Welcome to the Slate Green Challenge: Your eight-week carbon diet.

By Meaghan O'Neill and treehugger.com
Posted Monday, Oct. 23, 2006, at 11:56 AM ET

There's no longer any real doubt about it: Global warming is happening. The average temperature of the Earth's surface has risen about 1 degree Fahrenheit over the past hundred years, and overwhelming evidence suggests that most of the increase is due to greenhouse gases, particularly carbon dioxide released by humans. Though a 1-degree increase might not seem like much, even a small rise in global temperature significantly changes the climate, potentially resulting in major storms and droughts, disruption of the food supply, and the catastrophic spread of disease.

Human carbon-dioxide emissions come mainly from two sources: burning fossil fuels and changes in land use, such as deforestation. Americans are the climate's worst enemy. On average, each of us is responsible for about 22 tons of carbon-dioxide emissions every year, according to the United Nations, compared with an average of six tons per person throughout the rest of the world. That means the typical U.S citizen emits the equivalent of four cars.