earth’s energy balance. we are sun powered earth is warmed by the sun –exception: geothermal...
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Earth’s Energy Balance
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We are Sun PoweredWe 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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The Sun’s Rays Don’t Heat Earth The Sun’s Rays Don’t Heat Earth EvenlyEvenly
Image source: earthobservatory.NASA.gov
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The Earth is not Warmed EvenlyThe Earth is not Warmed Evenly
• Areas near the equator receive more sunlight
• Sunlight received near poles is not as strong
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Tilt of Earth Causes SeasonsTilt 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
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Your Latitude determines your Your Latitude determines your Solar EnergySolar Energy
Image source: earthobservatory.NASA.gov
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Overheating?Overheating?
If Earth is receiving so much solar energy, why aren’t we heating up like an oven?
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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
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Of Course, It’s a Bit More Of Course, It’s a Bit More Complex…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”)
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Image source: earthobservatory.NASA.gov
Incoming solar radiation is reflected
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Image source: NASA’s Earth Observatory
Incoming solar radiation is reflected
Or absorbed
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Image source: NASA’s Earth Observatory
Solar radiation absorbed by earth is convected, evaporated and re-radiated back to atmosphere
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Image source: NASA’s Earth Observatory
The Greenhouse Effect causes some of earth’s re-radiated energy to remain close to the surface.
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Image source: NASA’s Earth Observatory
Energy in atmosphere (from incoming solar radiation and earth’s re-radiation) is emitted back out to
space.
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Image source: NASA’s Earth Observatory
Reflected solar radiation + outgoing heat radiation
= incoming solar radiation
A balance is maintained!
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Natural Climate ForcingsNatural Climate ForcingsChanges to the BalanceChanges 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
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Manmade Climate ForcingsManmade Climate ForcingsChanges to the BalanceChanges 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