Climate Change
Section: Biology | Syllabus: Cambridge Lower Secondary Checkpoint Science (0893)
What is Climate Change?
- Climate change refers to long-term changes in global or regional temperature and weather patterns
- primarily caused by increased greenhouse gas emissions from human activities
| Aspect | Weather | Climate |
|---|---|---|
| Timeframe | Short-term (day-to-day) | Long-term (30+ years) |
| Definition | Atmospheric conditions at a specific time | Average weather patterns over time |
The Greenhouse Effect
- The greenhouse effect is a natural process where certain gases in the atmosphere trap heat from the Sun
- this keeps Earth warm enough for life to exist
Natural Greenhouse Effect
- Keeps Earth at an average temperature of 15°C, instead of −18°C
- Essential for life to exist on Earth
- without it, Earth would be too cold for most organisms
Enhanced Greenhouse Effect
- Enhanced greenhouse effect: the increased warming of Earth due to higher concentrations of greenhouse gases from human activities trapping more heat in the atmosphere
- Human activities have increased greenhouse gas concentrations
- more heat is trapped in the atmosphere
- global temperatures are rising — this is global warming
Natural greenhouse effect compared with the enhanced greenhouse effect caused by human activity
Greenhouse Gases
- Several gases in the atmosphere contribute to the greenhouse effect
- each has different sources and warming potentials
| Greenhouse Gas | Chemical Formula | Main Sources | Impact |
|---|---|---|---|
| Carbon Dioxide | CO₂ | Burning fossil fuels, deforestation | Main contributor to climate change |
| Methane | CH₄ | Cattle farming, rice fields, landfills | 25× more potent than CO₂ |
| Water Vapour | H₂O | Evaporation, increases with temperature | Most abundant greenhouse gas |
| Nitrous Oxide | N₂O | Fertilisers, industrial processes | 300× more potent than CO₂ |
- Although methane and nitrous oxide are more potent greenhouse gases, carbon dioxide is released in much larger quantities
- this is why CO₂ is the main contributor to climate change overall
Causes of Climate Change
- Human activities are the primary drivers of current climate change
- these activities release large amounts of greenhouse gases into the atmosphere
Burning Fossil Fuels
- Coal, oil, and natural gas burned for electricity, heating, and transport
- releases massive amounts of CO₂
- accounts for approximately 75% of greenhouse gas emissions
Deforestation
- Cutting down forests for agriculture, timber, and development
- reduces CO₂ absorption, since there are fewer trees for photosynthesis
- burning forests releases stored carbon as CO₂
Agriculture
- Cattle produce methane during digestion
- Rice paddies release methane
- Fertilisers release nitrous oxide
Industrial Processes
- Cement production releases CO₂
- Chemical manufacturing releases various greenhouse gases
Waste and Landfills
- Decomposing organic waste produces methane
Global greenhouse gas emissions by source
Effects of Climate Change
- Climate change has wide-ranging effects on the environment, ecosystems, and human society
- these effects are becoming more severe as temperatures continue to rise
| Effect | What's Happening | Impact |
|---|---|---|
| Rising Temperatures | Global average temperature increased by ~1.1°C since 1880 | Heatwaves, droughts, wildfires |
| Melting Ice | Polar ice caps and glaciers melting | Loss of habitat for polar animals |
| Rising Sea Levels | Sea levels risen ~20cm since 1900 | Coastal flooding, island nations threatened |
| Extreme Weather | More frequent and intense storms, floods, droughts | Crop damage, property destruction, loss of life |
| Ocean Acidification | Oceans absorb CO₂, becoming more acidic | Coral bleaching, shellfish threatened |
| Species Extinction | Habitats changing faster than species can adapt | Loss of biodiversity |
| Food and Water Shortage | Droughts affect crop yields; water scarcity | Hunger, migration, conflict |
Impact on Species and Ecosystems
- When the environment changes due to climate change, species populations respond in different ways
- some can adapt, while others face extinction
| Response | Explanation | Example |
|---|---|---|
| Adapt | Species change behaviour or physiology to survive | Birds migrating at different times |
| Migrate | Move to more suitable habitats | Fish moving to cooler waters |
| Decrease | Population numbers decline due to stress | Coral reefs dying from heat stress |
| Go Extinct | Unable to adapt or move; species dies out | Polar bears losing sea ice habitat |
- Climate change is happening faster than most species can adapt naturally
- this leads to increased extinction risk for many organisms
Other, Non-Warming Threats to Populations
- Not every population decline is caused directly by rising temperatures — poaching/hunting and habitat loss are separate human-caused threats that can drive a species toward extinction alongside, or even without, climate warming
- Worked Example: The Black Rhino
- The world population of black rhinos fell sharply from around 1960 to 1995, then slowly recovered from 1995 to 2020
- Reasons for the decline: poaching for their horns, and habitat loss (e.g. from deforestation)
- Reason for the recovery: conservation efforts, such as anti-poaching protection and habitat/species protection programmes, allowed the population to slowly grow back
- This shows that conservation action — not just reducing emissions — can directly reverse a population decline caused by hunting and habitat loss
Solutions to Climate Change
Interactive revision notes, videos and practice questions load below.