From the intro:
"While current analyses are unable to predict with confidence the timing, magnitude, or regional distribution of climate change, the best scientific information indicates that if greenhouse gas concentrations continue to increase, changes are likely to occur.
The U.S. National Research Council has cautioned, however, that “because there is considerable uncertainty in current understanding of how the climate system varies naturally and reacts to emissions of greenhouse gases and aerosols, current estimates of the magnitude of future warmings should be regarded as tentative and subject to future adjustments (either upward or downward).”
Moreover, there is perhaps even greater uncertainty regarding the social, environmental, and economic consequences of changes in climate. "
Sure, but they'd have to increase an impossibly large amount in an impossibly short time.
I am 100% certain that changes will occur even if greenhouse gas concentrations stay exactly the same.