What you’ll learn9 learning objectivesChoose one objective for a focused lesson, or study the complete topic.6.1.1Atmosphere boundary• Between Earth and space• Outer limit of biosphere• Composition and processes support lifeSyllabus objective6.1.2Atmospheric circulation• Differential heating creates tricellular model• Redistributes heat from equator to polesSyllabus objective6.1.3Greenhouse gases and aerosols• Absorb and re-emit infrared radiation• GHGs: water vapour, CO₂, methane, nitrous oxides• Aerosols: black carbonSyllabus objective6.1.4Greenhouse effect• Keeps Earth warmer than otherwise• Natural process enabling life• Enhanced greenhouse effect: human GHG accumulation → global warming• Climate change: broader range of resulting changesSyllabus objective6.1.5(HL)—Atmosphere as dynamic system• Physical processes: global warming, air movements• Chemical processes: ozone production from oxygenSyllabus objective6.1.6(HL)—Atmospheric pressure and altitude• Gravity pulls molecules to surface• Atmosphere thins with altitude• Standard lapse rate: ~1°C per 100mSyllabus objective6.1.7(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 warmingSyllabus objective6.1.8(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)Syllabus objective6.1.9(HL)—Life and atmosphere evolution• Life changed atmospheric composition• Photosynthesis: decreased CO₂, increased O₂• Allowed stratospheric ozone formation, metal oxidationSyllabus objective