People can stop it. Each day, the typical American puts carbon in the air simply by waking to an electric alarm clock, switching on a coffee maker and turning up the heat. During the course of a year, each American on average puts more than 5 tons of carbon out there, not counting what he or she exhales. That's the most per capita of any nation on Earth. In the form of diamonds, this represents enough carbon to fill nearly two dozen 20-gallon garbage cans.
Humans produce it as carbon dioxide, the most abundant heat-trapping greenhouse gas.
It would be better if we could see it. Global view Rising levels of carbon dioxide have become so acute that hundreds of scientists earlier this year said global warming is a clear and present danger. The United Nations-sponsored Intergovernmental Panel on Climate Change reported that the world's average temperature, which rose about 1 degree Fahrenheit in the 20th century, could rise between 2.5 and 10.4 degrees F in this century. A growing majority of scientists say most of the warming probably comes from human-caused releases of carbon dioxide, now more abundant in the atmosphere than at any other time in the past 420,000 years. Along with gases such as methane and nitrous oxide, the gas lets solar energy reach the Earth but traps the energy as it later rises in the form of heat.