lecture 2 Flashcards
Why do the sun and earth have different spectral properties? wavelength reflects intensity of energy flux
No atmosphere, straight exchange
Values of energy in and out in Wm-2
Planet emits longer wavelength radiation
Temperature of a radiating body definition
is a function of energy out (emissivity) and σ, the Stefan-Bolzmann contstant (5.67 x 10-8), and albedo
Temperature of earth with no atmosphere
-18oC
Abundant atmospheric gases (not GHGs)
Nitrogen, Oxygen and water vapour
GHG molecules, natural gases
Trace atmospheric gases
Co2, methane
Nitrous oxide, ozone
Unnatural gases
Halocarbons
Sulfa Hexafluoride Sf6
= human made and most potent and long lasting of the GHGs
Absorption capacity of atmosphere depends on
amount of each type of molecule present
absorption spectrum of each type of molecule
In order for the greenhouse effect to work what must be present in the atmosphere?
Greenhouse gases
Changing the atmospheric composition of greenhouse gases such as Co2 does what to the atmosphere?
Alters the atmosphere’s capacity to absorb and re-radiate energy
To balance the input and output of energy what is required?
heating of atmosphere and
Earth surface – a planet with atmosphere is
warmer than it would otherwise be
What affects energy pathways?
Albedo
Why is energy exchange usually measured at the top of the troposphere?
GHGs are active below tropopause and therefore lose energy at the top of the troposphere
What is the lapse rate of the troposphere?
warms and becomes denser towards the surface
The more molecules of GHG added, the more what?
interception and re-radiation
What is currently resultant of the ongoing process of adding GHGs and what does this mean?
Disequilibrium - heat loss from the upper troposphere is not keeping up with heat gain via increased GHGs
What is a net radiation?
the
balance between the incoming and outgoing radiation for the
planet—measured at the tropopause
Net positive at the equator and negative at the poles
What can drive a change in net radiation, temporarily disturbing the balance? and what results from this?
A perturbation (change in GHG concentration Causes temperature change
What is radiative forcing?
Change in net radiation driving a temperature change - not a always change in radiation e.g incoming solar, but a change that affects net radiation
What is a perturbation? And examples
Change in net radiation leads to a temporary energy imbalance 1. Less solar energy in (e.g change in solar constant ) 2. Overall reduction of energy in system 3. temperature decreases 4. emissions decrease to reach new balance = negative radiative forcing
What are the preindustrial, 2x and current levels of Co2
280ppm, 400ppm, 560ppm
For a temporary decrease in radiation out ( more absorbing in troposphere) what type of radiative forcing?
Positive:
temperature increases overtime as a result
Examples of positive radiative forcing? (in order)
Co2 increase, methane halocarbons increase, ozone increase, water vapour
Examples of negative radiative forcing
Cloud albedo effect, land use
If warming happened instantaneously, using the average value
of Earth’s emissivity, what forcing value causes a temperature rise?
a positive forcing of 3.75 W m-2 (that of
2xCO2) should result in a 1°K* rise in temperature
Oceans have what heat capacity?
High heat capacity
Temperature increase since GHGs began to rise?
0.5oC
Emergy imbalance due to GHG increasing to 400 ppm is..?
1.0 wm-2
Planet’s sensitivity =
How much the earth finally warms for 2xCo2
Positive feedbacks raise the estimates of 2xCo2 temperature increase to
2.1 - 4.4 oC
Climate models attempt to do what?
Deal with all the critical forcings and feedbacks and take into account earth’s varied surface and interactions between land, ocean and atmosphere
Climate sensitivity
The net response of the climate to a 2xCo2 forcing is 2.1-4.4 oC Response of the earth system to the overall radiative forcing
What temperature rise is aimed to limiting
2oC
