The sun and earth constitute an energy system. The sun produces energy, approximately 4*10^26 watts, of which the earth receives a portion, approximately 1.7*10^17 watts.
Of the solar energy coming to earth, a proportion is reflected, a proportion is absorbed by the atmosphere and a proportion is absorbed by the earth. The earth, like all matter, radiates energy proportional to (the 4th power of) its temperature (Kelvin). A proportion of the radiated energy is absorbed by the atmosphere and a proportion of the radiated energy escapes to space. This is frequently called the global energy balance . For more information on this subject see Earth's Annual Global Mean Energy Budget.
If the atmosphere were magically removed from the above system, the equilibrium temperature at the earth surface would be approximately -15C. In fact the measured temperature at the earth surface is approximately +15C. The approximately 30 degree difference is due to what is called the natural greenhouse effect.
If one looks at the range of temperature variations over the
lifetime of the planet, there have been many changes.
See, for example:
There are several factors which affect the average surface temperature.
Among these
factors
are:
In historical time, it appears that humans have begun to affect the average surface temperature primarily via the concentration of green house gases in the atmosphere. The recent temperature record shows:
The relevant questions are:
While you consider these questions, you might like to keep in mind, that if you come to the conclusion humans must reduce the concentration of green house gases in the atmosphere, there is a significant fossil fuel industry and lobby which stands to lose greatly by that decision. A consideration of the scope of the effort to utilize alternative energy sources may be relevant.
Skepticism is a good thing. Science thrives in an environment of challenge and question. A refusal to acknowledge some data and a narrow minded self serving interpretation of other data, however, does credit to no one.
The Climate Change issue which many now regard as a fringe concern
may be considered by future generations to have been pivotal.
Consider well.
Last modified December 31, 2007
