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How does a little CO₂ in the air keep the whole planet warmer?
Greenhouse Effect lab · Last updated: 16 October 2026
You watch sunlight warm the ground and heat rise back towards space, then add carbon dioxide to the air and see what changes. They find out how a gas that makes up a tiny part of the air keeps the whole planet warm, and why adding more of it is changing our climate.
What you'll discover
- Sunlight passes through the air and warms the ground, which then gives off invisible infrared heat.
- Carbon dioxide and water vapour absorb that infrared heat and send part of it back down, keeping Earth warmer.
- Without any greenhouse effect Earth would be frozen, but adding more carbon dioxide makes it warmer still.
The science in plain words
Sunlight is mostly visible light, which passes easily through the air and warms the land and sea. The warm surface then gives off energy as infrared radiation, which we cannot see but can feel as heat. If all that infrared escaped straight to space, Earth's average surface temperature would be about minus 18 °C instead of about 15 °C.
Nitrogen and oxygen make up almost all of the air, and they let infrared pass through. But a few gases, mainly water vapour and carbon dioxide, with methane and others, absorb infrared. Their molecules take in the energy and send it out again in all directions, including back down towards the ground. The surface therefore receives energy from the Sun and from the air above it, and warms up until it loses heat as fast as it gains it. This is the greenhouse effect.
Carbon dioxide is only about 0.04 per cent of the air, but even a small amount has a strong effect, because each molecule is so good at absorbing infrared. Burning coal, oil and gas has raised the amount of carbon dioxide by about half since before the industrial age. More greenhouse gas means less heat escapes, so the planet warms. This extra warming drives climate change: hotter heatwaves, melting ice and rising seas.
Where it fits
- India, NCERT: Goes beyond the NCERT science syllabus for classes 6 to 10; it builds on Class 7 Heat Transfer in Nature.
- United States: Grades 6 to 12
- Next Generation Science Standards: MS-ESS3-5, HS-ESS2-4
Common questions
What is the greenhouse effect in simple words?
The Sun warms Earth's surface, and the surface gives off heat as invisible infrared light. Gases such as carbon dioxide and water vapour absorb some of that heat and send part of it back down, like a blanket. This keeps Earth warm enough for life.
Is the greenhouse effect bad?
The natural greenhouse effect is essential: without it Earth's average temperature would be about minus 18 °C. The problem is the extra greenhouse effect from burning fossil fuels, which adds carbon dioxide to the air, traps more heat and is warming the planet.
How can a small amount of CO2 make such a difference?
Carbon dioxide is only about 0.04 per cent of the air, but nitrogen and oxygen, the main gases, do not absorb infrared at all. Carbon dioxide molecules absorb it very strongly, so even a small amount makes a big difference to how much heat escapes.
Related labs
- Carbon Cycle: When we burn fuel, where does the carbon go? And how much of it stays in the air?
- Heat Transfer: Bridge hot water and cold with a metal bar. Which metal carries heat best?
- Rainbow and Beyond: Slide from ultraviolet through the rainbow to infrared. Which light makes the star glow?
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Try it yourself
The Greenhouse Effect lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.