Rigorous standards of evidence means reproducible experiments and accurate, verifiable predictions. None of which, to date, AGW proponents have been able to produce. Until that happens, we have to entertain the possibility of different explanations for variations in climate patterns.
Patterns that, according to the scientific record, have gone through many, much more drastic, changes since well before human and animal life existed on this planet.
Human produced carbon emissions could be having an effect on our climate. However, until that is proved to a certainty, by the reproducible experiments and verifiable predictions mentioned above, we shouldn't go destroying our economy and expanding government powers in a desperate attempt to head off something we don't fully understand nor know how to control.
All actions of man (particularly the large-scale ones) have unintended consequences. Flood a desert, destroy an ecosystem. Build a dam and cause widespread deforestation. End hunger and disease, cause an overpopulation problem, The process used for creating artificial fertilizers also allowed Germany to continue to produce ammunition and allowed the First World War to go on three years longer than it should have, at the cost of millions of lives.