Earlier quoted context omitted.
If we continued to build nuclear rather than retire them then we wouldn't have any issues today except cars and air. What do you mean "not most cost efficient", there are no other options we know of today. They are all based on future tech we don't have, like being able to store wind or solar etc. Do you really want to bet the future of earth on the chance that we find a solution to those problems before climate chan…
We have the technology to store wind and solar: batteries for very short durations, electrolysis (optionally followed by a Sabatier reaction to make Methane) for longer duration. Both are quite expensive, but so is nuclear. I don't know which option is cheaper overall.
The capital cost of any battery, flywheel or pumped storage is higher than the $30-50/MWh energy of a nuclear plant, without even having built any PV or wind generation.