The Earth is unique to our solar system: it can sustain life.
Without the Earth's atmosphere,
our planet would become extremely cold and
barren of life. The atmosphere consists of
nitrogen (about 70 percent) and oxygen (about 20
percent). The other ten percent consists mostly of
carbon dioxide, water vapor, and several "trace"
gases such as neon and argon.
Like the glass roof and walls of a greenhouse, the Earth's atmosphere keeps its surface much warmer than it would be without the "greenhouse effect." How? Energy from the sun arrives as short-wavelength radiation (light), while the Earth emits long-wavelengeh (infrared) energy back into space. The hotter an object is, the shorter the wavelength of the radiation it emits. The short-wavelength sunlight easily penetrates the atmosphere and warms the Earth. However some of the long-wavelength energy emitted from the Earth is absorbed by the atmosphere before it escapes into space. Carbon dioxide, water vapor and other gases in the atmosphere are responsible for absorbing escaping long-wavelength energy. Thus, the Earth keeps some of the heat that would otherwise have been lost to space.
The concentration of carbon dioxide in the atmosphere has changed in the past hundred years. Before the Industrial Revolution, carbon dioxide levels stayed nearly stable for thousands of years. Since human beings developed a fossil-fuel- based global economy and lifestyle, the amount of atmospheric carbon dioxide has increased dramatically. This increase means that less long- wavelength energy emitted from the Earth can escape to space. Many scientists believe this can lead to a gradual warming of the Earth, but others believe that different factors counteract this warming effect. For example, cloud cover reflects sunlight before it ever reaches the Earth, thus reducing the amount of sunlight that reaches the Earth's surface. Studying these processes is difficult, because they are complicated. Ocean color information provides one of the many tools scientists use to try to find what changes are occurring, and how they may affect us.
Click here for the most up to date plots of atmospheric CO2.