There was an interesting article on LiveScience.com today, 8 Ways Global Warming Is Already Changing the World. Of course, there are many more than just eight ways things are changing, but its still an interesting piece.
Global warming deniers will tell you that these changes are isolated, but they can't explain how it is they are world-wide in nature. They will tell you these are only natural variations, but they can't explain how there are no natural causes that can account for them. Most importantly, the deniers cannot explain how it is so many things are changing, all at the same time and on a world-wide basis.
The secret to debunking global warming deniers is to make them give you details and to look up the science yourself. Without exception, none of the claims of deniers can withstand scrutiny.
And, I am completely serious. Not a single denier claim is valid.