Global environmental problems — A/L Biology

What must I remember about Global environmental problems?

• Enhanced Greenhouse Effect and Anthropogenic Global Warming: Greenhouse gases (CO2 from fossil fuel combustion/deforestation, CH4 from ruminants/paddy cultivation, N2O from fertilizers, CFCs) absorb outgoing longwave infrared radiation, trapping heat and raising global mean surface temperatures.
• Consequences of Climate Change: Thermal expansion of oceans and polar ice sheet melting causing Sea Level Rise, ocean acidification (dissolved CO2 forms carbonic acid, reducing carbonate ion availability for calcifying corals and mollusks), extreme weather events (prolonged droughts, erratic monsoons, intense cyclones).
• Stratospheric Ozone Layer Depletion: Chlorofluorocarbons (CFCs) and halons release free chlorine and bromine radicals under UV radiation; a single chlorine radical catalyzes the breakdown of over 100,000 ozone molecules (O3 -> O2), thinning the protective ozone shield and permitting harmful UV-B radiation to cause skin melanomas, cataracts, and phytoplankton mortality.
• Acid Rain (Acid Deposition): Atmospheric emissions of sulfur dioxide (SO2 from coal power plants) and nitrogen oxides (NOx from vehicle exhaust) react with water vapor to form sulfuric (H2SO4) and nitric (HNO3) acids, lowering precipitation pH below 5.6; causes soil aluminum toxicity, forest dieback, and freshwater aquatic mortality.
• Deforestation and Desertification: Unsustainable clearance of tropical forests for agriculture drives topsoil erosion, hydrological disruption, loss of carbon sinks, and desertification in semi-arid zones.

Test yourself (1 minute)

1. Montreal Protocol vs Kyoto/Paris Agreements

   The Montreal Protocol (1987) successfully phased out ozone-depleting substances (CFCs), hailed as the most effective global treaty; Paris Agreement (2015) commits nations to limit global warming well below 2.0°C (ideally 1.5°C) above pre-industrial baselines.

2. Ocean Acidification chemistry

   Atmospheric CO2 dissolves in ocean water to produce carbonic acid: CO2 + H2O <-> H2CO3 <-> H+ + HCO3-; excess H+ ions react with carbonate (CO3²-), depleting carbonate needed by calcifying corals to build CaCO3 skeletons.

3. Eutrophication sequence

   Excessive agricultural runoff of nitrates and phosphates -> algal bloom -> algae die and sink -> aerobic saprotrophic bacteria multiply -> biological oxygen demand (BOD) skyrockets -> dissolved O2 crashes (hypoxia) -> mass fish kills.

Practise Global environmental problems questions today

Source: NIE G.C.E. (A/L) Biology Syllabus & Resource Book, Unit 6

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Next in the syllabus

Where does Global environmental problems fit in the syllabus?

Year 2 · Term 2