4πR2
• The average amount of solar radiation per m2 spread out over the Earth is S0 / 4 = 342 W m-2
(This is equivalent to 5.7 60W light bulbs every square meter)
Planetary Albedo • Planetary albedo αp is the global average fraction of
solar radiation reflected back to space. • Earth’s planetary albedo is 0.31 • The global average value of reflected solar flux is
αp S0 / 4 = 107 W m-2 • The global average value of absorbed solar flux is
(1 – αp) S0 / 4 = 235 W m-2
Various Albedo Values • Ocean albedo is about 0.1 (except for sunglint) • Sandy desert albedo is about 0.25-0.35 • Forest albedo is about 0.15 • Snow/ice albedo is about 0.6-0.9 • Cloud albedo is about 0.3-0.6
Greenhouse Effect • The reduction in the amount of energy leaving the Earth
caused by clouds and greenhouse gases acts like a blanket to keep the Earth warmer
• Clouds and greenhouse gases also emit IR radiation toward the surface (324 W m-2)
• The surface absorbs this additional radiation and thus is kept warmer
Greenhouse Effect • The strongest greenhouse gas is water vapor • The next strongest greenhouse gas is CO2 • Clouds (composed of liquid water droplets and ice
crystals) have a greenhouse effect and an albedo effect • High clouds have the strongest greenhouse effect
because they are coldest
Surface Energy Budget
• Energy transfer between the surface and the atmosphere is not purely radiative
• A major component of energy transport from surface to atmosphere is via water (latent heat)
• The hydrological cycle is closely tied to the energy cycle
Energy Cycle Game
Players • Sun • Earth’s Surface • Earth’s Atmosphere • Space
Game components • White chips (solar energy) • Red chips (thermal energy)
Rules for No-Atmosphere Game
Steps for each turn A. Sun takes 4 white chips from the bank B. Sun gives 4 white chips to Surface C. Surface exchanges with the bank 4 white chips for 4 red
chips D. Surface gives half (rounding down) of red chips to
Space E. Space returns red chips to bank
Play until Surface has the same number of red chips at
the end of every turn
Questions for No-Atmosphere Game
• What does each step physically represent? • At the end of the game, how many red chips does
Surface give to Space each turn? • At the end of the game, how many red chips does
Surface have at the end of each turn?
Rules for With-Atmosphere Game
Steps for each turn A. Sun takes 4 white chips from the bank B. Sun gives 4 white chips to Surface C. Surface exchanges with the bank 4 white chips for 4 red
chips D. Surface gives half (rounding down) of red chips to
Atmosphere E. Atmosphere gives half (rounding down) of red chips
back to Surface F. Atmosphere gives the rest of red chips to Space G. Space returns red chips to bank
Rules for With-Atmosphere Game
Play until Surface has the same number of red chips at the end of every turn
Questions for With-Atmosphere Game
• What does each step physically represent? • At the end of the game, how many red chips does
Surface give to Atmosphere each turn, minus the number of red chips Atmosphere gives back?
• At the end of the game, how many red chips does Atmosphere give to Space each turn?
• At the end of the game, how many red chips does Surface have at the end of each turn?
Increase in Greenhouse Effect
• Repeat game with Atmosphere giving half of red chips rounded up back to the surface
• Surface still gives atmosphere half of red chips rounded down
Water Cycle Game
Players • Earth’s Surface • Earth’s Atmosphere
Game components • Blue chips (water)
Rules for Water Cycle Game
Before game starts Surface takes lots of blue chips from bank Steps for each turn A. Surface gives 2 blue chips to Atmosphere B. Atmosphere gives 2 blue chips to Surface
Play until bored
Questions for Water Cycle Game
• What does each step physically represent? • What is the significance of no exchanges with the bank
once the game starts?
Latent Energy Transport
• Energy is required to convert liquid water to vapor • When liquid water evaporates, the surface is cooled • Water vapor rises in the atmosphere • When water vapor condenses, the atmosphere is heated • Precipitation falls back to the surface
Energy+Water Cycle Game
Players • Sun • Earth’s Surface • Earth’s Atmosphere • Space
Game components • White chips (solar energy) • Red chips (thermal energy) • Blue chips (water)
Rules for Energy+Water Cycle Game
Steps for each turn A. Sun takes 4 white chips from the bank B. Sun gives 4 white chips to Surface C. Surface exchanges 4 white chips for 4 red chips D. Surface gives half (round down) of red chips to Atmosphere E. Surface gives an additional 2 red chips paired with 2 blue
chips to Atmosphere F. Atmosphere gives 2 blue chips (no red) back to Surface G. Atmosphere gives half (round down) of red chips to Surface H. Atmosphere gives the rest of red chips to Space I. Space returns red chips to bank
Rules for Energy+Water Cycle Game
Play until Surface has the same number of red chips at the end of every turn
Questions for Energy+Water Game
• What does each step physically represent? • What role does water play in this game? • At the end of the game, how many red chips does
Surface give to Atmosphere each turn, minus the number of red chips Atmosphere gives back?
• At the end of the game, how many red chips does Atmosphere give to Space each turn?
• At the end of the game, how many red chips does Surface have at the end of each turn?
Evaporation and Condensation
vapor
liquid
evaporation condensation
Saturation occurs when evaporation and condensation are in equilibrium
Saturation
• Saturation units are vapor pressure or specific humidity (SH) (g water per kg air)
• Relative humidity (RH) is the amount of water vapor as a percentage of saturation
• RH < 100% water evaporates • RH > 100% water condenses • RH = 100% equilibrium at saturation
Saturation and Temperature
From http://www.atmos.washington.edu/2002Q4/211/notes_water.html
Spec
ific
Hum
idity
SH
Evaporation and Condensation
vapor
liquid
evaporation condensation
Greater saturation vapor pressure at warmer temperature
Humidity and Temperature
From http://commons.wikimedia.org/wiki/Category:Snow and http://commons.wikimedia.org/wiki/Saguaro
Group Discussion Which has greater relative humidity? Which has greater specific humidity?
Humidity and Temperature
From http://commons.wikimedia.org/wiki/Category:Snow and http://commons.wikimedia.org/wiki/Saguaro
RH = 100%, SH = 3 g/kg RH = 15%, SH = 6 g/kg
Soda Can Demonstration
From http://www.atmos.washington.edu/2003Q3/101/webnotes.html
atmospheric pressure at sea level
heat to boiling
Soda Can Demonstration
From http://www.atmos.washington.edu/2003Q3/101/webnotes.html
atmospheric pressure at sea level
rapid cooling
Adiabatic Expansion
Why does temperature usually decrease with height? • When an air parcel rises, it goes to a level with less
atmospheric pressure • Since pressure is less, the air parcel expands • In order to expand, it must work to push the surrounding
air out of the way
Adiabatic Expansion
• If there is no energy input into the system (adiabatic), then the energy for the work of expansion must come from internal energy
• Internal energy is energy from the motion of molecules (temperature)
• Less internal energy means the air parcel cools down
Adiabatic Compression
• When an air parcel subsides, it goes to a level with more atmospheric pressure
• Since pressure is greater, the air parcel is compressed • Compression increases the internal energy of the air
parcel • The air parcel warms up
The Hydrological Cycle
Warm, moist air rises and cools Water vapor condenses and precipitates
Cold, dry air subsides and warms
Air is very dry (g/kg) due to precipitation loss
Air moistens from surface evaporation
The Hydrological Cycle
Warm, moist air rises and cools Water vapor condenses and precipitates
Cold, dry air subsides and warms
Air is very dry (g/kg) due to precipitation loss
Air moistens from surface evaporation
Water loss
Water gain
The Energy Cycle
How does the rising air maintain positive buoyancy so it can continue rising?
latent heat from condensation How does the subsiding air maintain negative buoyancy
so it can continue sinking? net radiative cooling (more emitted than absorbed)
The Hydrological Cycle
Warm, moist air rises and cools Water vapor condenses and precipitates
Cold, dry air subsides and warms
Air is very dry (g/kg) due to precipitation loss
Air moistens from surface evaporation Energy gain
from latent heating (“furnace”)
Energy loss from radiative cooling (“radiator fin”)
Water and Energy Balance
Approximately… precipitation = surface evaporation latent heating = atmos. radiative cooling Implication… the magnitude of radiative cooling controls the
magnitude of precipitation
Global Warming and Saturation Sp
ecifi
c H
umid
ity
SH
As temperature warms, saturation specific humidity strongly increases More water can evaporate into the atmosphere
Global Warming and Saturation
• More evaporation from dry regions means dry regions get drier
• More water vapor in the atmosphere means more condensation and precipitation in wet regions
Saturation and Radiative Cooling Sp
ecifi
c H
umid
ity
SH
As temperature warms, net radiative cooling of the lower atmosphere weakly increases
Rad
iativ
e C
oolin
g (W
m-2
)
Global Warming Effects
Strong increase in net radiative cooling
Weak increase in net radiative cooling
Weak increase in precipitation
Middle atmosphere
Lower atmosphere
Strong increase in water vapor
Water and Energy Balance
Approximately… latent heating = atmospheric radiative cooling Implication… a small increase in radiative cooling means there can
only be a small increase in precipitation
Global Warming and Precipitation
• Weak increase in global average precipitation • Strong increase in water vapor available to be rained out Implication… Precipitation events become stronger but less frequent
Surface Energy Budget
• Energy transfer between the surface and the atmosphere is not purely radiative
• Net (up – down) IR flux is 66 W m-2 • Evaporative heat flux is 78 W m-2
• Absorbed solar flux is 168 W m-2
Primary surface energy balance at many locations: solar heating evaporative cooling
Surface Energy Budget
• Energy transfer between the surface and the atmosphere is not purely radiative
• Net (up – down) IR flux is 66 W m-2 • Evaporative heat flux is 78 W m-2
• Absorbed solar flux is 168 W m-2
Primary surface energy balance at many locations: solar heating evaporative cooling What might happen if surface solar heating is weakened?
Regional Anthropogenic Aerosol
From http://www.sciencemuseum.org.uk/antenna/sootyclouds/ and http://scrippsnews.ucsd.edu/Releases/?releaseID=860
Solar Heating and Precipitation
Large energy gain from latent heating Large energy
loss from radiative cooling
Large energy loss from evaporative cooling
Large energy gain from solar heating