The amount of heat energy reaching Earth from the sun can be affected in two ways. One way would be if the suns output were to change and the other would be if Earths position relative to the sun were to change. These changes can be illustrated by visualizing a campfire. As the campfire dies, its output changes, decreasing the energy available to warm the campers. If more logs are added to the fire, the changes in output would increase the energy and the temperature. Now suppose that the campfire is really a propane heater that maintains a constant temperature. Although the temperature remains constant, the camper who forgot to bring a coat has to move closer to the flame in order to get warm.
Another clue in the search for culprits responsible for Earths rising temperatures may be greenhouse gases. Greenhouse gases provide insulation that traps some of the suns heat energy. As the concentration of greenhouse gases increases, the insulation becomes thicker and more of the energy is trapped, resulting in an increase in temperature. This is similar to putting on a heavier coat to get warmer.
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