HSC Geography · Human–Environment Interactions
13.2 Environmental & Human Causes of Climate Change
Chapter 13 · Climate Change · NESA Stage 6 (2022) · Revision deck
By the end you can…
Learning goals
- Separate natural from human causes.
- Rule out ice-age cycles & volcanoes for today's warming.
- Explain how humans disrupt the carbon cycle.
- Distinguish natural from enhanced greenhouse effect.
- Use the 800,000-year CO₂ record as proof.
Section 1
Two kinds of cause
Natural vs human
Natural
Orbital cycles, solar output, volcanoes, ocean circulation. Slow — millennia.
Human
Carbon-cycle disruption, fossil fuels, deforestation, enhanced greenhouse. Fast — ~250 yrs.
The recent change is far too rapid to be natural — and lines up with industrialisation.
Section 2 · Natural
Ice-age cycles
Milankovitch cycles
- Slow shifts in Earth's orbit & tilt change incoming solar radiation.
- They pace the ice ages over tens of thousands to 100,000+ years.
- Ruled out for today: wrong timing and far too fast.
To blame humans, you must first rule out the natural drivers.
Section 3 · Natural
Volcanic activity
Case study: Mount Pinatubo (1991)
~20 million tonnes of SO₂ → cooled Earth ~0.5°C for 1–2 years
Volcanoes cause short-term cooling, not warming — and all volcanoes' annual CO₂ is far less than human emissions.
EnvironmentChange
So volcanoes can't explain sustained warming either.
Section 4 · Human
Disrupting the carbon cycle
The carbon cycle, broken
Fossil fuels add carbon and deforestation removes sinks → a net rise in CO₂.
Section 5 · Human
The enhanced greenhouse effect
Natural vs enhanced
Natural
Keeps Earth ~33°C warmer — essential for life.
Enhanced (human)
Extra CO₂, methane, N₂O trap more heat → warming.
It's not the effect that's the problem — it's the human increase.
Section 6
The clincher: 800,000 years
CO₂ is off the chart
Today's CO₂ is outside the entire natural range — and spikes with industrialisation. Nature can't do this.
Pull it together
- Natural causes: orbital cycles, volcanoes — too slow / cooling / too little CO₂.
- Human cause #1: disrupting the carbon cycle (fossil fuels + deforestation).
- Human cause #2: the enhanced greenhouse effect.
- Clincher: 800,000-yr CO₂ record — today is off the chart.
Next: 13.3 — Impacts of climate change.