GCSE Biology revision

Global warming

Biodiversity and the effect of human interaction on ecosystems

AQA 4.1.1.1

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AQA student objectives

Learning pathway

All · Most · Some

ALL 🎯

Identify and describe What is Global Warming?, The Greenhouse Effect: Step by Step and Human Activities That Increase CO₂ Levels in the context of global warming.

MOST 🎯🎯

Explain the relationships between What is Global Warming?, The Greenhouse Effect: Step by Step and Human Activities That Increase CO₂ Levels and how they contribute to global warming.

SOME 🎯🎯🎯

Apply and analyse knowledge of What is Global Warming?, The Greenhouse Effect: Step by Step and Human Activities That Increase CO₂ Levels to interpret unfamiliar information about global warming.

Revision summary

Key knowledge

Read on screen, then print for Cornell-style active revision.

What is Global Warming?

Global warming is the gradual increase in the Earth's average temperature caused by a build-up of greenhouse gases in the atmosphere.
The two main greenhouse gases responsible are carbon dioxide (CO₂) and methane (CH₄).
A small amount of greenhouse gases is natural and keeps the Earth warm enough to support life, but excess amounts cause dangerous overheating.

1. What is Global Warming?AQA

Notes

Global warming is the gradual increase in the Earth's average temperature caused by a build-up of greenhouse gases in the atmosphere.
The two main greenhouse gases responsible are carbon dioxide (CO₂) and methane (CH₄).
A small amount of greenhouse gases is natural and keeps the Earth warm enough to support life, but excess amounts cause dangerous overheating.

The Greenhouse Effect: Step by Step

Infrared radiation from the Sun travels through space and enters the Earth's atmosphere, warming the Earth's surface.
Some of the heat radiated back from the Earth's surface escapes into space, helping to regulate temperature.
Greenhouse gases such as CO₂ and CH₄ trap and re-radiate heat back towards Earth, preventing it from escaping into space.
As concentrations of greenhouse gases increase, more heat is trapped, causing the Earth's average temperature to rise.

2. The Greenhouse Effect: Step by StepAQA

Notes

Infrared radiation from the Sun travels through space and enters the Earth's atmosphere, warming the Earth's surface.
Some of the heat radiated back from the Earth's surface escapes into space, helping to regulate temperature.
Greenhouse gases such as CO₂ and CH₄ trap and re-radiate heat back towards Earth, preventing it from escaping into space.
As concentrations of greenhouse gases increase, more heat is trapped, causing the Earth's average temperature to rise.

Human Activities That Increase CO₂ Levels

Burning fossil fuels such as coal, oil, and gas releases large amounts of CO₂ into the atmosphere.
Burning wood and peat also releases stored carbon dioxide directly into the atmosphere.
Deforestation means fewer trees are available to absorb CO₂ through photosynthesis, so atmospheric levels rise.
The thermal decomposition of calcium carbonate (limestone) in the building industry releases CO₂ as a by-product.

3. Human Activities That Increase CO₂ LevelsAQA

Notes

Burning fossil fuels such as coal, oil, and gas releases large amounts of CO₂ into the atmosphere.
Burning wood and peat also releases stored carbon dioxide directly into the atmosphere.
Deforestation means fewer trees are available to absorb CO₂ through photosynthesis, so atmospheric levels rise.
The thermal decomposition of calcium carbonate (limestone) in the building industry releases CO₂ as a by-product.

Slash-and-Burn Deforestation

Slash-and-burn deforestation involves cutting down and burning areas of forest so the land can be used for agriculture.
Burning the trees releases stored CO₂ directly into the atmosphere, and the destroyed trees can no longer absorb CO₂.
Rice paddy fields created on cleared land release large quantities of methane (CH₄) as vegetation decomposes in waterlogged conditions.
Cattle farmed on cleared land produce significant amounts of methane through burping and flatulence, further increasing greenhouse gas levels.

4. Slash-and-Burn DeforestationAQA

Notes

Slash-and-burn deforestation involves cutting down and burning areas of forest so the land can be used for agriculture.
Burning the trees releases stored CO₂ directly into the atmosphere, and the destroyed trees can no longer absorb CO₂.
Rice paddy fields created on cleared land release large quantities of methane (CH₄) as vegetation decomposes in waterlogged conditions.
Cattle farmed on cleared land produce significant amounts of methane through burping and flatulence, further increasing greenhouse gas levels.

Evidence: CO₂ Emissions and Temperature Change

Data from 1960 to 2010 shows that both global average temperatures and CO₂ emissions per capita have increased over time.
Although there are year-to-year fluctuations in temperature and emissions, the overall trend for both is clearly upward.
The correlation between rising CO₂ levels and rising temperatures supports the link between greenhouse gas emissions and global warming.

5. Evidence: CO₂ Emissions and Temperature ChangeAQA

Notes

Data from 1960 to 2010 shows that both global average temperatures and CO₂ emissions per capita have increased over time.
Although there are year-to-year fluctuations in temperature and emissions, the overall trend for both is clearly upward.
The correlation between rising CO₂ levels and rising temperatures supports the link between greenhouse gas emissions and global warming.

Melting Ice Caps and Rising Sea Levels

Global warming causes polar ice caps and glaciers to melt, which leads to a rise in global sea levels.
Low-lying areas such as Bangladesh, Pacific islands, and coastal cities like London are at risk of flooding as sea levels rise.
A significant rise in sea level would submerge vast areas of land, destroying habitats and displacing millions of people.

6. Melting Ice Caps and Rising Sea LevelsAQA

Notes

Global warming causes polar ice caps and glaciers to melt, which leads to a rise in global sea levels.
Low-lying areas such as Bangladesh, Pacific islands, and coastal cities like London are at risk of flooding as sea levels rise.
A significant rise in sea level would submerge vast areas of land, destroying habitats and displacing millions of people.

Impact on Arctic Food Chains

Algae trapped in Arctic sea ice form the base of the Arctic food chain, supporting zooplankton, shrimp, seals, and polar bears.
As sea ice melts, algae populations decline, reducing food availability for zooplankton and causing a knock-on effect throughout the food chain.
Polar bears also rely on sea ice as a platform for hunting seals, so the loss of ice directly reduces their ability to find food.
These combined effects mean polar bear populations are threatened by starvation due to the loss of Arctic sea ice.

7. Impact on Arctic Food ChainsAQA

Notes

Algae trapped in Arctic sea ice form the base of the Arctic food chain, supporting zooplankton, shrimp, seals, and polar bears.
As sea ice melts, algae populations decline, reducing food availability for zooplankton and causing a knock-on effect throughout the food chain.
Polar bears also rely on sea ice as a platform for hunting seals, so the loss of ice directly reduces their ability to find food.
These combined effects mean polar bear populations are threatened by starvation due to the loss of Arctic sea ice.

Expansion of Deserts and Habitat Loss

Rising temperatures cause desert regions to expand as surrounding land becomes hotter and drier, a process known as desertification.
The expansion of deserts reduces the area of habitable land available to plants and animals, leading to habitat loss.
As habitats are lost or altered, many species face extinction, resulting in a significant reduction in biodiversity.

8. Expansion of Deserts and Habitat LossAQA

Notes

Rising temperatures cause desert regions to expand as surrounding land becomes hotter and drier, a process known as desertification.
The expansion of deserts reduces the area of habitable land available to plants and animals, leading to habitat loss.
As habitats are lost or altered, many species face extinction, resulting in a significant reduction in biodiversity.

Changes in Migration Patterns and Species Distribution

Many animals rely on environmental cues such as day length and temperature to trigger migration to new areas each year.
Global warming disrupts these biological cues, causing changes in migration patterns for birds, locusts, and other migratory species.
The distribution of species — where they live and in what numbers — changes as temperatures and weather patterns shift across the globe.
These disruptions to ecosystems contribute further to the overall loss of biodiversity caused by climate change.

9. Changes in Migration Patterns and Species DistributionAQA

Notes

Many animals rely on environmental cues such as day length and temperature to trigger migration to new areas each year.
Global warming disrupts these biological cues, causing changes in migration patterns for birds, locusts, and other migratory species.
The distribution of species — where they live and in what numbers — changes as temperatures and weather patterns shift across the globe.
These disruptions to ecosystems contribute further to the overall loss of biodiversity caused by climate change.

Key Exam Points on Global Warming

The two main greenhouse gases to name in an exam are carbon dioxide (CO₂) and methane (CH₄).
In the greenhouse effect, reduced energy loss into space means heat is re-radiated back to Earth, raising global temperatures.
Biological consequences of global warming include melting ice caps, rising sea levels, habitat loss, changes in species distribution, altered migration patterns, and reduced biodiversity.

10. Key Exam Points on Global WarmingAQA

Notes

The two main greenhouse gases to name in an exam are carbon dioxide (CO₂) and methane (CH₄).
In the greenhouse effect, reduced energy loss into space means heat is re-radiated back to Earth, raising global temperatures.
Biological consequences of global warming include melting ice caps, rising sea levels, habitat loss, changes in species distribution, altered migration patterns, and reduced biodiversity.