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3. Global Energy Balance.docx

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Environmental Science
Luc Bernier

ENVIR SCI 1A03 Global Energy Balance Role of the Sun • Radiation: energy emitted to the surface • Core of the sun – where nuclear fusion occurs and where energy is from • Energy travels from the sun to the atmosphere • Solar luminosity of the sun was weaker than present time o Without taking into consideration radiation from Earth, the Earth was cooler then than now • Earth’s position in the Sola System contributes to global temperature Link Between Temperature and Radiation 4 • Stefan-Boltzmann equation: E = θT o E = intensity of radiation (W/m )2 o θ = Stefan-Boltzmann constant = 5.67 x 10 W/m K8 2 4 o T = temperature in Kelvin • What is a Blackbody? o Body that is perfectly efficient at emitting radiation according to the Stefan-Boltzmann equation o Greybodies only emit a fraction of max radiation  I = εθT4  ε = emissivity factor (=1 for blackbodies) o Almost all celestial bodies are blackbodies. • Wein’s Law: λ = 2897/T o λ = wavelength of max radiation intensity (μm) max o T = temperature (K) o Higher temperature = shorter wavelength (carries more energy) What is Insolation? • Incoming solar radiation • Depends on the angle of solar radiation • Equator: equal amount of insolation, focused on a smaller area • Poles: insolation spreads over a large area • Results in variation of energy spread • Interference of the atmosphere reflects radiation and only a fraction is absorbed by and reaches the Earth o Radiation in blue wavelength is usually reflected resulting in blue sky • What is Albedo? o Proportion of incoming radiation vs. what is reflected back to space o Most of radiation is absorbed by concrete  resulting in urban heat islands (cities) What is net radiation? • Incoming radiation – outgoing radiation • Deficit = surplus, for net radiation = 0. (Just as much energy influx as out flux) • This is very rare • Surplus is decreasing as latitude increases o The same energy is distributed over a wider area thus there is less solar energy at larger areas What is the Pole ward Heat Transport? • Surplus energy moves toward poles (deficit regions) • This surplus energy is transported through different mechanisms - - warm moist air, warm oceans (ocean currents), cyclones, major storm systems • Surplus at the equator and at the poles there is a zone of deficit • Energ
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