The Atmosphere, Climate Change, Biodiversity, and Sustainable Use

Atmospheric Composition & Key Concepts

• Atmospheric Composition:

  • Nitrogen ($N_2$): $78\%$

  • Oxygen ($O_2$): $21\%$

  • Trace gases (mainly carbon dioxide, $CO_2$): $1\%$

• Greenhouse Effect: Natural balancing of greenhouse gases (GHGs) regulates Earth's temperature to sustain life, whereas the enhanced greenhouse effect results from excessive emissions trapping too much heat.

• Global Warming: Rise in Earth's average surface temperature caused by the enhanced greenhouse effect.

• Carbon Sink: Natural system (soil, water, plant) absorbing and storing $CO_2$.

• Carbon Footprint: Amount of $CO_2$ released due to individual or group energy needs.

• Ozone Depletion: Reduction in ozone concentration in the stratospheric ozone layer.

Major Greenhouse Gases

• Carbon Dioxide ($CO_2$):

  • Released via cellular respiration and organic decomposition.

  • Generated by burning fossil fuels for electricity and transport.

  • Produced through chemical reactions in cement and fertilizer manufacturing, as well as veld fires and domestic wood burning.

• Methane ($CH_4$):

  • Second largest contributor to the enhanced greenhouse effect; human activities account for over $60\%$ of total atmospheric $CH_4$

  • Produced naturally via anaerobic decomposition in wetlands, melting permafrost and polar ice, and marine organism decomposition in seawater.

  • Generated by intensive agriculture (ruminant digestion, decomposing dung/compost) and industrial processes (fossil fuel refining, drilling/fracking).

Enhanced Greenhouse Effect & Impacts

• Climate & Weather: Sharply rising temperatures, increased heatwaves, extreme storms, altered rainfall patterns, and prolonged drought periods.

• Ocean Systems: Coastal flooding from rising sea levels; warmer seawater destroys coral reefs (which act as carbon and methane sinks); ocean acidification ($CO_2$ forming carbonic acid) degrades marine exoskeletons and corals.

• Food Security & Land: Reduced crop yields due to changing seasons; desertification affects $33\%$ of global land, placing $1\text{ billion}$ people at risk of famine ($90\%$ of South Africa is classified as desert or semi-desert).

Deforestation & Ecosystem Destruction

• Global Impact: Felling and burning indigenous forests accounts for an estimated $20\%$ of global greenhouse gas emissions.

• Primary Causes: Land clearance for farming/urbanization, commercial logging, removal of non-indigenous plantations, mining, fuelwood harvesting, bark/root stripping for traditional medicines, forest fires, and acid rain.

• Ecological Effects:

  • Destroys natural carbon sinks (e.g., rainforests of the Congo Basin), keeping $CO_2$ trapped in the atmosphere.

  • Increases atmospheric $CH_4$ via termite activity on dead timber and livestock grazing on cleared land.

  • Causes soil degradation, nitrogen loss, severe erosion, frequent flooding/mudslides, and rapid species extinction (estimated $50{,}000$ species annually).

Alien Plant Invasions & Biodiversity Loss

• Exotic Plant Impacts:

  • Imported species (e.g., Jacaranda, Water hyacinth, pine tree, wattle tree, eucalyptus tree) outcompete indigenous flora due to a lack of natural enemies.

  • Deep root systems deplete groundwater tables.

  • Incomplete litter decomposition causes nutrient leaching and increases soil acidity.

  • Reduces livestock pasture quality and narrows the genetic pool, threatening native species with extinction.

• Threats to Biodiversity: Habitat destruction is the primary cause of biodiversity loss, aggravated by developments like golf estates that cause water depletion, eutrophication, pollution, and habitat fragmentation.

Sustainable Resource Use & Indigenous Knowledge

• Sustainable Use: Fulfilling present human needs while preserving adequate supply for future generations.

• Devil's Claw (Harpagophytum procumbens):

  • Medicinal Use: Relieves pain, inflammation, arthritis, lower back pain, and digestive disorders.

  • Sustainable Measures: Harvest secondary tubers only (leaving main roots intact), establish commercial cultivation, regulate wild harvesting, and protect natural habitats.

• Rooibos (Aspalathus linearis):

  • Medicinal Use: Antioxidant-rich, caffeine-free herbal tea used for allergies, digestive problems, and mild skin irritations.

  • Sustainable Measures: Cut stems instead of uprooting plants, replant after harvest, conserve fynbos habitat, and promote sustainable farming.