Lesson 1 of 9 / Climate change, food and disease vectors
Connect human activities to warming
How do energy use, forest clearance and food choices add greenhouse gases?
In this lesson: Explain the contribution of fossil fuels, deforestation and meat production to CO2 and methane accumulation over recent centuries.
About 5 min
The key ideaFossil-fuel use, forest clearance and food production can add CO2 or methane and reduce carbon uptake. Their accumulation changes the balance between energy entering and leaving Earth.
Explore the idea
Follow a gas from its source
Burning fossil fuel transfers carbon from underground stores into atmospheric CO2. Methane leakage can add another emission route.
Explanation
Over the last few centuries, industrial activity, transport and increasing energy demand have expanded the burning of coal, oil and natural gas. Burning fossil carbon transfers carbon from long-term underground stores into atmospheric carbon dioxide. Methane can also escape during fossil-fuel extraction and handling.
Forests store carbon in vegetation and soil. Clearing and burning vegetation releases carbon dioxide; decomposition of cleared material can release more. Removing growing trees also reduces an existing route for carbon uptake by photosynthesis. The timing depends on what happens to the wood and soil, so not all stored carbon is necessarily emitted immediately.
Food choices influence production demands. Ruminants such as cattle release methane from microbial digestion. Feed production, manure handling, energy use and clearance for pasture or feed can add further emissions. Increasing demand for meat can therefore increase greenhouse-gas emissions, especially where it drives more ruminant production or forest conversion.
Earth absorbs incoming solar energy and emits longer-wavelength infrared radiation. Carbon dioxide and methane absorb and re-emit some outgoing infrared radiation. Increasing their concentrations alters the energy balance and warms the surface and lower atmosphere until energy loss adjusts. This enhanced greenhouse effect is distinct from depletion of the ozone layer.
Step by step
- 1
Name the activity
Fossil-fuel combustion, forest clearance or a specific production process.
- 2
Name the gas and carbon route
Explain where CO2 or methane is released, or where uptake is reduced.
- 3
Link to warming
Accumulating greenhouse gases affect outgoing infrared energy.
Worked example
One cleared forest, two effects
A forest is cleared and its vegetation burned to create cattle pasture. Explain two separate reasons this can increase warming pressure.
One way to explain it
Burning transfers stored vegetation carbon into atmospheric CO2, while removing growing trees reduces future carbon uptake. Cattle can add methane from microbial digestion, providing a further emission route.
Why this answer works
- Distinguish release of a carbon store from loss of an uptake process.
- Connect livestock to methane rather than treating every emission as CO2.
Is this true? "Global warming is mainly caused by a hole that lets extra sunlight through the ozone layer."
The greenhouse mechanism concerns absorption and re-emission of outgoing infrared radiation. Ozone depletion is a different atmospheric process.