Home Discussion Forum The sun is the ultimate source of energy in the earth system.?

The sun is the ultimate source of energy in the earth system.?

The sun is the ultimate source of energy in the earth system, and yet the earth’s atmosphere is not heated by the sun. Explain this statement, detailing the role that carbon dioxide plays in this seeming paradox. How does the way in which the earth system is heated relate to the vertical temperature profile of the atmosphere?


  1. The sun is the major of the two sources of energy on earth (the other being nuclear decay).
    Light comes in from the sun in a broad spectrum of electromagnetic radiation. Most are reflected or absorbed, heating the atmosphere (sorry, truth hurts). Many, especially in the visible light range, pass through the atmosphere and heat the earth underneath (the air is mostly clear to the visible spectrum).
    Carbon dioxide is opaque to certain limited frequencies of infrared. (water is more opaque, but why confuse things?). When the earth heats, it radiates infrared, which is absorbed or reflected back if the ray happens to hit a carbon dioxide molecule on the way out. Otherwise, it passes out to outer space.
    To deal with the vertical temperature profile of the atmosphere, one has to know what it is, and compensate for the adiabatic expansion of gasses to calculate “heat” as opposed to “temperature.” One would predict on the model just given that it would be warmest nearest the earth (heat) gradually cooling until the upper atmosphere, where it would be warmed again from the slamming of high energy particles from mostly the sun against the air molecules.

  2. Charles G has a good answer. Also consider that the sun’s energy arrives at earth as photons of pure white light (a mixture of all the colors) that can pass through the vacuum of space and even clear air without being absorbed. When the photons strike matter (the ground) some are reflected but most are absorbed and interact with the electrons orbiting atoms and molecules in the ground. This heats the ground and the air just above the ground that rises and is replaced by cooler air.
    The temperature of the air depends upon how much heat energy it has received which is exhibited by the average velocity (kinetic energy) of individual gas molecules. At sea level the atmospheric pressure is maximum (with the full weight of the air column above pressing down). As you gain elevation there is less air above and the pressure is reduced and the air is less dense. Therefore, thermal energy is less concentrated and the temperature is reduced.


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