This is true when proving (or disproving) a theorem - E=MCsquared, for example. But a dissenting voice in the wilderness does not DISprove that A) the burning of fossil fuels creates polution, and B) this polution is toxic to human life in many forms, and C) many of the byproducts released from the burning of fossil fuels are greenhouse gases, which contribute to the warming of an atmosphere.
"Contributing to" would be the operative "weasel words" in your post.
No "deniers" I know deny
a) that climate changes exist (and how interesting that the climate change folks have changed the terminology from "global warming" to "climate change"--kinda covers all bases for when we head toward a mini-ice age again . . . );
b) that burning fossil fuels contributes to pollution; or that
c) in some measure, burning fossil fuels may be one of the factors post-Industrial Revolution society ought to examine when looking at climate changes.
That said, everything I've read and heard about so-called climate change is based on data
a) that extends no further back than a hundred years or so, an incredibly small slice of time when talking about climate as opposed to weather;
b) that is based largely on predictive models;
c) likely miscalculates or misrepresents the measure of man's (and all those nasty fossil fuels') impact on climate change; and
d) would not be changed by wiping man (and all those nasty fossil fuels) off the planet anyway.
I was raised from a pup to conserve natural resources and have always practiced those principles. But I'll be damned if I'm going to have the government sticking its nose into my business, attaching a smart grid to my house and telling me when I can turn certain appliances on or making decisions about what kind of car I can buy when there is nothing "settled" about this science in the first place.
There is no consensus in the data--we're not just talking theory here. Consensus is politics, not science. And the politics have tried to drown out the opposition science. Witness the fellow who tried to confront Gore with facts about the polar bears.