First, I would like to say that I believe global warming is occurring.  The evidence is overwhelming that the Earth has warmed over the past 200 years.  Growing seasons have increased by as much as two to three weeks in many areas, and that could only happen when the temperature rises.

The question is has man caused the warming or is it 100% natural?  I was taught a long time ago never to trust absolutes.  So, I have difficulty believing that man is the only cause of global warming and with the current evidence of increased carbon levels in the atmosphere I have trouble believing that this warming cycle is totally natural.

With this in mind I want to give you some information about non-Earth based factors that could be contributing to global warming.

The sun is the source of essentially all heat in the climate system.  As the Sun ages it gets brighter and its energy output increases slightly.  Thus, as time goes on the Sun will cause the Earth to warm.  This is a very long process, and most likely has only a small effect on the Earth.