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
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)
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
• 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
• 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