Understanding how land cover has shifted over geological time provides the baseline against which human-driven change is measured. VCE Geography requires comparison across three time periods: the Last Glacial Maximum (LGM), the Holocene Climatic Optimum (HCO), and the present day.
During the LGM, global mean temperatures were approximately 4–7°C cooler than today. Ice sheets covered:
- North America as far south as the Ohio River (Laurentide Ice Sheet, ~13 million km²)
- Northern Europe including Britain and Scandinavia (Fennoscandian Ice Sheet)
- Southern South America and the Tibetan Plateau
Consequences for land cover:
- Sea level was ~120 m lower, exposing vast continental shelves (Sahul connected Australia and New Guinea; Beringia connected Asia and North America)
- Tropical forests contracted significantly; much of the Amazon was fragmented into isolated refugia surrounded by savanna and dry scrub
- Deserts expanded — the Sahara was larger and drier; Australian dunes were active as far south as the Murray-Darling Basin
- Grasslands and steppe expanded across Europe, northern Asia, and North America (the “mammoth steppe”)
- Tundra was pushed to much lower latitudes — southern France supported a periglacial landscape
As ice sheets retreated from ~18,000 years ago, global temperatures peaked during the HCO at 1–3°C above present in many mid-latitude regions. This period is also called the “Atlantic period” in European palaeoclimatology.
Key land cover changes:
- Tropical forests re-expanded rapidly — the Amazon and Congo basins were re-colonised by closed-canopy forest
- The Sahara experienced a “Green Sahara” phase: monsoon rains penetrated further north, supporting savanna, shallow lakes and human habitation (evidenced by rock art in the Fezzan, Libya)
- Boreal forests advanced northward into areas now occupied by tundra in Siberia and Canada
- Sea levels rose to roughly present levels by ~7,000 years ago, re-submerging coastal plains
- European forests reached their maximum post-glacial extent, blanketing most of the continent
| Feature | LGM (~20,000 BP) | HCO (~8,000 BP) | Present |
|---|---|---|---|
| Ice cover | Maximum extent (~30% of land) | Rapidly retreating | ~10% of land |
| Tropical forest | Fragmented / contracted | Expanded, continuous | Contracting (deforestation) |
| Deserts | Expanded | Contracted (Green Sahara) | Expanding in some regions |
| Tundra extent | Extended to mid-latitudes | Retreated north | Retreating further north |
| Sea level | ~120 m below present | Near present levels | Present levels (rising) |
These paleoclimatic shifts demonstrate that land cover is inherently dynamic — it responds to climate forcing on timescales of centuries to millennia. However, the current rate of change is unprecedented: deforestation, urbanisation and glacier retreat driven by anthropogenic warming are occurring over decades, not millennia.
KEY TAKEAWAY: Land cover has changed dramatically over time in response to natural climate cycles. The LGM saw ice expansion and forest contraction; the HCO saw warming, forest expansion, and a Green Sahara. The present period is distinctive because human activity — not just climate — is the primary driver of change.
EXAM TIP: You may be asked to compare land cover across time periods using maps or data. Always identify what changed, where the change occurred, and why it occurred (climate driver). Quantify change where possible (e.g., “ice sheets covered 30% of land during the LGM versus ~10% today”).
STUDY HINT: Think of the three time periods as a story: maximum ice (LGM) → warmth and expansion (HCO) → human-driven contraction (present). This narrative helps structure exam responses.
