Earth's Thermal Blanket
🌡️ Earth's Thermal Blanket
Without the greenhouse effect, Earth's average temperature would be about -18°C — a frozen wasteland uninhabitable for most life. Instead, the natural greenhouse effect keeps our planet at a comfortable +15°C. The same process that makes life possible, however, is being enhanced by human activities, trapping more and more heat. Understanding the mechanism behind this effect is one of the most important topics in modern chemistry — and one of the most frequently examined.
Chemistry glossary
- What are the three main greenhouse gases?
- Carbon dioxide (CO₂), methane (CH₄), and water vapour (H₂O)
The natural greenhouse effect has operated throughout Earth's history and is essential for life. Here is the sequence:
Earn the mark scheme marks
🧠 Memory Aid
Greenhouse gases ABSORB infrared radiation and RE-EMIT it back to Earth — these are the two key words for mark schemes
For greenhouse gases: "CO₂, CH₄, H₂O — the 3 C's-M-W" (Carbon dioxide, Methane, Water)
For the mechanism: "Short-wave IN, long-wave ABSORBED and RE-EMITTED back — remember both words for full marks"
Temperature without greenhouse effect: "-18°C = freezing death. With natural effect: +15°C = life. With enhanced effect: above +15°C = problem."
Quick Check: Explain why nitrogen is NOT a greenhouse gas even though it makes up 78% of the atmosphere.
Nitrogen (N₂) does not absorb infrared radiation because of its symmetrical molecular structure. Only molecules like CO₂, CH₄, and H₂O have a structure that allows them to absorb infrared radiation. Greenhouse gases must be able to absorb and re-emit infrared radiation — N₂ cannot do this.
Now try it yourself
Quiz · Question 1 of 25
Which of these gases is NOT a greenhouse gas?
Tap an answer to check it
This topic in real past papers
Every real exam question we've found on greenhouse effect, with a full worked answer.