Section 1 of 6The greenhouse effect
1Sunlight arrives
- Sunlight arrives Radiation from the Sun passes through the atmosphere and warms the Earth's surface.
2Infrared emitted
- Infrared emitted The warm surface gives out infrared radiation.
3Gases absorb
- Gases absorb Greenhouse gases such as carbon dioxide and methane absorb some of it and re-emit it in all directions.
4Surface warms
- Surface warms Part of this energy returns to the surface, so more greenhouse gas means a warmer planet.
Section 2 of 6The balance of fossil fuels
Coal
- Coal Produces the most carbon dioxide per unit of energy of the three fossil fuels.
Natural gas
- Natural gas Produces the least carbon dioxide, so replacing coal with gas is a step in the right direction, though it is not a complete solution.
UK trend
- UK trend Over about thirty years fossil fuel use has fallen sharply while renewables have grown, from a very small share to roughly a third of supply.
Section 3 of 6Reducing carbon emissions
Cutting carbon emissions
Renewables
- Renewables Government grants have encouraged wind and solar farms.
- They give out no carbon dioxide when generating, but may be unreliable.
Nuclear power
- Nuclear power Low carbon and reliable, but old stations are closing and new ones are expensive and controversial.
Energy storage
- Energy storage Better ways to store energy would let us rely more on solar and wind, which only produce power when the weather allows.
Decision making
- Decision making Science identifies the issues, but political, social, ethical and economic factors decide what is done.
Section 4 of 6Comparing energy options
| Option | Carbon dioxide emitted | Drawback |
|---|---|---|
| Coal | High | Most polluting fossil fuel |
| Natural gas | Lower than coal | Still a fossil fuel and finite |
| Wind and solar | None when generating | Intermittent supply; need storage; some public opposition |
| Nuclear | Very low | Radioactive waste; high cost and slow to build |
Section 5 of 6Key terms
| Term | Meaning |
|---|---|
| Greenhouse effect | The warming of the Earth because gases in the atmosphere absorb and re-emit infrared radiation. |
| Global warming | A rise in the Earth's average surface temperature. |
| Carbon-neutral | Not adding extra carbon dioxide to the atmosphere overall. |
| Intermittent | Not available all the time, e.g. solar power at night. |
| Fossil fuel | A fuel such as coal, oil or gas formed from ancient living organisms. |
Section 6 of 6Exam technique
1
Saying greenhouse gases reflect the Sun's light. They absorb and re-emit infrared radiation from the ground.
2
Claiming natural gas is carbon-free. It produces less carbon dioxide than coal but not zero.
3
Ignoring the practical problems of wind and solar, such as unreliable supply.
4
Mixing up the ozone layer problem with global warming.