A greenhouse works by allowing the heat from the Sun to go straight in through its glass windows. Once inside this heat energy is then trapped by the glass. This makes the greenhouse get hotter.
You can see this in more detail in this demo.
A similar thing can happen to some planets. Instead of glass, some gases in the atmosphere can trap the Sun's heat energy. These gases stop the heat from escaping back into space. These are known as Greenhouse Gases. The more of them there are in the atmosphere, the stronger the greenhouse effect is.
There are three main Greenhouse Gases on Earth. They are methane, water vapour and carbon dioxide (CO2). They occur naturally, but humans can raise their levels.
- Methane is produced when plants decompose. It is also produced by rice and cattle farming, and coal mining.
- Water vapour is produced when water from oceans and lakes evaporates. It is also produced by burning some fuels.
- CO2 is produced when plants and animals respire. It is also produced during forest fires and volcanoes. A lot of it is produced when we burn fossil fuels or make cement.
Sometimes humans cut down forests to clear the land for farming. When we do this, we stop those trees from removing CO2 from the atmosphere. This means more CO2 ends up in the atmosphere.
If the amount of greenhouse gases increase, so does the average temperature on Earth. This leads to climate change. One effect of climate change is the melting of polar ice.
Venus has a much stronger greenhouse effect than Earth. The temperature on Venus is around 400 °C higher than on Earth. The greenhouse effect makes the surface of Venus is even hotter than the surface of Mercury. Although Mercury is closer to the Sun.