Climate change refers to long-term shifts in global or regional temperatures, precipitation, wind patterns and other climate parameters. The IPCC defines it as “a change in the state of the climate that can be identified (e.g. using statistical tests) by changes in the mean and/or variability of its properties and that persists for an extended period, typically decades or longer.”
| Weather | Climate |
|---|---|
| Atmospheric conditions at a specific time and place | Long-term average of atmospheric conditions (30+ years) |
| Varies day to day | Changes over decades to centuries |
| Example: “It rained today in Melbourne” | Example: “Melbourne’s average annual rainfall is ~600 mm” |
Common misconception: A cold winter does not refute climate change — climate refers to long-term averages and trends, not individual weather events.
The natural greenhouse effect is essential for life. The enhanced greenhouse effect occurs when human activities increase concentrations of greenhouse gases beyond natural levels, trapping additional heat in the atmosphere.
| Feature | Natural GHE | Enhanced GHE |
|---|---|---|
| Cause | Natural atmospheric composition | Human GHG emissions |
| Effect | Maintains habitable temperatures (~+33°C) | Additional warming beyond natural baseline |
| CO$_2$ level | ~280 ppm (pre-industrial) | >420 ppm (2024) |
| Temperature trend | Relatively stable (Holocene) | Rapid upward trend since ~1850 |
| Reversibility | Stable natural process | Requires active emissions reduction |
The IPCC (2021) states that human influence has warmed the climate at an unprecedented rate in recorded history. Observable evidence includes:
| Concept | Definition |
|---|---|
| Radiative forcing | Change in energy flux in the atmosphere caused by a driver (e.g. doubling CO$_2$); measured in W m$^{-2}$ |
| Climate sensitivity | How much global average temperature rises for a doubling of CO$_2$ (estimated 2.5–4°C) |
| Tipping points | Thresholds beyond which climate systems shift abruptly to a new state |
| Feedback loops | Processes that amplify (positive) or dampen (negative) initial warming |
REMEMBER: ‘Enhanced greenhouse effect’ is the VCAA-preferred term for human-caused climate change via GHG emissions. Always distinguish it from the natural greenhouse effect, which is beneficial. Note the distinction: the natural GHE is the mechanism; the enhanced GHE is what happens when that mechanism is amplified by human emissions.
