What about the way the information is often presented to the average person as a justification for policy change. How often does the average person encounter information about global warming devoid of an attempt to change policy in relation to the information? That alone would cause reason for a person doubt the authenticity of the information since the source is seen as biased. Add in how badly news organizations butcher the actual science, and there is plenty of room for doubt that then can be exploited by those who specifically seek to do so.