HSC Geography · Human–Environment Interactions
12.1 Natural & Human-Induced Change
Land cover change · NESA Stage 6 Geography (2022) · Revision deck
By the end you can…
Learning goals
- Tell apart natural and anthropogenic change.
- Explain how fossil fuels and deforestation drive warming.
- List the physical evidence of climate change and read an anomaly graph.
- Explain why warming is spatially uneven.
- Quote Australian evidence (BoM/CSIRO).
Section 1
Change in Earth's natural systems
Two kinds of change
Natural change
Fires, floods, droughts, storms, volcanoes, earthquakes; long-term shifts in climate, water & nutrient cycles, succession.
Human-induced (anthropogenic)
Population growth, pollution, fossil-fuel burning, deforestation → climate change, erosion, poor air, water scarcity.
1900: ~1.6 billion people, local impacts. Today: 8 billion+, planetary impacts — the idea behind the Anthropocene.
Tipping points
A tipping point is a threshold beyond which change becomes self-sustaining and effectively irreversible on human timescales.
- Greenland ice-sheet melt
- Amazon rainforest dieback
Use the term precisely — not just “a bad point,” but a threshold triggering cascading feedbacks.
Section 2
Natural change over time
Deep-time cycles
- Drivers: axial tilt/orbit, solar output, ocean currents, volcanoes.
- ≥ 5 major ice ages; last glacial ended ~11,700 years ago.
- Little Ice Age: ~16th–19th century, before current warming.
Climate has always changed — the question is the rate and direction of today's change.
How do we know? Proxies
Ice cores
Trapped air = past CO₂ & temperature, 800,000+ years.
Tree rings
Ring width = yearly growth conditions.
Sediment & coral
Layer chemistry = past ocean & temperature.
Section 3
Anthropogenic climate change
The fossil-fuel driver
Burn fossil fuels → release CO₂ → enhance greenhouse effect → trap heat → warm the lower atmosphere.
Pre-industrial ~280 ppm → over 420 ppm now; sharpest rise since the 1950s (the “hockey stick”).
Deforestation: a double hit
Releases carbon
Clearing/burning trees puts stored carbon back into the air.
Removes the sink
Fewer trees → less CO₂ absorbed → warming accelerates.
Section 4
Evidence of change today
The warming signal
>1 °C since 1850; each recent decade warmer than the last; 10 warmest years all since 2014; 2023 the warmest on record.
Four physical signals
Ice
Glaciers & ice sheets melting.
Ocean chemistry
Acidifying (the “other CO₂ problem”).
Weather
Extremes more frequent & severe.
Section 5
Spatial variation in warming
Warming is uneven
Case study: Arctic amplification
~4× global rate. Ice–albedo feedback: melting bright ice exposes dark ocean that absorbs more heat → more melting.
InterconnectionChangeScale
Section 6
An Australian perspective
BoM/CSIRO State of the Climate 2022
+1.47 °C
Air temperature since 1910.
+1.05 °C
Sea-surface temp since 1900.
−15%
SW WA cool-season rainfall since 1970.
Longer fire seasons, more intense cyclones, less alpine snow, acidifying seas. Cite the report & year.
Pull it together
- Natural vs anthropogenic change — humans now set the pace.
- CO₂: 280 → 420+ ppm; deforestation is a double hit.
- Evidence: warming >1 °C, melting ice, rising & acidifying seas, worse extremes.
- Warming is uneven — Arctic ~4× (ice–albedo feedback).
- Australia: +1.47 °C, drying south-west (BoM/CSIRO 2022).
Next: 12.2 Land cover change at a global scale.