Global warming (AQA GCSE Biology): Revision Notes
Global warming
What are greenhouse gases?
Greenhouse gases are special gases in our atmosphere that trap heat from the sun. The main greenhouse gases are:
- Methane - comes from farming, especially rice fields and cattle
- Carbon dioxide - released when we burn fossil fuels like coal, oil, and natural gas
These gases work by absorbing heat radiation from the Earth's surface and then releasing it in all directions. This natural process helps keep our planet warm enough for life, but human activities are increasing the amount of these gases in the atmosphere.
This natural greenhouse effect is actually essential for life on Earth - without it, our planet would be too cold to support most forms of life. The problem is that human activities are making this effect much stronger than it should be naturally.
The greenhouse effect
The greenhouse effect is getting stronger because we're putting more greenhouse gases into the air. Scientists around the world agree that this is causing global warming and climate change.
This scientific agreement is based on:
- Thousands of research studies that other scientists have checked
- Detailed reviews of all this research
- Clear evidence from temperature and gas measurements over many years
The data shows that as carbon dioxide levels have risen since 1850, global temperatures have also increased. This isn't a coincidence - there's a clear connection between the two.
Human activities increasing greenhouse gases
We're adding more greenhouse gases to the atmosphere through these activities:
For methane:
- Farming rice in flooded fields
- Raising cattle for meat and dairy
- Other types of livestock farming
For carbon dioxide:
- Burning coal for electricity
- Using oil for transport and heating
- Burning natural gas for energy
- Using peat as fuel
Every time we use fossil fuels for energy, we release more carbon dioxide into the atmosphere.
Effects of global warming
Even a small rise in average temperature (just a few degrees) can cause major changes to our planet:
Climate changes
- More droughts in some areas
- Colder winters but hotter summers
- More flooding from extreme weather
- Changes in rainfall patterns
These climate changes don't affect all regions equally. Some areas might become much drier while others experience increased flooding, creating complex regional differences in climate impacts.
Rising sea levels
- Ice melting at the North and South Poles
- Seawater expanding as it gets warmer
- Coastal areas becoming flooded
- Some islands could disappear underwater
Effects on wildlife and plants
- Birds changing their migration routes and timing
- Animals and plants moving to different areas
- Some species struggling to survive in new conditions
- Changes in when plants flower and breed
Evidence from nature
Scientists have documented numerous examples of how climate change is already affecting natural systems around the world.
Worked Example: Bluebell Flower Timing Study
Scientists studied when bluebell flowers first appeared in a woodland between 1996 and 2012:
- 1996: First flowers on 23rd April
- 2000: First flowers on 13th April
- 2012: First flowers on 4th April
Analysis: The flowers are appearing earlier each year by approximately 10 days, suggesting that spring is starting sooner due to warmer temperatures. This shows how climate change is already affecting plant life cycles.
Future concerns
Warmer temperatures could allow tropical diseases to spread to new areas. Diseases that currently only exist in hot countries might move to places that were previously too cold for them. This could affect both human health and wildlife in these new areas.
Key Points to Remember:
- Greenhouse gases like methane and carbon dioxide trap heat in our atmosphere
- Human activities such as burning fossil fuels and farming are increasing these gas levels
- Global warming is supported by thousands of scientific studies showing clear evidence
- Small temperature rises can cause big changes to climate, sea levels, and wildlife
- Real examples like earlier bluebell flowering already show climate change is happening