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A drawing of a portion of the Earth’s surface is shown, with both ocean and continents visible. Different rays such as ultraviolet, visible, and infrared are shown penetrating the atmosphere and impinging on the Earth’s surface. Infrared rays re-emitted by the Earth’s surface are trapped by the atmosphere of the Earth and are scattered back to the Earth.
The greenhouse effect is a name given to the trapping of energy in the Earth’s atmosphere by a process similar to that used in greenhouses. The atmosphere, like window glass, is transparent to incoming visible radiation and most of the Sun’s infrared. These wavelengths are absorbed by the Earth and re-emitted as infrared. Since Earth’s temperature is much lower than that of the Sun, the infrared radiated by the Earth has a much longer wavelength. The atmosphere, like glass, traps these longer infrared rays, keeping the Earth warmer than it would otherwise be. The amount of trapping depends on concentrations of trace gases like carbon dioxide, and a change in the concentration of these gases is believed to affect the Earth’s surface temperature.

The greenhouse effect is also central to the discussion of global warming due to emission of carbon dioxide and methane (and other so-called greenhouse gases) into the Earth’s atmosphere from industrial production and farming. Changes in global climate could lead to more intense storms, precipitation changes (affecting agriculture), reduction in rain forest biodiversity, and rising sea levels.

Heating and cooling are often significant contributors to energy use in individual homes. Current research efforts into developing environmentally friendly homes quite often focus on reducing conventional heating and cooling through better building materials, strategically positioning windows to optimize radiation gain from the Sun, and opening spaces to allow convection. It is possible to build a zero-energy house that allows for comfortable living in most parts of the United States with hot and humid summers and cold winters.

A solar cooker is shown. There is a pot of food inside the solar cooker. The sunlight is incident on the solar cooker and the food is being cooked.
This simple but effective solar cooker uses the greenhouse effect and reflective material to trap and retain solar energy. Made of inexpensive, durable materials, it saves money and labor, and is of particular economic value in energy-poor developing countries. (credit: E.B. Kauai)

Conversely, dark space is very cold, about 3K (− 454º F) size 12{ - "454"°F} {} , so that the Earth radiates energy into the dark sky. Owing to the fact that clouds have lower emissivity than either oceans or land masses, they reflect some of the radiation back to the surface, greatly reducing heat transfer into dark space, just as they greatly reduce heat transfer into the atmosphere during the day. The rate of heat transfer from soil and grasses can be so rapid that frost may occur on clear summer evenings, even in warm latitudes.

What is the change in the rate of the radiated heat by a body at the temperature T 1 = 20º C size 12{T rSub { size 8{1} } ="20"°C} {} compared to when the body is at the temperature T 2 = 40º C ?

The radiated heat is proportional to the fourth power of the absolute temperature . Because T 1 = 293  K size 12{T rSub { size 8{1} } ="313"`K} {} and T 2 = 313  K size 12{T rSub { size 8{2} } ="333"`K} {} , the rate of heat transfer increases by about 30 percent of the original rate.

Career connection: energy conservation consultation

The cost of energy is generally believed to remain very high for the foreseeable future. Thus, passive control of heat loss in both commercial and domestic housing will become increasingly important. Energy consultants measure and analyze the flow of energy into and out of houses and ensure that a healthy exchange of air is maintained inside the house. The job prospects for an energy consultant are strong.

Practice Key Terms 5

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Source:  OpenStax, Physics 105: adventures in physics. OpenStax CNX. Dec 02, 2015 Download for free at http://legacy.cnx.org/content/col11916/1.1
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