There is no contradiction other than with the reframing that global warming deniers use to communicate with their less educated members. Anybody with 2 working neurons realises that fit for life and fit for human are 2 distinct concept, otherwise they can jump in the thriving ocean and live like a fish.
In general actual debate are around either if global warming happens or not ( which is pretty much settled ), if CO2 is the main factor or not ( also pretty much settled, although some other gas are investigated ), the actual effect on human ( pretty much settled that it is going to cause grief, the debate is around knowing if that affect us in the first world yes or no and the timescale )
The bitter debates (the actual contradictions) are around what to do without destroying your economy, not sacrifying your economy for a problem that will not really affect you and position your economy to profit from it.
Starting early in Earth's history more CO2 got dissolved in the primordial ocean and locked down than what got released by other processes such as volcanism or plate tectonics.
All that carbon in coal seams used to be in the air. Not many people know the atmospheric CO2 level during most of Earth's history was well over 1000 ppm, and commonly around 3000 ppm.
http://www.geocraft.com/WVFossils/Carboniferous_climate.html
Interesting contradiction isn't it? Our slowly rising atmospheric CO2 level today is just reaching 400 ppm, and this is claimed by some to be disastrous. Yet it has usually been far higher, and Earth thrived in those times.