Land cover change · NSW Stage 6 Geography (2022) · Rose Bay Secondary College
Laptops down · copy the ✍️ notebook boxes as we go
What we're doing today ✍️ Copy into your notebook
Earth's systems have always changed — ice ages have come and gone for millions of years. What's new is that humans now set the pace, driving change in decades that nature took millennia to produce, and human change interacts with natural change to amplify it. This chapter is the foundation for the whole land-cover-change topic: get the natural-vs-human distinction right and every extended response gets easier.
By the end you can:
tell apart natural vs anthropogenic change;
explain the CO₂ warming mechanism;
read a temperature-anomaly graph;
account for why warming is spatially uneven;
quote verified Australian evidence.
Fossil-fuel energy — a human driver of change…and a human response: renewables
Two kinds of change ✍️ Copy into your notebook
Natural change — fires, floods, droughts, storms, volcanoes, earthquakes; long-term shifts in climate, water & nutrient cycles, succession.
Anthropogenic change — caused or accelerated by humans — population, pollution, fossil fuels, deforestation.
The two are not separate silos: they interact. In 1900 roughly 1.6 billion people made mostly local impacts; today over 8 billion people drive planetary ones — the shift that names the Anthropocene. And the interaction runs both ways: clearing vegetation doesn't just release carbon, it also strips the shade and moisture that keep a landscape cool, so land clearing warms the local climate on top of the global effect.
Land clearing — a human-induced change (NASA, Amazon)Drought — a natural hazard intensified by warming
📘 Syllabus: Human–Environment Interactions · land cover change🧭 Skill: Interpreting change over time
Tipping points ✍️ Copy into your notebook
A tipping point is a threshold beyond which change becomes self-sustaining and effectively irreversible on human timescales — the system flips to a new state and won't flip back just because you ease off. This is why systems don't always respond gradually or in proportion to the push they're given.
Greenland ice sheet — past a threshold, melt continues even if warming stops, because a lower, warmer surface keeps melting.
Amazon dieback — clearing enough forest can dry the region and flip it permanently to savanna, releasing its stored carbon.
🤔 Reflect & discuss
Why does a tipping point make “wait and see” a risky climate policy?
Ice-sheet & glacier melt is a candidate tipping elementArctic sea-ice loss feeds back on itself
📘 Syllabus: Human–Environment Interactions · land cover change🧭 Skill: Cause & consequence
Section 2
Natural change over time
Deep-time cycles ✍️ Copy into your notebook
“Climate change” just means a long-term shift in the planet's climate. Natural climate change is driven by Earth's axial tilt & orbit (Milankovitch cycles), solar output, ocean currents and volcanic activity — all altering the balance of incoming and outgoing energy.
At least 5 major ice ages; the last glacial period ended ~11,700 years ago.
A cooler Little Ice Age ran ~16th–19th century, before the current warming stage.
Thermometers only reach back to ~1850 — older climate comes from proxies.
Climate has always changed — what's unusual now is the rate and direction.
How do we know? Proxies
Ice cores — trapped air bubbles preserve ancient CO₂ and temperature, back 800,000+ years.
Tree rings — annual ring width records year-by-year growth and climate.
Sediment layers — ocean- and lake-bed chemistry archives past temperature.
Corals & pollen — growth bands and pollen counts extend the record.
Burn fossil fuels → release CO₂ → enhance the greenhouse effect → trap outgoing heat → warm the lower atmosphere.
Pre-industrial ~280 ppm → over 420 ppm now; the sharpest rise is since the 1950s — the “hockey stick.” The other half of the story is deforestation, whose spread is mapped from space by the Landsat programme.
The carbon numbers
Pre-industrial CO₂: ~280 ppm — stable for millennia.
Today: over 420 ppm — a rise of ~50% since 1850.
Steepest rise is since the 1950s (the “hockey stick”).
Land & ocean sinks absorb only about half of emissions.
Deforestation adds ~10% of emissions & strips the sink.
📘 Syllabus: Human–Environment Interactions · land cover change🧭 Skill: Interpreting a line graph · Skill 7
CO₂ through time ✍️ Copy into your notebook
Year / period
CO₂ (ppm)
Milestone
Pre-industrial
~280
stable baseline for millennia
1958
~315
Mauna Loa record begins (Keeling)
1990
~354
—
2013
~400
400 ppm passed
2023
~421
first year averaging above 420
Approximate; verify the current value at NOAA Mauna Loa (gml.noaa.gov/ccgg/trends).
A level not seen for millions of years — reached in ~250 years.
What the table shows
CO₂ was flat near 280 ppm for millennia.
It has risen ~50% since the Industrial Revolution.
The steepest rise is since 1958 (the Keeling curve).
400 ppm was passed in 2013 — then 420 a decade later.
📘 Syllabus: Human–Environment Interactions · land cover change🧭 Skill: Reading a data table
Deforestation: a double hit ✍️ Copy into your notebook
Clearing forest does two harmful things at once, which is why it is such a powerful driver of change.
Releases carbon — clearing or burning trees returns stored carbon to the atmosphere.
Removes the sink — fewer trees → less CO₂ absorbed → warming accelerates.
The scale is visible from orbit: NASA Earth Observatory publishes global maps that show the tropical clearing fronts advancing year on year. Because the two effects stack, deforestation contributes roughly 10% of human CO₂ emissions.
Emissions up AND absorption down — two effects from one action.
Cleared forest releases stored carbonDegraded land absorbs less — the sink shrinks
📘 Syllabus: Human–Environment Interactions · land cover change🧭 Skill: Cause & consequence
Section 4
Evidence of change today
The warming signal ✍️ Copy into your notebook
Global average surface temperature is now >1 °C above 1850. An anomaly is the difference from a long-term average, so “+1.1 °C” means 1.1 degrees above the baseline.
The signal isn't just air temperature: the same warming shows up in melting ice, rising and acidifying seas, and fiercer extremes.
The warming numbers
Warming so far: >1.1°C above the 1850 baseline.
The 10 warmest years on record are all since 2014.
2023 was the warmest year in the instrumental record.
Each recent decade is warmer than the one before it.
The ocean holds ~90% of the extra heat in the system.
📘 Syllabus: Human–Environment Interactions · land cover change🧭 Skill: Reading an anomaly graph
Four physical signals ✍️ Copy into your notebook
Melting iceRising seasWorse extremesMore CO₂
Ice
Glaciers & ice sheets in retreat.
Seas
Sea level rising.
Oceans
Acidifying — the “other CO₂ problem.”
Extremes
Heatwaves, droughts, fire, heavy rain.
🤔 Reflect & discuss
Why is ocean acidification a problem even if the planet did not warm at all?
Why the ocean matters
The ocean has absorbed ~25% of human CO₂ emissions.
Dissolved CO₂ lowers seawater pH — acidification.
This dissolves the shells of corals, molluscs & plankton.
It also stores ~90% of the extra heat in the system.
That stored heat drives longer, fiercer marine heatwaves.
Watch: mapping change from space ✍️ Copy into your notebook
We've said satellites track land cover change — here is how. This short film from NASA Goddard shows how the Landsat satellites detect exactly where and when trees fall, turning decades of imagery into maps of forest loss. It's a working example of the global maps that make human-induced change measurable rather than merely asserted.
As you watch, note: (1) how Landsat detects a tree has fallen; (2) why a 50-year image archive matters for spotting change; (3) one way these maps could inform a decision (policy, conservation or farming).
BoM/CSIRO State of the Climate 2022 ✍️ Copy into your notebook
The climate numbers below come from BoM/CSIRO; for land cover specifically, Australia's change is mapped by DEA Land Cover (Geoscience Australia) and assessed in State of the Environment 2021.
Fire
Longer seasons & more extreme fire weather.
Cyclones
Fewer, but more intense.
Alpine snow
Depth & snow days falling since the 1950s.
Oceans
Acidifying, warming — more marine heatwaves.
Verifiable Australian evidence — always cite the report & year, and check for a newer edition.
📘 Syllabus: Human–Environment Interactions · land cover change🧭 Skill: Sourcing verified data
Build an answer
“Account for the spatial variation in the rate of global warming.”
✍️ How to build your answer
State your view in one sentence.
Give a reason (a “… because …”).
Support it with an example.
Note the other side, then conclude.
Name a fast region and a slow region, give the mechanism for each (ice–albedo feedback; aerosol masking), then say why the global average alone is misleading.
Sources & explore further ✍️ Copy into your notebook
Every claim in this lesson traces back to a primary source — a satellite dataset, a monitoring record or an official assessment. Use these to check the data yourself and to build a research task. Being able to name and cite a source is exactly what lifts a Band 5–6 response above a Band 3–4 one.
Primary source — original data or an official assessment, not someone's summary of it. Cite these, not a random blog.