Without its atmosphere and the greenhouse effect, the average temperature at the surface of the Earth would be zero degrees Fahrenheit. However, too many greenhouse gases can cause the temperature to increase out of control. Such is the case on Venus where greenhouse gases are abundant and the average temperature at the surface is more than 855 degrees Fahrenheit (457 degrees Celsius).
You might hear people talking about the greenhouse effect as if it is a bad thing. It is not a bad thing, but people are concerned because Earth's 'greenhouse' is warming up very rapidly. This is happening because we are currently adding more greenhouse gases to our atmosphere, causing an increased greenhouse effect. The increased greenhouse effect is causing changes in our planet that can affect our lives.
The major Greenhouse Gas, carbon dioxide, emitted naturally and by the burning of fossil fuels, stays in the atmosphere for a long time. Its warming effect occurs even when the sky is clear and dry. Climate scientists are so concerned about carbon dioxide because the more carbon dioxide in the atmosphere, the hotter the earth will become, changing the Earth's climate. The result is called Global Warming because on average, the Earth and our oceans are warming up, and the climate is changing as the carbon dioxide and other greenhouse gases in the atmosphere continue to build up.
Scientists have known and understood this for over 100 years, and it has been confirmed by measurements and in laboratory experiments. There is no doubt about the basic science behind global warming.