GEOL 314 LECTURE 2 - The Greenhouse Gas Effect

Atmosphere

Free flowing mixed amalgamation of gases; includes Nitrogen, Oxygen, H2O vapor, Argon

Gases and EM wavelengths

Gases are not blackbodies, they absorb only infrared light and radiate it out into two directions (up and down); different gases absorb different parts of the infrared spectrum

Trace gases

Gases in the atmosphere in small concentrations that have a significant impact on the climate

Molecule geometry and radiation

Different molecules absorb different wavelengths of light, their geometry (and size) dictates what kind of radiation excites it by vibrational or rotational energy

Dipole

Segment of a molecule that is charged, usually due to molecular asymmetry

Gases and dipoles

Gases absorb IR radiation when molecule bonds move asymmetrically → asymmetry usually creates dipole moments

Molecule asymmetry

Gas molecules are excited by radiation causing stretching movements that result in kinetic energy that stretches bonds asymmetrically

Absorption spectra

The spectrum of electromagnetic wavelengths a molecule can absorb, out of the greenhouse gases H₂O has one of the widest

Greenhouse effect summary

1. Solar radiation is absorbed by Earth’s surface

2. Earth emits IR radiation

3. GGs in atmosphere absorb some IR radiation

4. IR radiation is re-emitted by the GGs both upwards to escape and back down to the Earth’s surface

5. Downwards IR radiation is absorbed causing a warming of the surface temperature

Band saturation

How much radiation has already been absorbed at a specific wavelength; if saturation is already close to 100% then the addition of CO2 won’t have a drastic effect

Layers of the atmosphere

Troposphere, stratosphere, mesosphere, thermosphere, exosphere; they all have the same proportion of gases but at different concentrations

Atmospheric window

A range of wavelength where there are no gases that absorb this light, meaning all of this light escapes into space

Climate forcing

Variables that change insolation absorbed by the Earth and/or the energy radiated back to space; examples are greenhouse gases and aerosols

Aerosols

Are solid or liquid particles in the atmosphere that cause climate forcing by changing planet albedo, stay in atmosphere for short period of time and mostly from fossil fuels

Sulfurous aerosols

Droplets of sulfuric acid and sulfate particles in air, raise atmospheric albedo as it is shiny and scatters sunlight to space so reduces sunlight absorbed by earth’s surface, also increases cloud development and precipitated out

Sulfurous aerosol sources

Natural source is volcanic eruptions but mostly from fossil fuels; impurities contain sulfur and nitrogen with the carbon and releases SO₂

Black carbon

Aerosols that decrease albedo as it enters atmosphere as soot so more light is absorbed, is a byproduct of incomplete combustion and stays in atm for a week

Effects of black carbon

When deposited on snow and ice, lowers albedo so more solar radiation is absorbed; also causes cryoconite holes which are dark-colored holes of aerosol deposition in ice/snow

Impactful climate forcers

Aerosols, methane and CO₂ have greatest impact on climate forcing