Topic 6: Atmosphere and climate change
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6.1 Introduction to the atmosphere
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
6.2 Climate change—causes and impacts
6.2.1Climate definition
• Typical atmospheric conditions • Seasonal temperature and precipitation variations
6.2.2Anthropogenic CO₂ emissions
• Atmospheric CO₂ concentration rising significantly • Accelerated since 1950 • Traced to Industrial Revolution (late 18th century)
6.2.3Ice core, tree ring, sediment data
• Positive correlation: atmospheric CO₂ and global temperatures • Data for past 800,000 years
6.2.4Enhanced greenhouse effect
• Anthropogenic GHG emissions • Led to global warming and climate change
6.2.5Climate change impacts on ecosystems
• Local to global scales • Affects resilience, leads to biome shifts • Examples: coral bleaching, desertification, ocean circulation changes
6.2.6Climate change impacts on societies
• Various scales and socio-economic conditions • Impacts resilience • Health, water supply, agriculture, infrastructure
6.2.7Climate change models
• Systems diagrams with feedback loops • Solar radiation variations, albedo changes, methane release
6.2.8Climate change planetary boundary
• Evidence suggests already passed
6.2.9Perspectives on climate change
• Influenced by many factors • Individual and societal levels
6.3 Climate change—mitigation and adaptation
6.3.1Global action required
• Avoid catastrophic climate change • International cooperation needed
6.3.2Decarbonization
• Reduce/end CO₂-emitting energy sources • Replace with renewable energy • Carbon neutrality goals
6.3.3Mitigation strategies
• Reduce global warming: household changes, geoengineering • Reduce GHG production: energy efficiency, renewables, food changes, carbon tax • Remove CO₂: carbon sinks, rewilding, afforestation, carbon capture
6.3.4Adaptation strategies
• Structural: flood defences, desalination, movable infrastructure • Non-structural: agricultural adaptation, vaccination, land zoning, building codes
6.3.5Adaptation plans
• National Adaptation Programmes of Action (NAPAs) • Individual to society scale
6.4 Stratospheric ozone
6.4.1Solar radiation spectrum
• Low frequency radio to high frequency gamma • Infrared, visible light, ultraviolet (UV)
6.4.2UV radiation danger
• Shorter wavelengths, higher frequencies, more energy • UVA, UVB, UVC damage organisms
6.4.3Stratospheric ozone protection
• Absorbs UV radiation from Sun • Protects living organisms from harmful effects
6.4.4UV radiation impacts
• Reduces photosynthesis in phytoplankton • DNA damage: mutations, cancer • Humans: sunburn, premature ageing, cataracts
6.4.5Ozone equilibrium
• Steady state between formation and destruction
6.4.6Ozone-depleting substances (ODSs)
• Destroy ozone molecules • Augment natural breakdown • Not a cause of global warming
6.4.7Ozone depletion effects
• More UVB reaches Earth's surface • Polar "ozone holes" in spring
6.4.8Montreal Protocol
• International treaty regulating CFCs and ODSs • Most successful international environmental cooperation
6.4.9Montreal Protocol success
• Prevented planetary boundary crossing