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The temperature on Venus is so high because the carbon dioxide atmosphere or sulfuric acid clouds hold(s) in the heat.

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The atmosphere of Venus is heated primarily by carbon dioxide which makes up about 95 percent of its composition. The density of Venusís atmosphere is about 90 times that of the Earthís air density. The artificial elevation of temperature by a planetís atmosphere is called the greenhouse effect. It is the major factor in Earthís emerging global warming crisis. The reason for Venusís extreme temperature can be compared to the heat experienced when a person enters a closed car on a hot summerís day. Sunlight streams through the windows of the car and is absorbed by the seats and other interior objects. The seats warm up, radiating their heat which then warms the air inside of the car. The warmer air transfers its energy through the carís windows more slowly than the heat that is being generated by sunlight coming through the windows. The interior of the car becomes warmer than the outside air temperature. On Venus because of its thick sulfuric acid haze layers, only a very small amount of solar energy reaches the surface of the planet. This energy is absorbed by the ground and is radiated back as heat, which is then absorbed by Venusís carbon dioxide atmosphere or reflected back towards the surface of Venus by its sulfuric acid clouds.

Venus with Clouds
Venus' clouds of sulfuric acid, and its atmosphere of almost pure carbon dioxide, trap the sun's heat.

Venus with Clouds
In a greenhouse, light from the sun can easily get in through the windows. The sunlight is absorbed by the flower beds and some of this energy is changed into heat. The heat warms the air, but the warm air has a greater difficulty in transmitting its energy back through the glass. The heat builds inside of the greenhouse causing it to be warmer than the air outside. This is called the Greenhouse effect.

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