Do deniers believe that scientists simply assume humans are causing global warming?

"What we argue is that because many of such natural warm periods remain unexplained or less than fully explained, we cannot simply assume that the present warmth was caused by CO2 or by man."

http://answers.yahoo.com/question/index;...

Is this their extent of their knowledge of climate science?
Update: Spammer WhyTaxCarbon illustrates the motivation for global warming denial - politics.
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