Source: World Resources Institute, 1990

The above graph shows the annual increase in the amount of major greenhouse gases present in the atmosphere.

As is obvious from the graph, people have been releasing more and more greenhouse gases, and therefore contributing at an increasing rate to the greenhouse effect.

Some of the major recent causes of the increase in greenhouse gas emissions are the burning of forest areas, especially in tropical regions, increased fossil fuel consumption and burning, and higher levels of electricity consumption.

As the developing world begins to industrialize, the graph will probably continue rising.  China, for example, has seen rapid economic growth in the last decade, but at the expense of high levels of greenhouse gas emissions.