Earth average temperature

Figure 1. Average temperature profile of air above the earth s surface.

The role of atmospheric CO2 in the greenhouse effect. Carbon dioxide is transparent to incoming sunlight, but it absorbs and re-emits a significant amount of the infrared radiation emitted by the Earth. This alters Earth s energy balance, raising its average temperature. 

Since the earth has temperature, it emits radiant energy called thermal radiation or planetary infrared radiation. Measurements by satellites show an average radiant emission from the earth of about 240 watts per square meter. This is equivalent to the radiation that a black body would emit if its temperature is at -19°C (-3°F). This is also the same energy rate as the solar constant averaged over the earth s surface minus the 30% reflected radiation. This shows that the amount of radiation emitted by the earth is closely balanced by the amount of solar energy absorbed and since the earth is in this state of balance, its temperature will change relatively slowly from year to year. 

Most climate models show a climate in stable equilibrium. If the 1900 condition of 300 parts per million doubles to 600 ppm, most three-dimensional models indicate an equilibrium with an average surface temperature warming of 3.5° to 5°C (5.6° to 9°F). If the carbon dioxide content of the atmosphere doubled in one month, the earth s temperature would not reach its new equilibrium value for a century or more. 

The increased use of hydrocarbon fuels in the last five decades is slowly increasing the concentration of carbon dioxide in the atmosphere, which produces more carbonic acid, leading to an imbalance in the natural carbon dioxide content of the atmosphere, which, in turn, leads to more acidity in the rain. In addition, there is a greenhouse effect, and the average temperature of the Earth may be increasing. 

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