Pollution

The natural greenhouse effect.

• Sun's rays warm Earth's surface.
• Earth radiates HEAT back as INFRARED radiation.
• Greenhouse gases (CO₂, methane, water vapour) ABSORB this infrared.
• Re-emit some back toward Earth → keeps Earth warmer.
• Without it: Earth would be ~-18°C (frozen). Greenhouse effect makes Earth ~+15°C — habitable.

Human enhancement.

• Burning FOSSIL FUELS releases CO₂.
• Cattle (livestock) and rice paddies release METHANE.
• Deforestation REDUCES CO₂ absorption.
• Industrial processes release other greenhouse gases.

Net effect: more greenhouse gas in atmosphere → more heat trapped → temperatures rising.

Evidence of warming:

• Average global temperature up ~1.1°C since 1880.
• Ice caps and glaciers melting.
• Sea levels rising (~20 cm).
• Hotter heatwaves more frequent.
• Acidifying oceans (CO₂ + water → carbonic acid).

Consequences (in detail):

1. Sea level rise.

• Melting glaciers + thermal expansion of warmer water.
• Coastal flooding; threatens low-lying nations (Bangladesh, Pacific islands).

2. Extreme weather.

• More frequent + severe hurricanes, droughts, floods, heatwaves.

3. Habitat changes.

• Species migrating poleward.
• Polar species (polar bears) running out of habitat.
• Coral bleaching from warmer + more acidic oceans.

4. Agriculture.

• Heat stress, droughts → crop failures.
• Some areas may benefit (longer growing seasons); many worse off.

5. Biodiversity loss.

• Many species can't adapt fast enough.
• Combined with habitat destruction → extinction crisis.

Worked qualitative. Why does CUTTING TREES make global warming WORSE in TWO ways?

• (1) Trees absorb CO₂ via photosynthesis. Cutting REMOVES this CO₂ sink.
• (2) Burning the wood RELEASES the carbon stored in it.
• Double impact: less absorption + more release.

Cambridge tip. Memorise the chain: SUN → EARTH → INFRARED → GAS TRAPS → WARMING. Specifically state INFRARED.

Formation:

1. Burning FOSSIL FUELS (especially coal) releases SULFUR DIOXIDE (SO₂) and NITROGEN OXIDES (NOₓ).
2. In atmosphere, these react with water vapour and oxygen.
3. Form SULFURIC ACID (H₂SO₄) and NITRIC ACID (HNO₃).
4. Carried in clouds → fall as rain → ACID RAIN.

Effects:

1. Forests damaged.

• Acid leaches nutrients (Ca²⁺, Mg²⁺) from soil.
• Damages waxy cuticle on leaves → makes trees vulnerable.
• Leaves drop early; trees weaken; sometimes die.

2. Lakes acidified.

• Acid rain runs into lakes.
• Lake pH drops below tolerable for most fish.
• Eggs especially sensitive → no reproduction.
• Lake becomes 'crystal clear' but lifeless.

3. Buildings + statues eroded.

• Limestone + marble (calcium carbonate) react with acid.
• Cathedrals, monuments slowly dissolved.
• Famous examples: Parthenon (Athens), Taj Mahal (India).

4. Soil acidification.

• Reduces crop yields.
• Releases TOXIC aluminium ions normally bound to soil.

Reducing acid rain:

• Filter SO₂ from power station emissions (scrubbers).
• Catalytic converters in cars (reduce NOₓ).
• Reduce fossil fuel use overall.
• Add LIME (calcium hydroxide) to acidified lakes — short-term fix.

Reduced significantly in Europe + N America since 1980s due to clean air laws. Still major problem in some developing countries.

Worked qualitative. Why does acid rain kill fish even when the lake's chemistry seems otherwise fine?

• Low pH affects fish gills directly.
• Low pH also releases toxic aluminium from sediments.
• Many fish species can't reproduce below certain pH.
• Especially salmon, trout — they're sensitive.

Cambridge tip. Always state SO₂ + NOₓ → acidic rain → effects. Cambridge marks each link.

Plastic pollution.

• Plastic doesn't biodegrade → accumulates in oceans, soil.
• Microplastics in food chain → in human bodies.
• Animals (turtles, seabirds) eat plastic → die.
• ~10 million tonnes enter oceans annually.

Oil spills.

• Tanker accidents, drilling leaks.
• Oil coats animals (birds can't fly, mammals lose insulation).
• Toxic to fish + sea life.
• Decades to recover.

Sewage pollution.

• Untreated sewage → eutrophication + spread of disease.
• Treatment plants remove most pollutants but sometimes overflow in storms.

Heavy metals.

• Lead, mercury, cadmium from industry, batteries, mining.
• Persistent — don't break down.
• BIOACCUMULATE in food chains: small amounts in plankton → concentrated in big fish (tuna, sharks).
• Cause neurological damage, developmental problems.

Pesticides.

• Persistent ones (DDT) accumulate in food chains.
• Killed many birds (eggshells thinned) → DDT banned in many countries.
• Caused decline of bald eagle, peregrine falcon — recovered after ban.

Noise pollution.

• Stresses wildlife.
• Disrupts whale + dolphin communication (sonar in oceans).
• Affects bird breeding.

Worked qualitative. Why is MERCURY in TUNA an example of BIOACCUMULATION?

• Mercury enters water from industrial sources.
• Plankton absorb tiny amounts.
• Small fish eat plankton → more mercury.
• Bigger fish eat smaller → more mercury.
• Apex predators (tuna, shark) accumulate the most.
• Pregnant women warned to limit tuna intake.

Cambridge tip. Memorise BIOACCUMULATION as the technical term. Cambridge marks it.