Well if you accept the physics of increasing CO2 in the air.  Then you need to look at the chemistry of burning the gigantic quantities of mostly solid carbon in Coal C + O2 in the air =&#62; an even larger quantity of CO2 by volume in the air.  Some basic math on the mass of Carbon released from Coal + Hydrocarbons (which mostly end up as CO2 and H20 after complete combustion) you find that tracks with the increase of CO2 in the air.<p>Like most complex scientific theories there are several steps of logic involved.  And while a few groups agree on which specific steps break the chain a slightly larger but still small group of people can agree that it's broken.