Guys,
Please don't take this as my being snotty or anything like that -- but have you guys actually read any of the science behind global warming? The evidence really is quite conclusive. There are literally hundreds of scientific papers that makes the case behind CO2 and global warming. Sure, methane is a contributor, too as well as many other factors. But, all in all, the evidence is very string that it is man-made.
http

/earthguide.ucsd.edu/globalchange/global_warming/03.html
The above link is a good introduction that discusses the facts as we know them. Sure, there is a lot more to learn, but the evidence is there. Denying it won't do us any good.