There is some dispute, as you obviously well know, about how much human generated greenhouse gases affect the environment, so I'll leave that to others.
But even if one were to accept that human generated greenhouse gases will contribute to global warning, the question still remains what our best response should be. Economist Bjorn Lomborg discusses how top economists from around the world met for a conference discussing various world problems, what responses we could make and then prioritized things to see where we would get the most bang for the buck. With respect to climate change, they used the numbers given by the mainstream climatologists. Interestingly, reducing greenhouse gases came in last place as to the best ways to spend the money world governments are likely to allocate. He gives a lot more detail in this short talk you can watch online:
http://www.ted.com/talks/bjorn_lomborg_sets_global_priorities.html
Another issue is that the earth's weather has changed significantly over time even before man ever came on the picture, and there is no reason to think that variability would not continue regardless of what steps man takes to minimize his impact upon the weather. For instance a number of scientists are worrying that a much bigger factor in our weather could be setting us up for yet another catastrophic shift in our weather quite independent of global warming. Here's one such story that discusses some of what other publications and the scientists they've been interviewing & quoting have been writing about this phenomenon:
Magnetic Polar Shifts Causing Massive Global Superstorms
Then too, we shouldn't ignore the hypothesis of the Wall Street Journal that we're better off maintaining a healthy economy with the resources to minimize the deaths, injuries and property damage of various catastrophies than in trying toalter our behavior in the hopes in will minimize our impact on the weather, if that in turn cripples our economy and ability to deal with such inevitable tragedies:
The Weather Isn't Getting WeirderGood post, analogous “climate catastrophe” has happened in the middle ages, the 1800’s, the 1930’s and even the 1970’s. Floods will happen so we need dams, not just for hypothetically more rainfall. Storms have always happened and “superstorms” are not really possible due to limits in fluid dynamics.