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Earth’s Energy Balance

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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Earth’s Energy Balance

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  1. Earth’s Energy Balance

  2. 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

  3. The Sun’s Rays Don’t Heat Earth Evenly Image source: earthobservatory.NASA.gov

  4. The Earth is not Warmed Evenly • Areas near the equator receive more sunlight • Sunlight received near poles is not as strong

  5. 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

  6. Your Latitude determines your Solar Energy Image source: earthobservatory.NASA.gov

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

  8. 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

  9. 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”)

  10. Incoming solar radiation is reflected Image source: earthobservatory.NASA.gov

  11. Incoming solar radiation is reflected Or absorbed Image source: NASA’s Earth Observatory

  12. Solar radiation absorbed by earth is convected, evaporated and re-radiated back to atmosphere Image source: NASA’s Earth Observatory

  13. The Greenhouse Effect causes some of earth’s re-radiated energy to remain close to the surface. Image source: NASA’s Earth Observatory

  14. Energy in atmosphere (from incoming solar radiation and earth’s re-radiation) is emitted back out to space. Image source: NASA’s Earth Observatory

  15. Reflected solar radiation + outgoing heat radiation = incoming solar radiation A balance is maintained! Image source: NASA’s Earth Observatory

  16. 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

  17. 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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