Greenhouse gases, climate change and air pollution
The greenhouse effect
- Short wavelength radiation from the Sun (mostly visible light) passes through the atmosphere and warms the surface.
- The warm surface gives off longer wavelength infrared radiation.
- Greenhouse gases (carbon dioxide, methane, water vapour) absorb infrared and re-emit it in all directions, some back towards the surface. Nitrogen, oxygen and argon do not.
The greenhouse effect itself keeps the Earth warm enough for life. The problem is adding more greenhouse gases, which warms it further.
Human activity, evidence and carbon footprint
- Carbon dioxide: burning fossil fuels, deforestation (burning, and fewer trees to absorb it).
- Methane: cattle, rice paddies, rotting waste in landfill.
- Most climate scientists agree, from peer-reviewed evidence, that human activity is warming the Earth. Models are simplified and the data is complex, so predictions carry uncertainty, and media reports can oversimplify.
- Possible effects: rising sea levels, more severe storms, changed rainfall and food production, species moving.
- A carbon footprint is the total greenhouse gas emitted over the life cycle of a product, service or event. Reduce it with renewable energy, efficiency, carbon capture and fewer journeys.
percentage change = (new value − original value) ÷ original value × 100
- Carbon dioxide rose from 318 ppm (1960) to 412 ppm (2020)
- increase = 412 − 318 = 94 ppm
- percentage increase = 94 ÷ 318 × 100 = 29.6% (3 s.f.)
Always divide by the starting value. Dividing by the final value gives a smaller, wrong answer.
Pollutants from burning fuels
| Pollutant | Where it comes from | Problem |
|---|---|---|
| carbon monoxide | incomplete combustion | toxic, colourless, odourless: the blood carries less oxygen |
| particulates (soot) | incomplete combustion | global dimming, lung damage |
| sulfur dioxide | sulfur impurities in fuels | acid rain, breathing problems |
| oxides of nitrogen | nitrogen and oxygen from the air react in hot engines | acid rain, breathing problems |
- S + O₂ → SO₂: 32 g of sulfur gives 32 + 2 × 16 = 64 g of sulfur dioxide
- 100 tonnes of coal with 2% sulfur contains 2 tonnes of sulfur
- so it makes 2 × 64 ÷ 32 = 4 tonnes of sulfur dioxide
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