It is a scientific fact that CO2 absorbs infrared radiation at wavelengths of 2.7, 4.3, and 14.77 microns. An increase in CO2 in the atmosphere will therefore tend to increase the temperature of the atmosphere. Most everyone agrees with that. The question about Apocalyptic Anthropogenic Global Warming (AGW) revolves around how robust the Earth's climate system is. The proponents of Apocalyptic AGW think that the system is not robust, and that all feedbacks are positive and none are negative, so a small temperature increase will lead to runaway increasing temperature. The skeptics think that not all feedbacks are positive, and the climate system is robust. There is a lot history going back millions of years that support the robust climate hypothesis (and proponents of AGW know that, which is why they have taken such pains to modify the record). Here is a good discussion of the history of Earth's climate.