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Understanding Earth's Emissivity and Temperature: Blackbody Radiation Calculations

This article explores the concept of Earth as a blackbody, detailing calculations of power emitted by oceans and the planet itself. We start by calculating the power radiated from a square kilometer of ocean surface at 100°C with an emissivity of 0.65. Next, we derive Earth's radiated power assuming it behaves as a perfect blackbody and as a blackbody with an emissivity of 0.62. Given the average incident power of 1.23 x 10^17 watts, we determine Earth's equilibrium temperature and discuss its measured average temperature of 288 K, exploring the reasons behind this discrepancy.

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Understanding Earth's Emissivity and Temperature: Blackbody Radiation Calculations

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Presentation Transcript

  1. Earth as a blackbody

  2. The Earth (and other planets) also act as a blackbody, usually with emissivity.

  3. Calculate the power emitted by a square kilometer of ocean surface at 100C if its emissivity is 0.65.

  4. 2. Calculate the power radiated by the Earth if it is taken to be… a) a perfect blackbody b) a blackbody, with emissivity of 0.62

  5. If we say the average power, incident on the Earth, is 1.23 x 1017 watts, and the emissivity is 1 (power in=power out), what would be the equilibrium temperature of the Earth? (Radius of Earth:6.38 x 106m)

  6. So…255K, that’s -18° C. Too cold. The average equilibrium temperature of Earth is actually measured at 288 K. Calculate the emissivity of the Earth. • What causes this?

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