BIOLOGY · Stage 7 · Chapter 4: The Physical Environment and Water Cycle
Biology 4.3 Global warming and the water cycle — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
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Lesson summary
4.3 Global warming and the water cycle — Alhussan International Academy — Biology (Stages 7–9) notes: Explain the greenhouse effect, how human activity enhances it and how global warming changes the water cycle and ecosystems.Fossil fuels — cars and electricity use them, and scie…
- Natural effect
- Importance
- Deforestation
- Measurements
- Thermometer records
- Physical changes
Section 1 of 8Fossil fuels and climate change
- Fossil fuels
- cars and electricity use them, and science has developed many ways of using them that bring great benefits to people everywhere.
- Crude oil from the ground is used to make fuels and many useful substances.
- Problem
- burning fossil fuels produces carbon dioxide, which is warming the Earth and causing climate change.
- Water cycle
- climate change is causing problems in the water cycle.
Section 2 of 8The greenhouse effect
- Natural effect
- the Earth is warmed by the Sun, and some heat is radiated back from the surface towards space.
- Greenhouse gases trap part of it and radiate it back to the surface.
- They include carbon dioxide, methane and water vapour.
- Importance
- it keeps the average temperature of the Earth at about 15 °C instead of about −18 °C, which makes life possible.
Section 3 of 8The enhanced greenhouse effect
- Global warming
- human activity has increased greenhouse gases, so more heat is trapped and the average temperature is rising.
- Fossil fuels
- burning them in power stations, vehicles and factories releases carbon dioxide.
- Deforestation
- fewer trees remove carbon dioxide by photosynthesis, and burning or rotting wood releases more.
- Farming
- cattle and rice paddies release methane.
- Measurements
- carbon dioxide in the air has risen by about 50% since the Industrial Revolution, and global average temperature has risen by roughly 1 °C.
Section 4 of 8Evidence for global warming
- Thermometer records
- they cover more than a century.
- Ice cores
- they show past carbon dioxide levels.
- Physical changes
- glaciers and Arctic sea ice are shrinking and sea level is rising.
- Living things
- plants flower earlier.
- Models
- scientists compare many data sets and use computer models to test predictions.
- Correlation
- carbon dioxide and temperature rising together does not prove a cause alone, but the known heat-trapping behaviour of the gases supports it.
Section 5 of 8Water on Earth and melting ice
- Salt water
- most of the water on Earth is salty.
- Fresh water
- about 2.5% of Earth's water is fresh.
- About 68.7% of fresh water is ice in glaciers and ice caps.
- About 30.1% is groundwater and 1.2% is surface water.
- Melting
- polar ice caps and glaciers are melting fast, so the store of fresh water gets smaller as it runs into the sea.
- Sea level rise
- it is caused by melting glaciers and by sea water expanding as it warms.
- Some island countries and low-lying land may disappear completely in the next 100 years.
Section 6 of 8Floods, droughts and the water cycle
- More evaporation
- a warmer surface means more water evaporates into the air, and warmer air holds more water vapour.
- Water vapour is itself a greenhouse gas, so more evaporation amplifies the warming in a feedback loop.
- Floods
- bigger clouds and bigger rainstorms often lead to flooding.
- Flooding destroys homes, washes away soil and causes loss of life.
- The most extreme rainfall happens over oceans and coastal areas, so coasts suffer most.
- Droughts
- in other places water evaporates from the soil but clouds are blown away so no rain falls.
- Droughts now last longer, and when it rains it is a violent downpour.
- Most of that water runs off and the rest evaporates quickly, so plants die and people and animals starve.
- Regions
- South Asia and northern Europe have more rainfall than normal, while the Mediterranean region and the Horn of Africa have less.
Section 7 of 8Effects on living things
- Habitats
- they change as temperature and rainfall change.
- Coral reefs
- they bleach when the ocean is too warm.
- Polar bears
- they lose the ice on which they hunt.
- Movement
- species may move towards the poles or to higher ground, and those that cannot adapt or move may become extinct.
- Crops
- yields may fall in places affected by drought.
Section 8 of 8Reducing global warming
| Action | How it helps |
|---|---|
| Use renewable energy | Less carbon dioxide from burning fuel |
| Plant trees | Absorb carbon dioxide |
| Save energy and recycle | Reduces fuel use |
| Protect forests | Keeps carbon stored |
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