Cars and sprawling cities affect our air quality. In fact, motor vehicles are the single greatest source of air pollution in cities, which means that we can make a big difference simply by changing a few of our driving habits.
Some gases, such as carbon dioxide, are called 'greenhouse gases' because they absorb infrared radiation emitted by the earth's surface and so keep the planet warmer than it would otherwise be. This is called the 'greenhouse effect', which keeps the earth at a temperature capable of sustaining life.
