Greenhouse Gases: What They Are and Why They Matter
Greenhouse gases trap heat in Earth's atmosphere. Without them, the planet would be uninhabitable — but human emissions have tipped the balance into dangerous territory.
Greenhouse gases absorb and re-emit heat energy, trapping it in Earth's lower atmosphere. This process — the greenhouse effect — is what makes the planet habitable. Without it, average surface temperatures would be around -18°C. The problem is that human activity since industrialisation has increased greenhouse gas concentrations to levels that trap excess heat, driving dangerous global warming.
The Main Greenhouse Gases
| Gas | Global Warming Potential (100-yr) | Share of Australian emissions | Primary sources |
|---|---|---|---|
| Carbon dioxide (CO₂) | 1 | ~74% | Fossil fuel combustion, land clearing, cement production |
| Methane (CH₄) | 27–30× | ~17% | Livestock, coal mining, natural gas leaks, landfill |
| Nitrous oxide (N₂O) | 273× | ~5% | Agriculture, synthetic fertilisers, wastewater |
| Fluorinated gases (HFCs, SF₆) | 1,000–25,000× | ~3% | Refrigerants, industrial processes, electrical equipment |
Global Warming Potential (GWP) measures how much heat one tonne of a gas absorbs compared to one tonne of CO₂ over 100 years. Methane is 27–30 times more potent than CO₂ — which is why livestock agriculture (particularly beef and dairy cattle) is such a significant source of Australian emissions despite not burning fossil fuels directly.
What Is Happening to Concentrations
Atmospheric CO₂ has risen from about 280 parts per million (ppm) before industrialisation to over 420 ppm today — the highest level in at least 800,000 years based on ice core records. CSIRO monitors Australian atmospheric CO₂ at Cape Grim, Tasmania, which serves as a globally significant baseline measurement site. The rate of increase has accelerated in recent decades.
Why the Imbalance Matters
When greenhouse gas concentrations become imbalanced, excess heat is trapped. This raises surface temperatures, warms oceans, increases evaporation, energises storm systems and disrupts established weather patterns. For Australia, the consequences include longer and more intense fire seasons, more extreme rainfall events, prolonged droughts and rapid coral bleaching.
What Reduces Greenhouse Gas Emissions
- Replacing fossil fuel combustion with renewable electricity (solar, wind) — directly reduces CO₂
- Electrifying home heating, hot water and transport — captures the grid decarbonisation benefit automatically as the grid cleans up
- Reducing livestock consumption — targets the methane and N₂O pathway
- Improving land use and preventing deforestation — trees sequester CO₂; cleared land releases it
- Eliminating HFC refrigerants — the Kigali Amendment to the Montreal Protocol aims to phase down HFCs globally
Every tonne of CO₂ not emitted matters. The greenhouse effect operates on cumulative concentrations — emissions avoided today reduce the total long-term warming load, not just this year's temperature.