The scientists are arguing whether the Earth's climate is warming or cooling, after all there is evince that can be gathered to indicate either effect.
My suspicion is that both effects are happening at the same time, or rather that the soil (earth) and water (oceans) are warming up but the air is cooling down, this effect is caused by human beings, even though they do not understand how they are doing it.

In my opinion, this global change is not caused by the Sun or the greenhouse effect of gasses in the atmosphere.
To understand the cause of the effect, you must first understand several of the laws of physics and chemistry, then apply them on to a global scale.

Some of the pertinent laws are:

Gas laws
http://www.shodor.org/UNChem/advanced/gas/index.html

Thermodynamics
http://www.shodor.org/UNChem/advanced/thermo/index.html

Nuclear fission
http://library.thinkquest.org/17940/texts/fission/fission.html

A thorough understanding of these three subjects would give a good start at understanding the real reason why the climate is changing.

The warming Mars.
http://news.nationalgeographic.com/news/2007/02/070228-mars-warming.html