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.

Environment Change

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.

Recap

# 13.2 in one screen

## 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.

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