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Lecture 5

# ENVIRSC 1A03 Lecture Notes - Lecture 5: Solar Irradiance, Longwave, Boltzmann Constant

Department
Environmental Science
Course Code
ENVIRSC 1A03
Professor
Luc Bernier
Lecture
5

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GLOBAL ENERGY BALANCE
Role of the Sun
- we receive a fraction of the Sun's energy
- provides solar energy (heats up the earth + can be harnessed for other purposes)
Young Faint Sun Paradox
- early on in the sun's life, we only received 70% of the energy from the sun as we receive today
- the sun was much weaker early on
- Earth's temperature was cooler 4.6 billion years ago
- solar luminosity has increased over time
- the Earth was colder back then because of the low concentrations of radiation capturing gases
in the atmosphere (greenhouse gases)
How Does Earth's Position influence the Balance
- what would be Earth's temperature if it had the same distance from the Sun as Mercury?
WARMER
- Neptune? COLDER
The Link between Temperature and Radiation
1. Stefan-Boltzmann equation --> E = oT^4
E = intensity of radiation emitted
= Stefan =Boltzmann Constant (5.67x10^-8 W x m^-2 x K^-4)
T = surface temapature (K)
Blackbody
- Body that is perfectly efficient at emitting radiation
- for gray bodies, Stefan-Boltzmann equation becomes: I = EoT^4
- E = emissivity factor ( =1 for black bodies)
- most solids and liquids are actually graybodies
- If the temperature of the sun doubled, the impact on the radiation emitted would increase by
16X
2. Wein's Law: Y(lambda) = 2897/T
- lambda 0max = wavelength of max radiation intensity (micrometer)
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