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.