The best answer to what the real science says about the future of global climate is basicly "we don't really know yet".
From my understanding it's more like "We have a clear indication that ..." meaning that while they don't really know everything since they're dealing with complex systems their current understanding points to bad things.
Then you have the politicians who have to cry wolf to get anything done.
There is a clear indication that the climate is trending warmer, and has been since the end of the 'little ice age'. There is also a clear indication that CO2 is a greenhouse gas. There is not a clear connection between the two. The environment is a very complex system and the concentration of CO2 a very small part of it. Both the climate and the level of atmospheric CO2 are in constant flux over millienia, but the CO2 concentration tends to be a
lagging indicator; implying that the increases of CO2 in the atmosphere are an effect of a warming global climate, not a cause. Although it's certainly possible that CO2 is, itself, a feedback loop. There is no indication, nor any logical reason to assume, that even a tripling of the amount of carbon in the air would result in a catastrophic degree of climate change. Even a 4 degree global change would take at least a century to materialize.