Climate Change
⏱ 10 min✏️ Quiz at the end
The Natural Greenhouse Effect
The greenhouse effect is a natural process that makes Earth warm enough to support life. Without it, Earth's average temperature would be about -18°C instead of the current +15°C — roughly 33°C colder.
How it works:
- Solar radiation (visible light and UV) from the Sun passes through the atmosphere and reaches Earth's surface
- Earth's surface absorbs this energy and re-emits it as infrared radiation (heat)
- Greenhouse gases in the atmosphere absorb some of this infrared radiation and re-emit it in all directions, including back towards Earth
- This traps heat and warms the lower atmosphere
Key greenhouse gases:
- Carbon dioxide (CO2) — from respiration, decomposition, burning fuels
- Methane (CH4) — from livestock, rice paddies, landfills, wetlands
- Water vapour (H2O) — the most abundant greenhouse gas; naturally regulated
- Nitrous oxide (N2O) — from soils and fertilisers
- CFCs — man-made chemicals (now largely phased out)
The Enhanced Greenhouse Effect
Human activities have significantly increased concentrations of greenhouse gases, trapping more heat than the natural system — this is called the enhanced greenhouse effect, leading to global warming and climate change.
Since pre-industrial times (around 1750):
- CO2 levels have risen from ~280 ppm to over 420 ppm (as of 2024)
- Global average temperatures have risen by approximately 1.2°C
- Rate of temperature rise is accelerating
Causes of Climate Change
Burning Fossil Fuels
The single largest contributor. Burning coal, oil, and natural gas releases CO2 that was locked underground for millions of years.
- Electricity generation — coal and gas power stations
- Transport — cars, planes, ships burning petrol, diesel, and jet fuel
- Heating — gas boilers and furnaces
Deforestation
Trees absorb CO2 through photosynthesis. When forests are cut down:
- The stored carbon is released when trees decay or burn
- Fewer trees means less CO2 is removed from the atmosphere
Tropical deforestation accounts for roughly 10–15% of global CO2 emissions.
Agriculture
- Livestock (cattle, sheep) produce methane during digestion (enteric fermentation)
- Rice paddies release methane from waterlogged soils
- Nitrogen fertilisers release nitrous oxide (N2O), a potent greenhouse gas
Industry and Cement
- Cement production releases large amounts of CO2 (from heating limestone)
- Industrial processes such as steel, aluminium, and chemical manufacturing
Evidence for Climate Change
Scientists use multiple independent lines of evidence:
| Evidence | What it shows |
|---|---|
| Temperature records | Global average temperature has risen ~1.2°C since 1850 |
| Ice cores | Trapped air bubbles show CO2 levels and temperatures over 800,000 years |
| Sea level measurements | Global sea levels have risen 20–23 cm since 1900; rate is accelerating |
| Satellite data | Ice sheets in Greenland and Antarctica are losing mass |
| Glacier retreat | Most glaciers worldwide have retreated significantly |
| Ocean warming | Oceans absorb ~90% of excess heat; average temperature has risen |
| Biological indicators | Species shifting ranges poleward; earlier flowering/migration dates |
Consequences of Climate Change
Physical Effects
- Rising sea levels — from thermal expansion of water and melting ice; threatens low-lying coastal areas and islands
- Melting glaciers and ice caps — reduces freshwater supply for billions of people
- More extreme weather — stronger hurricanes, more intense rainfall, longer droughts, more wildfires
- Ocean acidification — oceans absorb CO2, forming carbonic acid; threatens coral reefs and shellfish
Ecological Effects
- Habitat loss — especially coral reefs, Arctic ecosystems, and mountain habitats
- Species extinction — organisms unable to adapt or migrate fast enough
- Ecosystem disruption — mismatches in timing (e.g., insect emergence before birds arrive)
Human Effects
- Food security — changing rainfall patterns and droughts affect crop yields
- Water scarcity — glacier melt reduces dry-season river flows
- Climate refugees — coastal flooding and desertification force people to move
- Health impacts — spread of tropical diseases to new areas; heat-related illness
Responses to Climate Change
Mitigation (Reducing Emissions)
| Strategy | How it helps |
|---|---|
| Renewable energy (solar, wind, hydro, tidal) | Replaces fossil fuels with zero-emission alternatives |
| Energy efficiency | Less energy needed = fewer emissions |
| Reforestation and afforestation | Trees absorb CO2 |
| Carbon capture and storage (CCS) | Removes CO2 from power station flue gases and stores underground |
| Reducing meat consumption | Cuts methane from livestock |
| Electric vehicles | Reduce transport emissions |
| International agreements | Paris Agreement (2015): limit warming to 1.5–2°C above pre-industrial levels |
Adaptation (Managing the Effects)
- Sea walls and flood defences
- Drought-resistant crop varieties
- Early warning systems for extreme weather
- Relocating vulnerable communities
Key Terms
| Term | Definition |
|---|---|
| Greenhouse gas | Gas that absorbs and re-emits infrared radiation, trapping heat |
| Enhanced greenhouse effect | Increased warming due to human-produced greenhouse gas emissions |
| Global warming | Long-term rise in Earth's average temperature |
| Climate change | Long-term shifts in global temperatures and weather patterns |
| Carbon footprint | Total greenhouse gas emissions caused by an individual or activity |
| Renewable energy | Energy from sources that are naturally replenished (sun, wind, water) |
| Mitigation | Actions that reduce greenhouse gas emissions |
| Adaptation | Adjustments made to cope with the effects of climate change |
Worked Example
Q: Explain how deforestation contributes to climate change.
Step 1: Trees absorb CO2 from the atmosphere during photosynthesis and store carbon in their wood and roots.
Step 2: When forests are cleared by burning or logging, the stored carbon is released as CO2 back into the atmosphere.
Step 3: With fewer trees, less CO2 is removed from the atmosphere by photosynthesis.
Step 4: The increased CO2 concentration enhances the greenhouse effect, trapping more heat and raising global temperatures.
Common Mistakes
- Confusing the greenhouse effect with ozone depletion — these are separate issues. Greenhouse gases trap heat; CFCs damage the ozone layer.
- Saying the greenhouse effect is bad — the natural greenhouse effect is essential for life; it is the enhanced greenhouse effect that is problematic.
- Confusing global warming and climate change — global warming refers specifically to rising temperatures; climate change includes all the effects (rainfall, extreme events, sea levels).
- Thinking climate change only means it gets hotter everywhere — some regions may experience colder winters, more rainfall, or other changes.
Tips and Tricks
- Exam questions often ask you to distinguish natural from human-caused (anthropogenic) climate change — focus on the word "enhanced."
- The key evidence students often forget: ice cores give a 800,000-year record of both temperature and CO2, showing they rise and fall together.
- Methane is a much more potent greenhouse gas than CO2 (about 25 times more warming per molecule) — useful for exam comparisons.
- Paris Agreement target: limit warming to 1.5°C above pre-industrial levels — this number appears frequently in exam questions.