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Earth’s Energy Balance. We are Sun Powered. Earth is warmed by the sun Exception: geothermal energy The Sun adds 342 Watts of energy per square meter of earth every year Energy from the sun radiates through space as electromagnetic waves. Image source: science. NASA.gov.

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Presentation Transcript
we are sun powered
We are Sun Powered
  • Earth is warmed by the sun
    • Exception: geothermal energy
  • The Sun adds 342 Watts of energy per square meter of earth every year
  • Energy from the sun radiates through space as electromagnetic waves

Image source: science. NASA.gov

the sun s rays don t heat earth evenly
The Sun’s Rays Don’t Heat Earth Evenly

Image source: earthobservatory.NASA.gov

the earth is not warmed evenly
The Earth is not Warmed Evenly
  • Areas near the equator receive more sunlight
  • Sunlight received near poles is not as strong
tilt of earth causes seasons
Tilt of Earth Causes Seasons
  • Uneven heating of Earth is why we have seasons
  • Always warm at equator because sun is nearly directly overhead
  • Big variation in temps at poles because angle of sunlight varies greatly over the year
  • These variations in heating drive Earth’s climate and weather

Image source: www.windows.ucar.edu

your latitude determines your solar energy
Your Latitude determines your Solar Energy

Image source: earthobservatory.NASA.gov

overheating
Overheating?

If Earth is receiving so much solar energy, why aren’t we heating up like an oven?

there s a balance
There’s a Balance!
  • Some solar radiation is reflected/absorbed by atmosphere before it reaches Earth.
  • Solar radiation (short wavelength) warms the earth. Earth radiates some of that energy (long wavelength) back towards space.
  • Incoming energy must equal outgoing energy to keep things in balance.

Image source: esrl.NOAA.gov

of course it s a bit more complex
Of Course, It’s a Bit More Complex…
  • If the radiation emitted by Earth just escaped back into space, Earth’s surface would be very, very COLD!
  • The atmosphere is absorbing some of that radiation and keeping Earth comfortably warm. This is the Greenhouse Effect(see “Greenhouse Effect.ppt”)
slide10

Incoming solar radiation is reflected

Image source: earthobservatory.NASA.gov

slide11

Incoming solar radiation is reflected

Or absorbed

Image source: NASA’s Earth Observatory

slide12

Solar radiation absorbed by earth is convected, evaporated and re-radiated back to atmosphere

Image source: NASA’s Earth Observatory

slide13

The Greenhouse Effect causes some of earth’s re-radiated energy to remain close to the surface.

Image source: NASA’s Earth Observatory

slide14

Energy in atmosphere (from incoming solar radiation and earth’s re-radiation) is emitted back out to space.

Image source: NASA’s Earth Observatory

slide15

Reflected solar radiation + outgoing heat radiation

= incoming solar radiation

A balance is maintained!

Image source: NASA’s Earth Observatory

natural climate forcings changes to the balance
Natural Climate ForcingsChanges to the Balance
  • Changes in the Sun’s brightness
  • Variations in Earth’s orbit and tilt
    • Milankovitch cycles and ice ages
  • Large volcanic eruptions
    • Add particles to atmosphere
manmade climate forcings changes to the balance
Manmade Climate ForcingsChanges to the Balance
  • Particle pollution
    • Changes how radiation reflected/absorbed
  • Changing surface of earth (deforestation)
    • Changes how radiation reflected/absorbed
  • Adding greenhouse gases
    • Changes how heat is re-radiated to space
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