The temperature of the Earth, as well as the temperature of other planets, depends strongly on the composition of the atmosphere and how significant the effects of the greenhouse effect are.

On Earth, the temperature is kept at a comfortable level since the atmosphere traps some of the radiant heat from the Sun, warming the surface and sustaining life. This trapping is done by greenhouse gases in our atmosphere, which absorbs some infrared heat radiation and reradiates some to the surface of the Earth to warm it.[1] The warming influence on the Earth is crucial to the existence of life on Earth. Without the influence of the greenhouse effect on our planet, the average surface temperature would be 255 Kelvin - which can also be expressed as -18°C or 0°F.[1] If this were the case, water on Earth would freeze and life as we know it would not exist. This is a significant temperature drop in comparison to the approximately 15°C average temperature on the Earth with the greenhouse effect.[2]

The temperature for the Earth if the greenhouse effect is not taken into account can be derived from the expression called the Stefan-Boltzmann law. By accounting for the surface area of the Earth and the power from the Sun reaching the Earth, the equation is as follows:[3]

[math]S = e \sigma T^4[/math]


  • [math]S[/math] is the amount of sunlight that a square meter of Earth's surface absorbs on average. This takes the solar constant, divides by four (to spread it evenly over both latitudes and the day/night cycle) and then accounts for 30% of light being reflected into space. Giving:[math]\frac{1364}{4} \frac{W}{m^2}\times 0.7=238.7\frac{W}{m^2}[/math]
  • [math]e[/math] is the emissivity of an object, generally set to 1 for an ideal radiator
  • [math] \sigma [/math] is the Stefan-Boltzmann constant
  • [math] T [/math] is the temperature of the Earth, in Kelvin

With accepted values in this equation, the theoretical average temperature of the Earth is:

[math] 238.7 \frac{W}{m^2} = (5.67 \times 10^{-8} \frac{W}{m^2K^4}) T^4[/math]

[math] T = (4.22 \times 10^9 K^4)^{1/4} = 255 K= -18[/math]°C

For Further Reading

For further information please see the related pages below:


  1. 1.0 1.1 NASA's Cosmos. (May 7, 2015). Heating by the Greenhouse Effect [Online]. Available:
  2. The Encyclopedia of Earth. (May 7, 2015). Greenhouse Effect [Online]. Available:
  3. R. Wolfson. (May 7, 2015). Environment and Climate, 2nd ed. New York, U.S.A. Norton, 2012, pp. 320-322