The Earth’s Atmosphere

Gas PercentNitrogen 78%

Oxygen 21%

Argon 0.93%

Carbon Dioxide (CO2)

0.037%

Neon, helium methane, ozone…

~0.04%

Also water vapor (most near the surface of the earth), dust and pollutants (e.g. sulfur dioxide)

0.039% means 390 ppm (“ppm” = parts per million)

Pre-industrial CO2 level: 275 ppmPresent CO2 level: 390 ppmSafe (?) CO2 level: 350 ppm

A Special Note on Carbon Dioxide• present in trace amounts, but important in its

effects:• a greenhouse gas (GHG) – a gas that is very

effective at absorbing (trapping) and emitting radiation as heat (infrared radiation)

Why is the atmosphere important?

1. Natural Greenhouse Effect, temperature extremes: warms Earth’s surface, reduces day/night extremes;

2. Ozone layer: protects against damaging ultraviolet (UV) radiation from the Sun;

3. Water Cycle: movement of water -evaporation, transpiration from plants, precipitation - provides for life;

Convection cells: Warm moist air rises at equator; Cold dry air sinks at the poles;Gives rise to winds;

Heat Energy and moisture: Transfers heat and moisture around the globe, to the poles;

Atmospheric Circulation

Atmospheric Layers