Planetary Energy Balance PDF

Planetary Energy Balance: IN = OUT We equate incoming radiation with outgoing radiation. Assumptions: Earth behaves like a blackbody Earth’s temperature is not changing Planetary Energy Balance: IN AEarth = 0.3 Earth projected against the sun’s rays is a circle area of circle textbook Figure 3...

Planetary Energy Balance: IN = OUT We equate incoming radiation with outgoing radiation. Assumptions: Earth behaves like a blackbody Earth’s temperature is not changing Planetary Energy Balance: IN AEarth = 0.3 Earth projected against the sun’s rays is a circle area of circle textbook Figure 3 -1 Planetary Energy Balance: OUT Energyemitted = area of sphere 4π R σT 2 Earth 4 e StefanBoltzmann The energy flux radiated by the Earth equals its surface area times the flux per unit of area. Planetary Energy Balance Energyabsorbed = Energyintercepted – Energyreflected In Energyabsorbed = = Energyemitted = 2 2 π REarth S − π REarth SA πR 2 Earth 4π R ( S 1− A σT 2 Earth ) 4 e Out see textbook p. 44 and 45 for details πR ( ) S (1− A ) S 1− A = 4π R σ Te 2 Radiating Temperature 2 Effective Earth Earth Te = 4 e 4σ Variable Symbol Value Solar flux S 1366 W/m2 Albedo A 0.3 Stefan-Boltzmann constant s 5.67E-08 W/m2/K4 πR ( ) S (1− A ) S 1− A = 4π R σ Te 2 Radiating Temperature 2 Effective Earth Earth Te = 4 e 4σ This is the temperature that a true blackbody would need to radiate the same amount of energy that Earth radiates. IR UV λmax Sun λmax Earth visible light We use the 'one-layer model' of the atmosphere to illustrate the greenhouse effect textbook Figure 3 -2 textbook Figure 3 -2 textbook Figure 3 -2 textbook Figure 3 -2 textbook Figure 3 -2 textbook Figure 3 -2 textbook Figure 3 -2 textbook Figure 3 -2 Balancing incoming and outgoing energy for both the atmosphere and the Earth's surface, a simple result falls out: 1 Ts = 2 Te 4 Temperature at the Earth’s surface (Ts) is higher by a factor of ~ 1.2 than it would be in the absence of the one-layer atmosphere. A gas that can absorb or emit infrared energy. Two possible ways: 1. They can change their rotation rate (12 μm band) A gas that can absorb or emit infrared energy. Two possible ways: leads to absorption in the H2O rotation band 1. They can change their rotation rate (12 μm band) A gas that can absorb or emit infrared energy Two possible ways: 2. They can change their vibration rate A gas that can absorb or emit infrared energy Two possible ways: leads to absorption in the 15µm CO2 band 2. They can change their vibration rate infrared energy does not interact with symmetric molecules. because there is no separation of negative and positive electrical charge The major gases are not greenhouse gases The gases that cause the greenhouse effect are only minor constituents 424 May 2023 1.92 May 2023 The gases that cause the greenhouse effect are only minor constituents % of IR radiation absorbed during vertical passage through the atmosphere textbook Figure 3-13 nearly complete absorption of IR radiation longer than 13 µm by CO2 and H2O IR UV λmax Sun λmax Earth visible light IR UV λmax Sun λmax Earth visible light IN (100 - 30) = OUT (70) Planetary energy budget is out of balance. Earth is absorbing more energy from the Sun than it is radiating back to space due to the increasing greenhouse gas concentrations. The imbalance is ~ 0.6 W m-2 Source: Intergovernmental Panel on Climate Change (IPCC, AR5) 2013 The imbalance is ~ 0.6 W m-2 0.79 W m-2 Source: Intergovernmental Panel on Climate Change (IPCC, AR5) 2013 2021