"A big nuclear accident can potentially wipe us human out!"
This is highly unlikely bordering on technically impossible (I am assuming you are talking about nuclear power, not bombs). You can work out the worst case scenario and it will still have only regional impact. Small nuclear accidents can happen, but will become less likely as people learn.
Lets compare possibilities of a global wipe-out from fossil fuels and nuclear.
Non-withstanding the gradual deterioration of our planet from global warming, it is also possible that we will be wiped out almost instantaneously in a relatively near term, e.g. couple of hundred years. (I wouldn't call it "likely", but given the stakes, we should not be playing with matches either).
The clathrate gun hypothesis suggests that rises in sea temperatures can trigger the sudden release of methane from methane clathrate compounds buried in seabeds and permafrost.
The last gun is thought to have caused Permian-Triassic extinction event where up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct.
So, sum it up: CO2 is definitely bad (but delegates problems to future generations) and possibly catastrophic; Nuclear can be bad if we are not careful; Solar and other renewables are good, but nowhere near ready to replace the above for another couple of decades at least; No power at all is VERY bad
Smarter governments (this clearly excludes Australia) will chose nuclear and investment in renewables.
