It's incredibly simple. We can, at will, change how the "single" source of energy is generated. There is no time that is too early to have all energy consolidated to one source.
Not only because the plants that generate the electricity are more efficient and cleaner than everyone burning their own fuel (even when they are gas or coal), but because if we are prepared already, as SOON as we make the change to renewables or nuclear, suddenly everything is more clean.
I don't want to be rude here, but I HAVE to assume fully functioning adults are arguing from bad faith here, rather than "not understanding" this concept.
Don't be coy, tell us why you really don't understand this.