My home country of South Africa has been struggling with power for the past decade. Every day a third of the day is spent without power. Being without power like that, makes you appreciate how much it forms the bedrock of our society. Imagine doing anything in your day without some form of power or power system. Electrification has been with us so long, that all other modern systems, from water, to gas, to food, depend on its ready availability for its continued existence.
Electrification is changing with renewables, but fundamentally the issues of demand and supply mismatch will mean that renewables will never be the sole solution - overcast New England is colder and therefore needs more power than sunny Texas - with transmission lines being only a temporary stopgap to that issue. Therefore I think that coal and gas power will still be with us for the time being. Nuclear is a cleaner option, but the associated capital costs are so vast that it is inevitably a loss making operation in the short term, and so coal and gas power plants will still be run and built. Fusion is looking promising, with many startups working on some form of it, but it’ll still take many years before it comes to fruition. Therefore, in the year 2084, while there will be more widespread use of solar and wind power, especially when it comes to transport, gas will still continue to form the underpinnings of the electrical system, with coal as an emergency stop gap. The shale revolution in the US means too that natural gas will continue to be produced in massive amounts, and so this will still be economical for decades to come.
Of course, that probably means that climate change will probably be inevitable, and so in the year 2084, there will be many adaptions to live with the results. Dykes will hold back the sea, houses will be redesigned to fit the changing climate, and people will move. I think that though, fundamentally the number of humans won’t be affected. It’ll be just like now, when millions already live in dangerous environments without extinction, just that the dangerous environments will have shifted.
It’ll be a familiar world in that respect, only with some of the parameters changed.