Global warming is a hotly debated issue, and one that is obviously fraught with many issues dealing with corporate greed, rich and poor nations, scientific method, pig headedness, alarmism and quite possibly some type of theological notion about whether or not man was put here to dominate the globe. And while I am sure that there is a lot of greed and alarmism on the sides of this debate, the key issue to why some people do not believe that global warming is possible is a conceptual, and even metaphysical, issue.
The basic metaphysics followed by the mainstream society both scientific and popular in Western society is so basic that many would deny that it was even such a thing as a metaphysics. This metaphysic basically divides the world into two categories: the atom and the void, or the Agent and the Field. An agent is something that does something, something that can be touched, something that is different than things around it. A field is the set of rules under which things behave. A field can be a geometric field, physical space, or a system of human made laws. To put it in the simplest terms, this is the billiard ball physics view of the world. The balls move from place to place, but the table and the rules don't change.
As a system of metaphysics, this is the culimination of hundreds of years of intellectual developement in society, and is the result of one or two dozen years of developement in an individual. This worldview, where objects and the laws that govern them are clearly set apart, is a great conceptual advance over earlier stages, where universal moral judgements and universal physical laws can not be judged, because there is no universal frame of reference to hang them on.
The problem with this system, and how it relates to global warming, is that in this system, agents can not change the field. The field of laws remains an ever constant guide, in which the agents can effect each other, but the field itself remains inviolate. The agent and the field are are in two metaphysical categories, with the field controlling the agent, and the agent unable to change the field.
So conceptually, the atmosphere of the planet earth is an ever present field, in which we can inhale, exhale, stir up dust and pollute as much as we want without ever changing the field itself. This is of course, not literally true, since the apparent field of the atmosphere is not an absolute field, since it is actually composed of countless seperate agents (molecules). However, as long as the atmosphere remains conceptually a field, the overwhelming legal tradition in the West would be that it can not be changed by agents.
The conservative viewpoint in America, when there was such a thing as an intellectually conservative viewpoint, before conservativism became an excuse for corporate domination, was that the world existed as a neutral worldspace, and that the role of the government inside of that space, was to protect agents from undue influence or threat by other agents. Thus, within the conservative viewpoint, the field remains the same, and the only goal of the government is to stop agents from directly influencing each other. Taking care of the field has no conceptual precedent in Western legal tradition.
Ignoring the entire metaphysical question as to whether agents can indeed disrupt their field; but I should say that the atmosphere can indeed be disrupted by pouring CO2 into it. Whether or not it is actually happening, it can happen. Once this fact is admitted to, the debate can actually proceed using evidence.