the Greenhouse Effect Happens
its name from the heat build-up characteristic in greenhouses
during the day. Solar radiation from the sun is composed
of relatively short wavelength radiation, with about 10% being
ultraviolet (UV), about 40% being visible and about 50% being
short wavelength near infrared (IR). This radiation is
absorbed by the objects of the earth or inside the greenhouse
and the radiant energy is converted into heat energy and the
objects increase in temperature. The objects will then
begin cooling themselves by conduction, convection and radiation.
The radiation emitted (re-radiated) is long wavelength
IR. The atmosphere and greenhouse glass are opaque to the
long wavelength IR. In the atmosphere, carbon dioxide gas
and water vapor absorb the long wavelength IR, which is then
radiated back down, thus trapping the long wavelength IR in the
earth's atmospheric environment. In the greenhouse, the
glass bounces the long wavelength IR back down. This trapped
long wavelength IR is absorbed by objects, which causes further
heating, and the cycle continues. Thus, the earth and greenhouse
act as solar collectors.
Dioxide Emissions and Global Warming
increased carbon dioxide emissions from burning fossil fuels
(and to a lesser degree massive forest and oil field fires)
have caused the level of carbon dioxide in the atmosphere to
increase from about 300 ppm to 350 ppm over the last century.
This is "fueling" speculation of global warming due to an enhanced
greenhouse effect. Is it real? Time will tell!