absolutely fantastic article at Forbes that describes the differences between warmers and skeptics-
Understanding the Global Warming Debate - Forbes
I highly recommend reading the article
Understanding the Global Warming Debate - Forbes
The IPCC assumed that strong positive feedbacks dominated, and thus arrived at numbers that implied that feedbacks added an additional 2-4 degrees to the 1 degree from CO2 directly. So in the IPCC numbers, at least two thirds of the future warming comes not from the basic greenhouse gas effect but a second independent theory that the Earths climate is dominated by strong positive feedbacks. Other more alarmist scientists have come up with feedback numbers even higher. When Al Gore says that we will see a tipping point where temperatures will run away, he is positing that feedbacks will be nearly infinite (a phenomenon we can hear with loud feedback screeches from a microphone).
But the science of this positive climate feedback theory is far from settled. Just as skeptics are probably wrong to question the basic greenhouse gas effect of CO2, catastrophic global warming advocates are wrong to over-estimate our understanding of these feedbacks. Not only may the feedback number not be high, but it might be negative, as implied by some recent research, which would actually reduce the warming we would see from a doubling of CO2 to less than one degree Celsius. After all, most long-term stable natural systems (and that would certainly describe climate) are dominated by negative rather than positive feedbacks.
I highly recommend reading the article