Global warming (AQA GCSE Biology Combined Science): Revision Notes
Global warming
What are greenhouse gases?
Greenhouse gases are special gases in our atmosphere that trap heat. The main ones you need to know are:
- Methane - comes from farming (rice fields and cattle)
- Carbon dioxide - comes from burning fossil fuels like coal, oil, natural gas and peat
These gases work by absorbing heat radiation from Earth's surface. They then release this heat in all directions. This process helps keep Earth warm enough for life.
The greenhouse effect is actually essential for life on Earth. Without greenhouse gases, our planet would be about 33°C colder than it is today, making it too cold to support most life forms.
The greenhouse effect
The greenhouse effect is getting stronger because humans are putting more greenhouse gases into the atmosphere. This is causing global warming and climate change.
Scientists agree this is happening based on:
- Thousands of research papers that have been checked by other scientists
- Systematic reviews of all this research
The scientific consensus on human-caused climate change is overwhelming, with over 97% of actively publishing climate scientists agreeing on this conclusion.
Evidence for global warming
Temperature records show that Earth has been getting warmer since around 1900. At the same time, the amount of carbon dioxide in the atmosphere has been rising. This isn't a coincidence - the two are linked.
The data shows that temperatures have risen by about 0.8°C since 1850, with the steepest rise happening after 1980. Carbon dioxide levels have increased from about 290 parts per million to over 380 parts per million.
Effects of global warming
Even a small temperature rise of just a few degrees can cause big problems:
Climate changes
- More droughts in some places
- Colder winters in some areas
- Hotter summers
- More flooding from extreme weather
Rising sea levels
This happens because:
- Ice sheets and glaciers melt, adding water to oceans
- Warmer water expands and takes up more space
Sea level rise is one of the most concerning long-term effects of global warming, potentially affecting millions of people living in coastal areas worldwide.
Effects on species
- Birds change when they migrate
- Animals move to different areas to find suitable climates
- Some species might not be able to adapt fast enough
Real example - Bluebell flowers
Worked Example: Seasonal Changes in Bluebell Flowering
Scientists studied when bluebell flowers first appeared each spring from 1996 to 2012. They found that:
Data collected:
- In 1996, first flowers appeared on 23 April
- By 2012, first flowers appeared on 4 April
- This shows flowers are blooming about 19 days earlier
Analysis: This suggests spring is arriving earlier due to warmer temperatures. However, we can't be completely sure because the data only covers one location and one species.
Scientific significance: This type of phenological data (timing of biological events) provides important evidence for climate change impacts on ecosystems.
Other impacts of climate change
Warmer temperatures could help tropical diseases spread to new areas. This is because:
- Disease-carrying insects like mosquitoes might survive in places that were previously too cold
- Warmer weather could help diseases spread faster
This expansion of disease vectors is a significant public health concern as climate change progresses.
Key Points to Remember:
- Greenhouse gases (methane and carbon dioxide) trap heat in our atmosphere
- Human activities like farming and burning fossil fuels are increasing these gases
- Global warming is supported by thousands of scientific studies
- Effects include climate changes, rising sea levels, and impacts on wildlife
- Even small temperature rises can cause big environmental changes