The "denier" camp? You sound like Groggy when you post things like that.If had it been false someone in the denier camp would have said so and why they said so. Have anyone, besides yourself said so?
A person who says that we don't have the evidence to know whether man-made carbon dioxide emissions affect the climate is not a "denier."
In any event, I don't know about Powell's most recent pie chart, but previous versions certainly have been challenged:
http://www.populartechnology.net/2013/04/13950-meaningless-search-results.html
In my own words, I would say the problem with asking whether or not it is "false" is that it's the wrong question. The pie chart may be a factually correct representation of his interpretation of the papers, but it is exceptionally misleading.
It says two papers "reject" man-made global warming, and says nothing about the rest -- other than to cite the total number of papers he looked at. Did most of the remaining ones support global warming? Were they neutral? Did they even address global warming (Powell's catch phrases are quite broad)? We have no idea.
The pie chart tells you absolutely nothing.
But it creates the dishonest illusion of an overwhelming "consensus," when in fact the majority of papers may not have expressed a view one way or the other (that was certainly the case with Cook).
It's not technically false. It is probably more accurate to describe it as pretty much the same thing as a lie by omission. It is designed in such a way as to lead people to extremely false conclusions.
It's utterly worthless as research. Its sole purpose is to mislead.
And it undermines the argument that people who believe in AGW are focused on science. It is political propaganda of the worst kind.