The problem is, there is great research on warming, there is also bias in research. Majority of scientists have their conclusions before doing research, and often times try to make their data fit their conclusion. This is a problem in almost all research. However, peer review is made just to stop this issue.
Check out Sci Fri podcast from a few weeks ago, they do a great job of explaining this.
Basically, deniers are still idiots. They have a legitimate point about bias in observations, but their bias makes them believe all observed science is wrong, all while disregarding peer review.