Monday, October 01, 2007

The "greenhouse effect" misnomer

A reader writes:
...One thing that I find particularly grating is the continuous use of the expression "Greenhouse Effect" to describe the additional warming of the atmosphere produced by infrared radiation absorbing and reflecting gases such as H2O vapor, CO2, methane, etc. It is a minor quibble as things get misnamed all the time but I think it has some significance. The point being that the warming of greenhouses has nothing to do with glass being an infrared absorber and reflector as demonstrated by a simple and elegant experiment by Wood in the early 20th century. More information is in the enclosed PDF file.
(See Section 2.5 "Experiment by Wood" beginning on page 32 here.)

More information on real greenhouses is here:
The term 'greenhouse effect' originally came from the greenhouses used for gardening, but it is a misnomer since greenhouses operate differently [10] [11]. A greenhouse is built of glass; it heats up primarily because the Sun warms the ground inside it, which warms the air near the ground, and this air is prevented from rising and flowing away. The warming inside a greenhouse thus occurs by suppressing convection and turbulent mixing. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature will drop considerably. It has also been demonstrated experimentally (Wood, 1909): a "greenhouse" built of rock salt (which is transparent to IR) heats up just as one built of glass does. Greenhouses thus work primarily by preventing convection; the atmospheric greenhouse effect however reduces radiation loss, not convection. It is quite common, however, to find sources (e.g., [12] [13]) that make the "greenhouse" analogy.

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