The greenhouse effect is caused by elevated levels of greenhouse gases, such as carbon dioxide, in the Earth's atmosphere. The atmosphere traps radiation from the sun's rays that hit it.
In normal conditions, 30 percent of the radiation is reflected into space. An increased concentration of carbon dioxide disrupts the reflection; too much radiation gets trapped, and the Earth becomes too warm.
The Kyoto Protocol was signed in 1997. All countries that signed it have committed to limit their carbon dioxide emissions to prevent additional increases in the Earth's temperature.Learn more about Atmosphere