Global Warming & Climate Change
Understand the natural and enhanced greenhouse effect, the role of greenhouse gases, and the very real impacts of climate change on Australia and the world.
The Greenhouse Effect
The natural greenhouse effect is an essential process that keeps Earth warm enough to support life. Without it, Earth’s average temperature would be about −18°C instead of the current +15°C.
How the Greenhouse Effect Works
The Sun emits shortwave radiation (visible light) which passes through the atmosphere and warms Earth’s surface.
Earth’s surface absorbs this energy and re-emits it as longwave infrared radiation (heat).
Greenhouse gases in the atmosphere absorb and re-emit this infrared radiation, trapping heat and warming the lower atmosphere.
Greenhouse Gases & Human Activity
Human activities since the Industrial Revolution have increased the concentration of greenhouse gases, intensifying the natural greenhouse effect — this is the enhanced greenhouse effect, which is driving global warming.
| Gas | Symbol | Main human sources | Relative warming potential |
|---|---|---|---|
| Carbon dioxide | CO2 | Burning fossil fuels, deforestation | 1 (reference) |
| Methane | CH4 | Livestock, rice paddies, landfill | ~28× CO2 |
| Nitrous oxide | N2O | Fertilisers, agriculture | ~265× CO2 |
| Water vapour | H2O | Indirect (amplifies warming) | Natural amplifier |
The Key Evidence
- Atmospheric CO2 has risen from ~280 ppm (pre-industrial) to over 420 ppm (2024)
- Earth’s average temperature has increased by approximately 1.2°C since pre-industrial times
- Ice core data, satellite measurements and ocean heat content all confirm warming
Impacts on Australia
Australia is particularly vulnerable to climate change due to its already hot and dry climate, long coastlines, and unique biodiversity. Observed and projected impacts include:
Extreme Heat & Bushfires
More frequent and severe heatwaves and bushfire seasons. The 2019–20 “Black Summer” fires burned over 18 million hectares and were linked to climate change. Temperatures in some parts of Australia regularly exceed 45°C.
Rising Sea Levels
Melting polar ice and glaciers are causing sea level rise, threatening low-lying coastal communities and islands such as those in the Torres Strait. Australian sea levels have risen by ~20 cm since 1900.
Great Barrier Reef Bleaching
Warmer ocean temperatures cause coral bleaching, where corals expel their symbiotic algae and turn white. Mass bleaching events have occurred on the Great Barrier Reef (2016, 2017, 2020, 2022), threatening its long-term survival.
Changes to Agriculture
Changing rainfall patterns, longer droughts and more intense flooding are affecting agriculture in the Murray–Darling Basin and across rural Australia, impacting food production and water security.
Responding to Climate Change
Mitigation (reducing causes)
- Transitioning to renewable energy (solar, wind, hydro)
- Improving energy efficiency in buildings and transport
- Reducing deforestation and planting trees
- Reducing methane from agriculture
Adaptation (adjusting to changes)
- Building sea walls and flood defences for coastal towns
- Developing drought-resistant crop varieties
- Improving bushfire management and alert systems
- Upgrading infrastructure to cope with extreme heat
Key Vocabulary
| Term | Definition |
|---|---|
| Greenhouse effect | The process by which greenhouse gases trap heat in Earth's lower atmosphere, keeping the planet warm enough to support life. |
| Enhanced greenhouse effect | The intensification of the natural greenhouse effect due to increased greenhouse gas concentrations from human activities. |
| Global warming | The long-term rise in Earth's average surface temperature, primarily caused by the enhanced greenhouse effect. |
| Coral bleaching | The whitening of coral when rising sea temperatures cause corals to expel their symbiotic algae (zooxanthellae), threatening reef ecosystems. |
Worked Examples
Explaining why Venus is hotter than Mercury despite being further from the Sun.
Context: Mercury is closer to the Sun but has almost no atmosphere. Venus has a thick atmosphere of ~96% CO2.
Explanation: Venus experiences an extreme greenhouse effect. Its thick CO2 atmosphere traps almost all outgoing infrared radiation, raising the surface temperature to ~465°C.
Answer: Even though Mercury is closer to the Sun, Venus is hotter because its dense CO2 atmosphere creates an intense greenhouse effect that traps enormous amounts of heat. This illustrates the power of greenhouse gases.
Calculating a carbon footprint comparison.
Given: Driving a petrol car emits 0.21 kg CO2 per km. A 500 km road trip by car emits how much CO2? Compare to a train trip at 0.041 kg CO2/km.
Car: 0.21 × 500 = 105 kg CO2
Train: 0.041 × 500 = 20.5 kg CO2
Answer: The train produces approximately 5 times less CO2 than the car for the same trip (20.5 vs 105 kg). Switching to lower-emission transport is an effective way to reduce personal carbon footprints.
Distinguishing between weather and climate.
Weather refers to short-term atmospheric conditions at a specific place and time — e.g., “It is 38°C and sunny in Melbourne today.”
Climate refers to the long-term average pattern of weather in a region over many decades — e.g., “Melbourne has a temperate climate with hot, dry summers.”
Key point: A cold day in winter does not disprove global warming. Climate change refers to long-term shifts in average conditions, not individual weather events. Scientists use 30-year averages to define climate normals.
Knowledge Check
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Key Concepts Summary
- •The natural greenhouse effect traps heat in the atmosphere, keeping Earth habitable; greenhouse gases absorb and re-emit infrared radiation.
- •Human activities (burning fossil fuels, deforestation) increase greenhouse gas concentrations, intensifying the greenhouse effect — the enhanced greenhouse effect.
- •Key greenhouse gases include CO2, CH4, and N2O; Earth has already warmed by ~1.2°C above pre-industrial levels.
- •Australia faces impacts including more intense bushfires, coral bleaching on the Great Barrier Reef, sea level rise, and changing rainfall patterns.
- •Responses include mitigation (reducing emissions) and adaptation (adjusting to changes that are already occurring).