Earth s energy balance
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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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Earth’s Energy Balance

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Earth s energy balance

Earth’s Energy Balance


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”)


Earth s energy balance

Incoming solar radiation is reflected

Image source: earthobservatory.NASA.gov


Earth s energy balance

Incoming solar radiation is reflected

Or absorbed

Image source: NASA’s Earth Observatory


Earth s energy balance

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

Image source: NASA’s Earth Observatory


Earth s energy balance

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

Image source: NASA’s Earth Observatory


Earth s energy balance

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

Image source: NASA’s Earth Observatory


Earth s energy balance

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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