The Earth is unique to our solar system: it
can sustain life.
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.
SeaWiFS Teacher's Guide and Activities