Climate Change and Human Activity

While the previous lesson showed that climate has always changed naturally, the scientific consensus is overwhelming: the rapid warming observed since the mid-20th century is primarily caused by human activities. This lesson examines the enhanced greenhouse effect, the evidence for human-caused climate change, its impacts on people and environments, and the strategies being used to address it. This is one of the most important topics in GCSE Geography because it connects physical processes with human decision-making and global consequences.

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The Greenhouse Effect: Natural vs Enhanced

The Natural Greenhouse Effect

The natural greenhouse effect is essential for life on Earth. Without it, the average surface temperature would be approximately -18°C instead of the current +15°C.

1. Short-wave solar radiation from the Sun passes through the atmosphere and heats the Earth's surface.
2. The warm Earth's surface emits long-wave (infrared) radiation back towards space.
3. Greenhouse gases in the atmosphere absorb some of this outgoing long-wave radiation and re-radiate it in all directions, including back towards the surface.
4. This trapping of energy warms the lower atmosphere and the surface — the greenhouse effect.

The Enhanced Greenhouse Effect

The enhanced greenhouse effect occurs when human activities increase the concentration of greenhouse gases in the atmosphere beyond their natural levels. More greenhouse gases trap more heat, causing the planet to warm beyond its natural temperature.

graph TD
    A["Sun emits short-wave radiation"] --> B["Passes through atmosphere<br/>Heats Earth's surface"]
    B --> C["Earth emits long-wave<br/>(infrared) radiation"]
    C --> D["Greenhouse gases absorb<br/>and re-radiate heat"]
    D --> E["Some heat escapes to space"]
    D --> F["More heat trapped by<br/>INCREASED greenhouse gases<br/>→ Enhanced warming"]
    F --> G["Global temperatures rise"]

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Key Greenhouse Gases

Gas	Chemical Formula	Main Human Sources	Contribution to Enhanced Greenhouse Effect	Atmospheric Lifetime
Carbon dioxide	CO₂	Burning fossil fuels (coal, oil, gas), deforestation, cement production	~65% of total warming	300–1,000 years
Methane	CH₄	Agriculture (rice paddies, livestock — especially cattle), landfill sites, fossil fuel extraction	~16% of total warming	~12 years
Nitrous oxide	N₂O	Agricultural fertilisers, burning fossil fuels, industrial processes	~6% of total warming	~114 years
Fluorinated gases	HFCs, PFCs, SF₆	Industrial processes, refrigeration, air conditioning	~2% of total warming	Up to 23,000 years
Water vapour	H₂O	Not directly produced by humans, but warming increases evaporation, amplifying the greenhouse effect	Acts as a feedback mechanism	Days to weeks

Exam Tip: CO₂ gets the most attention because it is the most abundant human-produced greenhouse gas and persists in the atmosphere for centuries. But methane is approximately 80 times more potent as a greenhouse gas than CO₂ over a 20-year period, even though it has a much shorter atmospheric lifetime.

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Evidence for Human-Caused Climate Change

The evidence that current warming is primarily human-caused is extensive and comes from multiple independent sources:

Temperature Records

• Global average surface temperature has risen by approximately 1.1°C since the pre-industrial period (1850–1900).
• The 20 warmest years on record have all occurred since 1998. The years 2015–2023 were the nine warmest ever recorded.
• The rate of warming has accelerated: the planet warmed by 0.08°C per decade between 1880 and 1980, but by 0.18°C per decade since 1981 — more than twice as fast.

Ice Loss

• The Arctic sea ice extent has declined by approximately 13% per decade since satellite measurements began in 1979. September Arctic sea ice extent has declined by over 40%.
• The Greenland ice sheet is losing approximately 280 billion tonnes of ice per year (2002–2020 average).
• The Antarctic ice sheet is losing approximately 150 billion tonnes of ice per year.
• Mountain glaciers worldwide are retreating. The World Glacier Monitoring Service reports that glaciers lost more ice between 2000 and 2020 than in the entire 20th century.

Sea-Level Rise

• Global mean sea level has risen by approximately 20 cm since 1900.
• The rate of rise has accelerated from 1.4 mm per year (1901–1990) to 3.6 mm per year (2006–2018).
• Sea-level rise is caused by two factors: thermal expansion (warmer water expands) and the melting of land-based ice (glaciers and ice sheets).

Atmospheric CO₂ Concentration

• Pre-industrial CO₂ levels were approximately 280 parts per million (ppm).
• Current CO₂ levels have exceeded 420 ppm — the highest in at least 800,000 years (based on ice core evidence).
• The increase in CO₂ closely matches the increase in fossil fuel burning since the Industrial Revolution.

Exam Tip: When presenting evidence for climate change in an exam, organise your answer around different types of evidence (temperature, ice, sea level, CO₂). For each one, give specific data — examiners reward precise figures.

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Impacts of Climate Change

Impacts on the Physical Environment