Quote from piezoe:
It is not reasonable to question global warming. We are either in a warming period, or we are not according to our adopted criteria and observations.
It is perfectly reasonable, however, to ask what is causing warming or cooling. We know many of the important factors, if not all of them, that contribute to our global environmental temperatures. The question has been asked:" how important is man made emission of CO2 in establishing global temperatures." That's a good question. Some scientists think it has been answered satisfactorily, and others think not; there is a wide range of opinions from relatively important to entirely negligible.
It is unfortunate that many reached early conclusions based on informed guesswork and observations that supported their conclusions. Now we are in the process of becoming better informed, our data is improving, and our understanding of it is improving. We are beginning to recognize that perhaps our earlier conclusions were flawed and we need to revisit them. This has resulted in increasing, not less, uncertainty. Scientists know that any hypothesis can never be shown to be correct with absolute certainty, but that a single inconsistent observation is enough to cause an entire hypothesis to be questioned.
Unfortunately the question of man's contribution to global temperature has ended up in the political arena as well as the scientific one. This has muddied the waters, to the point that some even see the question in terms of political ideology, which from a scientists perspective is incredibly stupid. You can't answer scientific questions with opinion polls, though everyday we see attempts to do just that!