Causes: Melting Glaciers, Ice Sheets and Deforestation
This key knowledge asks you to distinguish natural from human causes of land cover change, understand how they interact (interconnection), and explain why certain causes are spatially associated with certain locations (spatial association).
Melting Glaciers and Ice Sheets
Natural Processes
- Solar variability: Milankovitch cycles (orbital eccentricity, axial tilt, precession) drive glacial-interglacial cycles over tens of thousands of years. We are currently in an interglacial period (the Holocene), so some natural warming would be expected
- Volcanic eruptions: Can cause short-term cooling by injecting aerosols into the stratosphere (e.g., Mt Pinatubo 1991 cooled global temperatures by ~0.5°C for 1–2 years), but this is temporary and does not explain sustained ice loss
- Ocean circulation: Warm Atlantic water intruding beneath ice shelves (e.g., Circumpolar Deep Water reaching Thwaites Glacier, Antarctica) accelerates basal melting — a natural mechanism amplified by ocean warming
Human Causes
- Greenhouse gas emissions: Burning of fossil fuels and deforestation have raised atmospheric CO₂ from ~280 ppm (pre-industrial) to over 420 ppm (2024). Enhanced greenhouse effect traps more longwave radiation, raising global mean temperatures by ~1.2°C above the pre-industrial baseline
- Black carbon (soot) deposition: Combustion particles settle on glacier surfaces, reducing albedo (from ~80% for clean ice to <50% for sooty ice), increasing heat absorption and melt rates
- Land use change: Deforestation reduces regional moisture recycling and can alter precipitation patterns affecting high-altitude snowpacks
Interconnection: The Ice-Albedo Feedback
Human emissions → atmospheric warming → glacier surface melt → darker ice/water exposed → reduced albedo → more solar radiation absorbed → accelerated melt. This positive feedback loop means human causes amplify natural processes.
Spatial Association
- Mountain glacier retreat is most pronounced where high-altitude temperatures are rising fastest — the Tibetan Plateau is warming at roughly double the global average rate (elevation-dependent warming)
- Arctic regions are warming 3–4 times faster than the global mean (Arctic amplification) due to sea ice loss reducing albedo
Deforestation
Natural Processes
- Wildfire: Natural ignition by lightning, especially in dry seasons, can remove forest cover (common in boreal Canada/Russia and tropical cerrado/savanna margins)
- Volcanic eruption and lava flow: Destroys forest in affected zones (e.g., eruptions in Indonesia, Hawaii)
- Insect outbreaks: Bark beetle epidemics, partly driven by warmer winters, have killed millions of hectares of boreal forest in Canada and the US
- Drought and wind: Prolonged drought weakens forest, increasing fire susceptibility
Important: Natural processes cause temporary disturbance; forests typically recover unless the disturbance is repeated or combined with human pressure.
Human Causes
- Commercial agriculture: Large-scale clearing for soy, palm oil, and cattle ranching (Brazil’s arc of deforestation; Indonesia’s palm oil expansion on Borneo and Sumatra)
- Subsistence farming: Smallholder slash-and-burn (shifting cultivation) in Congo Basin, Southeast Asia, and parts of South America
- Logging: Legal and illegal timber extraction opens the forest canopy and builds road networks enabling further clearing
- Infrastructure development: Roads, dams, and mining operations in the Amazon (e.g., BR-163 highway) create corridors of access that accelerate forest loss
- Urban expansion: Peri-urban growth encroaches on forest margins in rapidly urbanising tropical countries
- Fuelwood collection: Primary driver in sub-Saharan Africa (charcoal production for urban energy)
Interconnection: Forest-Climate Feedback
Deforestation releases stored carbon (tropical deforestation accounts for ~10% of global CO₂ emissions) → enhanced greenhouse effect → regional temperature rise → increased drought stress → forest dieback even in uncleared areas → further carbon release. This interconnection means deforestation is both a cause and a consequence of climate change.
Spatial Association
Deforestation is spatially associated with:
- Agricultural frontiers (areas where forest meets expanding farmland)
- Low-income tropical countries with high population growth and commodity export dependence
- Areas of poor governance and limited law enforcement
- Road networks and navigable rivers providing access
KEY TAKEAWAY: Both processes have natural and human causes, but human activity — primarily greenhouse gas emissions for glacier melt, and agricultural expansion for deforestation — is the dominant driver today. These causes are interconnected through climate feedbacks.
EXAM TIP: “Interconnection” is a core geographic concept in VCAA. Explain the feedback loop: how one cause connects to and amplifies another. For glacier melt: emissions → warming → melt → albedo reduction → more warming. For deforestation: clearing → carbon release → warming → drought → more tree death.
COMMON MISTAKE: Attributing glacier melt solely to natural warming cycles. The scientific consensus is that the current rate of ice loss cannot be explained without human-caused greenhouse warming. Distinguish between the background natural trend and the human amplification.
