1. Earth’s Climate System and Natural Change
Lesson 3: Earth’s Atmosphere
The atmosphere is the blanket of air and moisture that surrounds the earth, which is important for life and weather systems. It extends upward approximately 500 km, after which the vacuum of space begins.

2. Chemical Makeup
The air in our atmosphere is primarily composed of nitrogen (78%) and oxygen (21%). The numbers vary slightly depending on the source and how they round. Argon and CO2 are also relatively common, while the final portion (approximately 0.04%) is made up of several other gases such as neon, helium, methane, and ozone. Depending on where you are, you might find water vapour (close to Earth’s surface), and SO2 (in highly polluted areas). Note that this is an older graph, and that the concentration of CO2 has now reached 0.04%.

3. Carbon Dioxide
CO2 is present in trace amounts, but plays a crucial role as a greenhouse gas (GHG).
Current concentration is approximately % or 403 ppm (parts per million).
Prior to the industrial revolution, CO2 levels were around 275 ppm. The “safe” limit is considered to be around 350 ppm, and we have recently hit 400 ppm.
the-400-ppm-threshold-maybe-permanently/
GHG are gasses present in our atmosphere that are very effective at absorbing and emitting radiation as heat.
The global average is about 400 ppm.
We will talk more about greenhouse gasses and the greenhouse effect in our next lesson.

4. Importance of the Atmosphere
Natural Greenhouse Effect: helps control temperature extremes.
Ozone layer: protect us from UV radiation.
O2, CO2, H2O: all necessary for survival
Natural Greenhouse Effect, temperature extremes: warms Earth’s surface, reduces day/night extremes;
Ozone layer: protects against damaging ultraviolet (UV) radiation from the Sun;
Oxygen, Carbon Dioxide, Water Cycle: oxygen for humans and animals, carbon dioxide for plants, water for all (evaporation, transpiration from plants, precipitation);

5. Circulation in the Atmosphere
Convection cells force warm, moist air to raise at the equator and cold, dry air to sink at the poles.
Heat energy and moisture is transferred around the globe, to the poles.

6. Atmospheric Layers >690 km, satellites orbit here
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