Download 05_The Atmosphere

The Earth’s Atmosphere
Gas
Nitrogen
Percent
78%
Oxygen
21%
Argon
0.93%
Carbon Dioxide
(CO2)
0.039%
Neon, helium
methane, ozone…
~0.04%
Also water vapor (most near the surface of the
earth), dust and pollutants (e.g. sulfur dioxide)
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)
0.039% means 390 ppm (“ppm” = parts per million)
Pre-industrial CO2 level: 275 ppm
Present CO2 level: 390 ppm
Safe (?) CO2 level: 350 ppm
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. Oxygen, Carbon Dioxide, Water Cycle: oxygen
for humans and animals, carbon dioxide for
plants, water for all (evaporation, transpiration
from plants, precipitation);
Atmospheric Circulation
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 Layers
>690 km, satellites orbit here
85-690 km, ions (aurora, northern
lights) here, space shuttle orbits
here
50-85 km, “meso” = “middle”,
meteors burn up here
20-50 km, highest concentration
of ozone (“ozone layer”), planes
0-20 km (8 km at poles), most
of the atmosphere’s moisture,
weather takes place here