Climate Change

Natural greenhouse effect. Without atmosphere, Earth's average surface temperature would be ~−18 °C — too cold for life as we know it. Atmospheric greenhouse gases trap heat, raising the average to ~15 °C.

Mechanism:

1. Short-wavelength visible/UV radiation from the Sun passes through the atmosphere and warms the Earth's surface.
2. The Earth re-emits this energy as longer-wavelength infrared radiation.
3. Greenhouse gases (CO₂, CH₄, H₂O vapour, N₂O) absorb the infrared and re-emit some downward.
4. This traps heat near the surface.

Major greenhouse gases.

Gas	Main human sources	Relative potency (per molecule, 100-yr)
Carbon dioxide (CO₂)	Burning fossil fuels, deforestation, cement	1× (reference)
Methane (CH₄)	Cattle, rice paddies, landfill, fossil fuel leaks	~28×
Nitrous oxide (N₂O)	Fertilisers, industry	~265×
Water vapour (H₂O)	Natural; amplifies warming as air warms	—

Enhanced greenhouse effect. Human emissions raise concentrations of greenhouse gases, particularly CO₂ (from ~280 ppm pre-industrial to >420 ppm today). The result is global warming and broader climate change.

Biological impacts.

• Range shifts. Species move poleward and to higher altitudes as their preferred temperatures shift. Some can't move fast enough or have nowhere to go (e.g. mountaintop species).
• Phenology mismatches. Spring activities (flowering, migration, breeding) occur earlier with warming. If species don't shift in sync (e.g. caterpillars emerge before birds arrive to feed chicks), populations decline.
• Coral bleaching. Warm water expels symbiotic algae (zooxanthellae) from coral; corals lose colour and starve. The 2016 and 2024 global mass bleaching events damaged much of the Great Barrier Reef.
• Ocean acidification. $\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \rightarrow \text{H}^+ + \text{HCO}_3^-$. Higher [H⁺] (lower pH) reduces availability of carbonate (CO₃²⁻), making it harder for corals, molluscs and plankton to form CaCO₃ shells.
• Sea-level rise from melting glaciers/ice caps and thermal expansion of seawater inundates coastal habitats.
• Extreme weather (heatwaves, droughts, floods) stresses ecosystems and crops.

Positive feedbacks (amplify warming):

• Ice-albedo feedback — melting ice exposes darker ocean/land that absorbs more heat.
• Permafrost methane release — thawing permafrost releases CH₄ stored in soil, accelerating warming.
• Loss of vegetation carbon sinks — droughts and fires release stored carbon.

Mitigation strategies.

Strategy	Mechanism
Renewable energy (solar, wind, hydro, nuclear)	Avoid emitting CO₂
Energy efficiency	Less fuel burned per unit of work
Reforestation / afforestation	Photosynthetic carbon sink
Reduce methane (manure capture, drained rice paddies, leak reduction)	Cuts potent GHG
Dietary change (less beef)	Lower farm methane + land use
Carbon capture and storage	Sequester CO₂ underground
Behavioural change	Reduced flying, public transport, recycling

International agreements (e.g. Paris Agreement, 2015) target keeping warming below 1.5 °C. Tutopiya schools can use Internal Assessments to investigate local impacts (water quality, biodiversity).