Unproven relationships among problems

In the absence of adequate research on problems and associated phenomena, it can easily be assumed that there is no causal relationship between certain problems (eg smoking and lung cancer, acid rain and forest decline, carbon dioxide emission and global warming). It is especially convenient in a political context to rely on the argument that there is "no proven link". Recognition of the existence of any such link may be delayed for years until no reputable specialists can be found to question the arguments of those who initially demonstrated the possibility of such a link.