Lecture 8 Flashcards
Blackbody
a hypothetical object that absorbs all light with no reflection, and emits only a range of energy dependent on temperature.
An opaque object that emits thermal radiation
Example of a black body
The sun at 5800K
Earths UV-light regions
UV-a –> long wave UV 315-400nm, low energy. Near visible light. 5% is absorbed by ozone
UV-b –> middle, 280-315nm. 95% is absorbed by ozone
UV-c –> short wave UV 100-280nm, high energy. 100% absorbed by ozone
Radiation balance
energy must be returned to space to maintain heat balance
1) some solar radiation is reflected by surface, but some absorbed & re-emitted to space
2) some gases (greenhouse) absorb strongly in IR
3) IR is re-emitted in all directions, heating both surface and air
Earths energy budget
93% of energy heats oceans, 3% of energy heats land & atmosphere, 4% melts ice
absorbance spectrum of O
O2, O3, O absorbed in UV 50-440nm
absorbance spectrum of H2O
Very little absorbance is visible light. Primary absorber in IR region
Radiative forcing
Phenomena that perturb the energy balance. The difference between the solar radiation received by earth & IR radiated back to space
Cooling is negative force
Warming is positive force
What is radiative force affected by
changes in insolation, concentration of greenhouse gases, aerosol size & prevalence
What are two ways to measure past temperatures?
Proxy Based analysis –> Natural imprints (tree rings, ice cores, lake sediment, corals)
Instrumental methods
In atmospheric window where does H2O absorb
IR region strongly 2.5-3nm, 5-8 and >14
In atmospheric window where does CO2 absorb
In water vapour window 12-16.3
Why cant oceans remove all of the CO2?
1) CO2 is made faster than it is absorbed
2) Increase in temperature of oceans increases degasification
Radiative forcing (RF) components
(there are 3)
1) the wavelength at which gas is absorbed
2) strength of absorption per molecule
3) present atmospheric concentration
Global warming potential (GWP)
a radio defined based on the product of the instantaneous RF value & residence time for species over same CO2 value
