The Greenhouse Effect

The idea

The atmosphere lets sunlight in and slows heat on the way out. Without that, Earth’s average temperature would be about −18 °C instead of about +15 °C. The greenhouse effect is not the problem — strengthening it is.

graph TD
    SUN["Sunlight, mostly visible"] --> SURF["Earth's surface warms"]
    SURF --> IR["Surface radiates infrared"]
    IR --> GHG["Greenhouse gases absorb infrared"]
    GHG -->|"re-radiated in all directions"| SURF
    GHG --> SPACE["Some escapes to space"]

Why the wavelength matters

Sunlight arrives mostly as visible light, which passes straight through $\mathrm{CO}{}_2$. The warmed surface radiates infrared, which $\mathrm{CO}{}_2$ and $\mathrm{CH}{}_4$ absorb strongly. Energy comes in easily and leaves with difficulty — so it accumulates.

Gas	Main human source	Relative warming per molecule
Carbon dioxide, $\mathrm{CO}{}_2$	Burning fossil fuels	1 (the reference)
Methane, $\mathrm{CH}{}_4$	Livestock, landfills, leaks	~25× over a century
Nitrous oxide, $\mathrm{N}{}_2\mathrm{O}$	Fertiliser	~265×

Methane is far more potent but breaks down within about a decade; $\mathrm{CO}{}_2$ is weaker and lasts for centuries. Both facts matter when choosing what to cut first.

Curriculum connection

B2.6

identify and use various indicators of climate change to describe the impacts of climate change on local and global ecosystems, and analyse how human activities contribute to climate change

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B1.1

assess impacts of climate change on the sustainability of local and global ecosystems, describe local or global initiatives for combatting climate change, and identify solutions to address some of the impacts

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