As pointed out by Lionel Dricot at http://ploum.net/post/the-cost-of-being-convinced, there is a cost of changing your position. A large number of climate deniers have invested themselves in the position they have taken, and unless they can find a benefit to changing their position that outweighs the investment they have made, they are likely to stand firm in their state of denial.
Potentially a far more useful technique, than bashing them over the head with the facts, is to start by having them review the facts surrounding the level of CO2 in the atmosphere, and then ask them to provide proposals as to why those levels have changed in the timeframe they have. That engages them in the process of actually doing science, as once they have proposed a hypothesis as to what may be causing an increase in CO2, those hypotheses can be tested. (I.e. it's the destruction of the rainforest - what does satellite data show about the circulation of O2 generated in the rainforest? It tends to stay in the area of the rainforests. Volcanoes emit CO2! Have we seen a tremendous increase in volcanic activity in the past century? No. Etc.) Start getting them to invest in looking at possibilities that can be tested, rather than having them try to change their minds based on decisions they have invested in.
Nah, it probably won't work, but it seems to me to be better than trying to sit and debate the topic with people who've come to the table already decided that no matter what the logic of proof that's provided, they are not going to change their position.