L2 - Radiation and the GHG effect Flashcards
What are the main greenhouse gases?
Water vapor, carbon dioxide, ozone, methane, CFCs, HFCs, N2O, SF6
What would Earth’s surface temperature be without greenhouse gases?
-18 deg C
What is Earth’s surface temperature with greenhouse gases?
15 deg C
What is the mean temperature increase due to the greenhouse effect?
33 deg C
What type of radiation does the Sun emit?
high-temperature sources (shortwave radiation)
How does solar radiation interact with Earth’s atmosphere?
Some is absorbed by clouds and gases, most passes through and warms the surface, some is reflected back into space
What happens to infrared radiation emitted by Earth?
Some is absorbed and re-emitted by greenhouse gases, warming the surface and atmosphere
What is the equation for electromagnetic radiation?
vλ = c
What does each symbol in vλ = c represent?
v = frequency, λ = wavelength, c = speed of light
Which types of radiation carry the most energy per wave?
X-rays
What objects emit radiation?
All objects with a temperature greater than 0 K
What are the two key radiation laws?
Stefan-Boltzmann Law and Wien’s Law
What does Stefan-Boltzmann Law state?
Total energy emitted by a black body relates to temperature: I(T) = σT⁴
What does Wien’s Law describe?
The peak wavelength of emission depends on temperature: λ_max T = 2.897 x 10⁶
How does wavelength change with temperature?
Higher temperature → shorter wavelengths; Lower temperature → longer wavelengths
What is Earth’s equilibrium temperature without greenhouse gases?
255K (-18°C)
What is Earth’s observed surface temperature?
288K (15°C)
What is Earth’s albedo?
30% of incoming solar radiation is reflected
How much solar radiation is absorbed by land and water?
51%
What percentage of absorbed radiation is re-emitted as infrared radiation?
15%
What is the role of greenhouse gases in radiation balance?
They trap longwave radiation, leading to atmospheric warming
What is the difference between absorption and emission?
Absorption: A molecule absorbs energy and moves to a higher state
Emission: A molecule drops to a lower energy state and emits a photon
How do different molecules absorb radiation?
They absorb radiation at specific wavelengths corresponding to energy level differences
What is the equation for photon energy?
E = hf = h/λ
What is the greenhouse effect?
GHG absorb and re-emit infrared radiation, warming Earth’s surface
do warmer or colder objects emit more intensely
warmer
how do warmer objects emit energy compared to colder objects
- warmer = high proportion of energy emitted at shorter wavelength
- colder = longer wavelength
what is a black body
absorbs all radiation falling on it and re-emits it as a function of its surface temp
where is the suns energy concentrated in a narrow wavelength region
0.4 and 0.7 microns (visible part of spectrum)
how do all bodies radiate energy
as electro-magnetic radiation
The Stefan-Boltzmann law relates how the total energy emitted by a black body relates to the temperature by I(T) = σT4 , what does this equation stand for?
I = energy per unit area emitted per second (watts m-2)
T = blackbody temp (K)
σ = Stefan-Boltzmann constant (5.67 x 10-8 m-2 K-4)
what is the difference between solar and terrestrial radiation
solar= 5900K, short wave
terrestrial = 288K , long wave
what is radiation the primary energy source for
atmospheric and ocean circulation and for all life on Earth
what is the albedo of clouds
- very dark = albedo close to 0%
- very light =
what are the GHG effects of solar radiation?
- some solar radiation absorbed by Earth’s surface and atmosphere
- Earth and atmosphere emit infrared radiation
- GHG absorb some of this infrared radiation in all directions
- Earth absorbs downward directed infrared radiation
- Result = warmer surface temperature = 288 K rather than 255K
