Counter like this. Fuel use is all cost per watt and how usable it is. Coal is cheap but no good in cars so it went to power plants. It is the cheapest things around. Nuclear is nice and all but costs more. We don’t see much nuclear because the cost is high. There are perfectly good plans laying around for things like space based power arrays beaming energy to earth. Decades old technology. The only reason it has not been done yet is all cost. So far it is about twice as expensive as nuclear. If the cost of energy goes up there are technologies, like that one, just waiting to be used. Same with oil running out. There are other things that will do the job but they cost more. When the price goes up high enough those things will be brought out. Engineers are smart. Give them a problem and they will solve it. Most of the problems around power are already solved and solved and solved again and the fluctuations of the market dictate what solution we use. No fluctuation will make the problem explode. There are a zillion and 1 ways to make power. There are only so many ways to make it cheap right now. When one way fails us the industrial and intellectual might of the USA will fall on the next best way and that method will come into it’s own. Your hear lots about ‘this new discovery might be the wave of the future’ all the time and then, nothing. Those things get put in the shelf because we don’t NEED them yet. And until the oil goes sky high and or runs out we will not need them. The fact of the mater is that any one with a machineshop and some smarts can make power generating devices of all sorts. Google homemade wind and water turbines sometime. It is really easy. The tides for example are still a vast untaped power source. It is just that until current methods of generating power are no longer workable some things that require a lot of startup effort, like tide power, will never be used.
That or you can just point out that Korea and other places in the far east have WAY higher pop density and they are doing just fine. Or that first world countries have just about all started to level off or decline in their birth rates. Self correcting problem.
Engineers are smart. Give them a problem and they will solve it. That was my biggest point. ;-) But hey, if the argument comes up again, maybe I'll manage to remember some of this advice!
It started with biodiesel, which I think is a cool idea in concept, but if *everyone* was using it, we'd need a lot more crop land and such. It's cheap right now, and a good way of reusing old oil for some of the few who are doing it, but it'd be different if it was the main source of fuel.
And then the argument went downhill from there.