Analyse the relationship between land cover change and climate change, including carbon, albedo and the enhanced greenhouse effect

What this dot point is asking

QCAA wants you to analyse a two-way relationship: land cover change drives climate change, and climate change drives further land cover change. "Analyse" means you break the relationship into its mechanisms (carbon, albedo, evapotranspiration) and show how they interact, including feedback loops. The enhanced greenhouse effect is the human-caused intensification of the natural greenhouse effect through added carbon dioxide, methane and other gases. Strong answers explain the mechanism, then apply it to named places, and identify at least one feedback loop.

The answer

The natural greenhouse effect and its enhancement

The natural greenhouse effect keeps Earth habitable: greenhouse gases (water vapour, carbon dioxide, methane) trap outgoing longwave radiation and warm the surface. The enhanced greenhouse effect is the human intensification of this process, mainly by burning fossil fuels and by changing land cover. Land cover change matters because vegetation and soil store enormous amounts of carbon, and changing the cover moves that carbon into or out of the atmosphere.

Mechanism 1: carbon

Forests, grasslands, soils, wetlands and peatlands are carbon stores. Living vegetation absorbs carbon dioxide through photosynthesis (a carbon sink). When forest is cleared and burned, the stored carbon is released as carbon dioxide (a carbon source), and the lost forest can no longer absorb future emissions. Tropical deforestation is therefore a double penalty: a pulse of emissions plus a permanent loss of uptake capacity. The Amazon, long a net carbon sink, has in parts shifted toward being a net carbon source where clearing and fire are heaviest.

Mechanism 2: albedo

Albedo is the proportion of incoming solar radiation a surface reflects. Bright surfaces (snow, ice, desert sand) have high albedo and reflect heat; dark surfaces (forest, ocean, dark soil) have low albedo and absorb heat. Land cover change alters albedo. Replacing dark boreal forest with bright snow-covered clearing can increase reflection, while melting bright Arctic sea ice exposes dark ocean that absorbs more heat. Albedo effects can either amplify or partly offset warming, which is why analysis matters more than a simple "clearing warms the planet" claim.

Mechanism 3: evapotranspiration and moisture

Vegetation moves water from soil to atmosphere through evapotranspiration, which cools the surface and recycles rainfall. Large forests like the Amazon generate much of their own rainfall through this recycling. Clearing reduces evapotranspiration, warms and dries the local climate, and can push a rainforest toward a drier savanna state. This is a land-cover driver of regional climate change distinct from the global carbon effect.

Feedback loops

The relationship is not one-directional. Feedback loops amplify change.

• Arctic permafrost. Warming thaws frozen ground, which releases methane and carbon dioxide, which causes more warming, which thaws more permafrost. This is a positive (amplifying) feedback.
• Amazon dieback. Clearing reduces rainfall recycling, drying the forest, increasing fire and tree death, which clears more forest, reducing rainfall further.
• Fire-climate feedback. Hotter, drier conditions increase fire, which removes vegetation and releases carbon, which adds to warming.

Australian savanna and managed burning

In northern Australia, savanna burning is both a source and a managed response. Late dry-season wildfires release large amounts of carbon and methane. Indigenous-led early dry-season patch burning reduces the intensity and area of fires, cutting net emissions. This shows land cover management used deliberately to influence the carbon balance.

Examples in context

Example 1. Amazon. Clearing releases stored carbon, reduces rainfall recycling and pushes the system toward dieback, where parts shift from sink to source.

Example 2. Arctic permafrost. Warming thaws frozen carbon stores, releasing methane and carbon dioxide in a powerful positive feedback.

Example 3. Northern Australian savanna. Indigenous early dry-season burning reduces the carbon and methane released by late-season wildfire, a managed land-cover response to climate change.