Energy is a bigger problem. While we can make energy from renewable sources it is far more expensive (which has ramifications for our entire way of life) and not yet established that we could provide it on the scale necessary to replace our non-renewable sources.
But the biggest problem is resources. Metals, rare earth elements and the like. These are largely irreplaceable in the sense that we can produce so much of them by (typically) digging fairly shallow holes in the ground. We're already going to some fairly inhospitable places to meet our insatiable demand (eg the Arctic in northern Canada and Europe, the Andes).
If we're not careful we may well find our own answer to the Fermi paradox.
Actually, food is the only problem when it comes to whether or not a population is sustainable. Enery and resource usage determine if a particular lifestyle is sustainable for a given population. Given sufficient energy other resource problems tend to go away (e.g. the amount of various minerals that are in solution within the oceans is mind-boggling but it takes energy to get them out). In the end the lifestyle any particular population can sustain will come down to an energy production/capture and management problem.
> Energy and resource usage determine if a particular lifestyle is sustainable for a given population
And maintaining a particular lifestyle tends to be a strong catalyst for war as a means of solving population problems. The problem is we're now at a point where such a thing could be truly devastating.
While the threat of mutually-assured destruction has kept the specter of nuclear war at bay, I believe you'll see the means of destruction migrate to more fine-grained methods, most notably genetic engineering and nanotechnology, both of which will become increasingly accessible on a scale nuclear technology never has.
> Given sufficient energy other resource problems tend to go away
I agree but all the energy replacements in the foreseeable future will make energy more expensive not cheaper.
Fission-based energy has the same fuel problem fossil fuelds do (the unfulfilled promises of thorium reactors notwithstanding).
Fusion-based energy has huge problems, some of which are fairly fundamental and not likely to be solved anytime soon.
The most obvious problem (containment of plasma) is probably solvable with magnetism.
The bigger problem is neutrons. You currently can't leave a fusion reactor on for very long before it starts destroying its container.
He-3 (Helium-3) is one possibly solution to this but that stuff is incredibly rare and may well present the same fuel problems as any other energy source.
Interestingly there's a supply of it on the Moon due to billions of years of solar wind on an atmosphere-less body.
> In the end the lifestyle any particular population can sustain will come down to an energy production/capture and management problem.
With some fairly nasty corrections that may have undesirable consequences for the rest of us.
Anyway, that's why I say food is the least of our problems. We can already produce enough food for the present population. It's unclear how much longer we can support the lifestyle of that same population.
Energy factors in here too as we're now fairly distant from our food (given how urbanized the developed world generally is) but population redistribution will occur naturally as the energy equation changes.
Actually, food is the only problem when it comes to whether or not a population is sustainable. Enery and resource usage determine if a particular lifestyle is sustainable for a given population.
Food needs aren't static: They vary considerably from person to person and can be changed for a particular individual who sets out to change their lifestyle. Also, a lot of the energy that is currently being expended for transportation could be readily replaced by human energy if walking and biking became more popular -- which is both an energy issue and a lifestyle issue.
I currently live without a car and I have a medical condition that typically causes one to have a very high calorie need. I've worked hard on getting myself healthier and my calorie need has shrunk dramatically. In some ways it is counterintuitive, but living without a car has turned out to be an asset in that regard. Doing a lot of walking is one of the things that has helped me get healthier and shrink my calorie needs. Obesity is epidemic in the US and we do not have a very pedestrian-friendly environment. Most Americans seem unable to imagine living without a car.
So this assumption that energy and some kind of non-food fuel are separate from food and people just doesn't quite compute for me. They aren't totally separate issues. If people walked more and drove less, it would leave more gasoline and other fuel sources for other things and, at least in America, likely substantially lower food needs as well.
Energy is a bigger problem. While we can make energy from renewable sources it is far more expensive (which has ramifications for our entire way of life) and not yet established that we could provide it on the scale necessary to replace our non-renewable sources.
But the biggest problem is resources. Metals, rare earth elements and the like. These are largely irreplaceable in the sense that we can produce so much of them by (typically) digging fairly shallow holes in the ground. We're already going to some fairly inhospitable places to meet our insatiable demand (eg the Arctic in northern Canada and Europe, the Andes).
If we're not careful we may well find our own answer to the Fermi paradox.