One of three things must be true.
One: “Renewable” energy sources, wind and solar, are well defined and resolved technologies that are now capable of meeting the lion’s share of our current electricity needs and expanding to all the proportionately larger component of that demand that must result in our transition from fossil fuels. In which case all is well with the world because even selfish market forces would propel any economy toward renewables.
Two: “Renewable” energy sources, are not fully developed technologies and many issues remain unresolved. However eventually, in ten or twenty or thirty years, they will be. For instance we do not have battery technology to support a transition to wind and solar. Also we need considerable advancement in materials research or vast new sources of rare minerals to come anywhere near meeting the demands of transitioning. But these hurdles may be overcome. At which point, eventually, all will be well as these technologies inevitably supplant ones with greater environmental footprints.
Three: “Renewable” technologies never really come up to meeting current generating levels, let alone the vast increases that would be required to supplant fossil fuels. This is entirely possible. There may not be practical batteries better than lithium-ion. There may never be enough rare elements to build all the units. I hope this is not the case. But it may be.
For decades people have been hoping that fusion was just thirty years away. However it is also possible that the €13 billion ITER experiment in France will conclusively show that fusion is not viable. Should the research have a more desirable outcome then it will still be decades before commercial reactors are displacing other electricity sources. We shall see.
And here is the thing. There is a gap. The gap started in 1997 with the signing of the Kyoto Protocol. The day after that we should have been transitioning to the carbon-free sources of energy at our disposal. Twenty two years ago we should have been building nuclear reactors to at the very least fill the decades gap until some unrealized technology could replace them.
Unless you believe in option one, which is discounted by the very researchers working on the problem, we still need to be building nuclear reactors to fill that gap. And that’s assuming it is a gap and the problems of replacement technologies become resolved in coming decades. Which they may not.