Well...I have some reasoning to think it is BS. I guess I might as explain it.
The IPCC states that we are going to raise the earths temperatures by 1.4 degrees C in the next 100 years. I think natural events cause far more impact than can be determined by this panel. For instance, after Mount Pinatubo erupted in 1991, global temperatures fell by 0.5 C. The ozone hole grew much larger. In 1883, Krakatoa erupted and caused global temperatures to fall by 1.2 C. My point is that two volcanoes altered the global temperatures by a modest amount.
In the 1970s people were worried about slipping into another ice age. Temperatures in the US now are finally back up to the peaks they were at in the 1930s (as shown by the US temperature data on the NASA website listed earlier). If you look at all the temperature data, the year to year variation is more than the overall trend.
Looking at natural cycles we are close to 400 years from another ice age. The global temperatures always peak right before this. Anyways...I still maintain that human induced global warming is BS. We do have an effect, but far much less than Al Gore would have us believe.