6.1 Introduction to the atmosphere

Objective notes

9 learning objectives

6.1.1Atmosphere boundary

• Between Earth and space

• Outer limit of biosphere

• Composition and processes support life

6.1.2Atmospheric circulation

• Differential heating creates tricellular model

• Redistributes heat from equator to poles

6.1.3Greenhouse gases and aerosols

• Absorb and re-emit infrared radiation

• GHGs: water vapour, CO₂, methane, nitrous oxides

• Aerosols: black carbon

6.1.4Greenhouse effect

• Keeps Earth warmer than otherwise

• Natural process enabling life

• Enhanced greenhouse effect: human GHG accumulation → global warming

• Climate change: broader range of resulting changes

6.1.5(HL)—Atmosphere as dynamic system

• Physical processes: global warming, air movements

• Chemical processes: ozone production from oxygen

6.1.6(HL)—Atmospheric pressure and altitude

• Gravity pulls molecules to surface

• Atmosphere thins with altitude

• Standard lapse rate: ~1°C per 100m

6.1.7(HL)—Milankovitch cycles

• Affect solar radiation reaching Earth

• Climate cycles over tens to hundreds of thousands of years

• Three types: orbit shape, tilt angle, axis rotation

• Do not explain current warming

6.1.8(HL)—Global warming and geological cycles

• Moving away from glacial-interglacial cycle

• Quaternary period (2.5 million years)

• Current changes: rapid and anthropogenic (Anthropocene epoch)

6.1.9(HL)—Life and atmosphere evolution

• Life changed atmospheric composition

• Photosynthesis: decreased CO₂, increased O₂

• Allowed stratospheric ozone formation, metal oxidation