2 - The Earth's energy budget and the greenhouse effect Flashcards
What are three different examples of interactions of radiaition with matter?
Transmission – this means no interaction
Scattering – this means radiation changes direction due to interaction with matter but does not change wavelength or energy
Absorption – transforms radiation into heat
Describe three examples of scattering of solar radiation in the atmosphere.
Gas molecules - Rayleigh scattering - wavelength dependence causes blue skies
Clouds - ice crystals/water droplets(5-10 micrometers in radius) - reflect 20% of incoming solar radiation(dominating factor in planetary albedo)
Aerosol particles - air suspended particles(<1 micrometers in radius - crucial in cloud formation process
Describe absorption within the atmosphere.
It is strongly dependent on atmospheric composition and wavelength.
UV radiation is mainly blocked by the ozone.
Visible light is only absorbed a little.
Infrared is blocked in some areas.
Describe the greenhouse effect.
The infrared layer is the absorbing layer of the atmosphere - it is transparent for solar radiation(it allows SW radiation in) whilst being a black body for terrestrial radiation(it absorbs LW radiaiton and keeps it in the atmosphere).
Therefore, the surface receives solar radiation + the back radiation from the absorbing layer.
The Earth absorbs 255K at the surface but has an average temperature of 288K, due to the multiple IR absorbing layers in the atmosphere, which each increase the Earth’s equilibrium surface temperature by around 20%.
Thus, the atmospheric GH effect increases surface temps by 33K.
What is radiative forcing?
The imbalance between outgoing and incoming radiation - it is calculated from externally imposed perturbation in the Earth’s energy budget
What are the respective figures for total anthropogenic and total atmospheric GH forcing?
Total anthropogenic = 2.3 W/m(sq)
Total atmospheric = 150 W/m(sq)
What is a feedback loop?
A mechanism that amplifies or weakens a signal in the climate system
Name some examples of feedback loops in the climate system.
Ice albedo effect is a positive feedback loop because warmer climate → less ice and snow coverage → less reflection of solar radiation → more absorption → enhanced warming
Water vapour feedback is a positive feedback loop because warmer climate → increased saturation vapour pressure → increased water vapour concentrations → enhanced warming
Thermostat effect is a negative feedback loop because warmer climate → more evaporation/water vapour/clouds → more reflection of solar radiation → cooling
What is a temperature response?
It is a change in temperature after reaching new equilibrium, including all feedbacks, after applying a forcing - it is proportional to the initial forcing
e.g. doubling of pre-industrial CO2(280 → 560 ppm) causes warming by 1.5 - 4.5K(AR5 IPCC 2013)
What is the radiative forcing of clouds?
Clouds reflect 23% of incoming solar radiation & absorb 26% of outgoing terrestrial radiation - therefore it has a radiative forcing of -20W/m(sq)
How do different types of clouds cause different levels of warming?
Cirrus = warming(greenhouse>albedo)
Deep cumulus clouds = neutral(greenhouse = albedo)
Stratus clouds = cool(albedo>greenhouse)
