3.3 Greenhouse gases

Greenhouse gases tutorial

  1. What are greenhouse gases?

Many of the gases that occur in the Earth's atmosphere are greenhouse gases. They include carbon dioxide, methane and water vapour. Greenhouse gases occur both naturally and due to human activities.

A greenhouse gas is one which traps heat radiated from the surface of the earth. The term comes from the fact that these gases act like a greenhouse to limit the loss of heat from a system*. The diagram below shows the greenhouse effect, the way in which these gases help warm the Earth.

Diagram of the greenhouse gas effect

The steps are:


Without a layer of greenhouse gases the earth would experience huge extremes of temperature and would be a hostile place to live.


* In fact the term 'greenhouse effect' is a little misleading because greenhouses warm up primarily through the prevention of convective cooling by the glass (airflow is reduced), whereas greenhouse gases trap radiated heat from the earth's surface and re-radiate it.