page 34


How the Greenhouse Effect Happens
The greenhouse effect gets 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. 

Carbon Dioxide Emissions and Global Warming
The 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!