Conversations with the Earth

Tom Burbinetburbine@framingham.edu

Albedo• Albedo is the reflectivity of the surface

• Albedo goes from 0 to 1

• High albedo – reflective

• Low albedo - absorbing

Planetary Energy Balance Equation

• Exercise 5

• 1) What does energy balance mean?

• 2) If we want to determine the energy emitted by the Earth, what do we have to assume about the Earth?

• 3) What is the formula for the energy flux from a blackbody?

• 4) What must we multiply this equation by if we want to determine the energy emitted by the whole Earth?

• Area of sphere = 4R2

• Area of Earth = 4Rearth2

• 5) What is the equation for the energy emitted by the Earth?

• 6) The energy absorbed by the Earth’s surface from the Sun will equal what minus what?

• 7) What is the Solar Flux on the Earth?

• S = Solar Flux = 1366 W/m2

• 8) To determine energy intercepted by Earth from Sun, you need to multiply the Solar Flux by what?

• Area of Earth that intercepts Sun’s rays = R2

• 9) What do you have to multiply the Solar flux by to determine how much energy is reflected?

• Area of Earth that intercepts Sun’s rays = R2

• Albedo = A

• 10) So the energy intercepted minus the energy reflected equals what? This is the energy absorbed by the Earth.

• 11) Equate the energy emitted by the Earth and the energy absorbed by the Earth to determine the energy balance equation

T4 =(S/4)(1-A)

• 12) From the Planetary Energy Balance Formula, calculate what the temperature is equal to?

• T = [(S/4)(1-A)]1/4

• 13) Using the Planetary Enjergy Balance Equation, what should be the temperature of the Earth?

• S = 1366 W/m2

• A = 0.30 = 5.67 x 10-8 W/(m2 K4)

• 14) The mean surface temperature of the Earth is 288 K, why is the calculated temperature lower than the real temperature?

• http://www.hulu.com/watch/23343/scientific-american-frontiers-hot-planet-%E2%80%93-cold-comfort

Any Questions?