Until quite recently, there was considerable debate as to whether global warming is occurring or not. However, this appears to be largely settled.
An ongoing debate involves the extent to which global warming is caused by human actions, such as the extensive use of fossil fuels. This debate mostly occurs among the public, whereas the issue amongst climate scientists is mostly settled in favor of the anthropogenic hypothesis.
Sciforums debates on global warming
Global warming 
Reality Check: Global Warming is a Serious Problem 
The Great Global Warming Swindle 
Global Warming, Spin and Media 
Global Warming: The Greatest Hoax in the History of Science 
Reality and denialism: Global Warming 
The responsibility of global warming