Most our energy comes from fossil fuels. Even fertiliser for our food. So we can't just replace it all with solar power.

One key questions for rulers and governments from antiquity is how to allow the population to gather energy to survive. It could be farming, or building oil wells and then hand out the profits or build a service economy around the oil.

I couldn't figure out how to maintain a modern population without oil (more people same amount of land) until I saw this on HN the other day https://medium.com/invironment/an-army-of-ocean-farmers-on-t...

Zero input food. Can be used to generate ethanol. All you need is open ocean.

Food for thought.

> Most our energy comes from fossil fuels. Even fertiliser for our food. So we can't just replace it all with solar power.

But we can with nuclear plants, and I'm thinking garden variety fission plants, not the always-30-years-from-now fusion ones. There are various areas where we use fossil fuels only because its more convenient - e.g. ground transportation. We can go electric with most of it. Fertilizers - I'm not sure if petroleum is a necessary chemical component or just energy delivery vector for the production process. Plastics are I think the only area where we can't easily sidestep fossil fuels. But with enough electricity we can still synthesize the compounds we need for those processes.

I have thought about this problem and came to the same conclusion - we need to move to nuclear. But then if most of our energy needs are from nuclear, now we're going to be back in the same situation in 50 years running out of uranium.

Or we could sit in top of our coal power plants slurping oil, wait for the magical thorium reactor and/or solar power to become another 10 times more economical.

Maybe not in 50 years, because it seems that we have a lot of fissile material available[0] that should last us for a long time - long enough to expand past this planet if we continue the growth curve, or at least to advance and deploy renewable solutions without a hurry. But yeah, with continued growth we would hit an energy ceiling in the future too. That ain't bad if reasonably managed - we could fix all the damage done to this planet and expand to the Solar System. But then again, humanity isn't exactly known for reasonable management.

[0] - http://www.withouthotair.com/c24/page_162.shtml

http://www.withouthotair.com/c24/page_162.shtml:

>> "A once-through one-gigawatt nuclear power station uses 162 tons per year of uranium"

>> "World total (conventional reserves in the ground) 4.7[million tons]"

https://en.wikipedia.org/wiki/World_energy_consumption

>> "The IEA estimates that, in 2013, total world energy consumption was 13,541 Mtoe , or 5.67 × 1020 joules, equal to an average power consumption of 18.0 terawatts.[3]"

One gigawatt nuclear plant uses 162 tons per year.

The world uses 18000 gigawatts per year. (40% oil, 10% coal, 15% natural gas, 35% other).

If all the fossil fuel-based energy were replaced with nuclear power, the nuclear power plants need to provide 18000 gigawatts times 65% = 11700 gigawatts.

11700 gigawatts times 162 tons of uranium is 1.9 million tons of uranium, per year.

The world's conventional reserves of 4.7 million tons will last for three years.

The 22 million tons in Phosphate deposits will last for another 10 years. (if and when methods to mine them economically are discovered)

Perhaps the seawater uranium will come in time, but as yet it is not an economical method of uranium extraction. The cost needs to be reduced by 5 to 10 times.

> Most our energy comes from fossil fuels. Even fertiliser for our food. So we can't just replace it all with solar power.

That doesn't follow at all. Why not?

There's plenty of sunlight in the areas with most of the people, and the areas with most of the farmland. We have storage solutions--they're still a little expensive, but they're certainly getting close.

If our current energy came from hydroelectric or geothermal could we replace it with solar? Your statement seems like a complete non sequitur.

This statement may be wrong but for different reasons - it boils down to just how much electricity vs. petroleum we need to use to make fertilizer. I don't know much about fertilizer manufacturing, but from a quick look at Wikipedia I think that for nitrogen ones we could conceivably replace natural gas with some other hydrogen source and run the whole Haber-Bosch stack off electricity.

Why not run the world on nuclear power? With breeder reactors, there is enough uranium for more than million years of current world electricity consumption. Nuclear energy is cheap, and modern reactor designs are safe.

It's never cheap. It's plagued by construction cost overruns. We're having this problem with Hinkley Point C at the moment: http://www.theguardian.com/business/2016/mar/11/edf-chief-ex...

Even given the cost overruns, insurance, nuclear pools, etc it is quite cheap. The only problem with nuclear power is that it is highly centralized and requires significant upfront capital expenditures. And political consequences of radiophobia are so high that investing in nuclear power is limited.

I think that solar and nuclear are the only sustainable power generation methods these days. The rest are either bad for the environment, or ineffective.

Radiophobe here.

I can't accept the morality of handing stewardship of spent nuclear fuel to my children and their children for a thousand generations. Would you still want to be caring for a monster left to us by the people who wrote on cave walls?

As far as a DGR, I'll believe it when a nation other than Finland has shovels in the ground to actually build one.

Nuclear fuel waste is much less dangerouns than many other substances created in industrial chemical processes, and occur in much smaller amounts. Managing that is a non-problem compared to other hazardous waste. That people are afraid of radioactive waste and aren't of what their friendly neighbourhood chemical plant produces is pure FUD.

Not exactly, unfortunately. (I am as pro-nuclear as one could be). However, all chemical waste can be neutralized and reprocessed (though this might be expensive to do so). Some nuclear waste can't be reprocessed and has to be stored safely for hundreds of years. This scares some people.

However, it's not _that_ dangerous. Even if containment is breached, it generally stays in the same place and can be collected and put back (happened a lot of times).

> Even if containment is breached, it generally stays in the same place and can be collected and put back (happened a lot of times).

Asse II springs to my mind: https://en.wikipedia.org/wiki/Asse_II_mine An old salt mine used to store low/medium radioactive waste that's under threat of collapse due to ground water. There are plans for the retrieval, but success is far from guaranteed.

This might be a dumb question, but is there any reason other than costs that we couldn't eventually just blast unrecycleable nuclear waste off into the sun/space? There must be an inflection point where the cost of storing the hazardous material safely on earth is more expensive after a period of time than just sending it out of orbit on a space elevator/ICBM.

Sending things to outer space is crazily expensive in terms of fuel; the same holds if you aim for the Sun - the common idea that it's easy is very wrong. The Earth is moving around the Sun at 30km/sec, you need to burn off most of that velocity to actually hit it. For leaving the Solar System, the Internet provides the value of around 40km/sec. You can get most of those speeds by clever use of slingshot maneuvers though, and this is the way we usually do missions to outer planets.

Also, honestly, I don't see the point. The amount of nuclear waste we produce is minuscule compared to other equally or more dangerous chemical substances. Besides wasting perfectly good rocket fuel, destroying it this way would rob us of opportunity to reuse it in the future - hell, we already know how to reprocess some of the spent nuclear fuel for next-gen fission reactors!

1) Breeder reactors are reducing the amount of spent fuel to store about 100x. Existing nuclear waste can also be reprocessed.

https://en.wikipedia.org/wiki/Breeder_reactor#Waste_reductio...

2) What monster could be left by stone-age people to us that modern technology couldn't handle?

Modern spent fuel processing methods are great and quite safe (vitrification / underground disposal). I can't imagine a newsworthy worst case scenario with vitrified containers.

1) Sodium-based breeder reactors are terrifying, and considered by most to be a dangerous failed experiment: https://en.wikipedia.org/wiki/Breeder_reactor#Breeder_reacto...

2) As long as we assume that society continues on its current trajectory forever, then yes, there's nothing to worry about. But if it's true that we're in the twilight years of US dominance or relevance as a world power, then we could be in for a significant period of upcoming political/economic turmoil.

So here's another way to look at it: How would the monks and agrarian fiefdoms of the middle ages been at handling a monster leftover by the Romans?

"Caring for" meaning simply not entering the tomb labeled "This is not a place of honor"?

Thousands of years is a really long time, especially when you look at how awful people are at learning the lessons of just a generation or two ago.

Yes, I agree. I might have not worded my comment clearly enough. What I meant is: I don't see the world being full of nuclear powerplants right now, so we don't have a sustainable energy surplus to stupidly waste.

EDIT: Fixed wording in the original comment; I hope it's clearer now.

No, it's not, that's a bit too simple.

In reality, time is the metric the matters, human time. All that stuff you talk about costs human time to build. That's why it's not being built - it's cheaper to do something else.

Once you have a robotic army capable of mining resources and building everything you want, including rebuilding itself, you can just have them throw up a bunch of solar panels and have enough energy for desalination.

I disagree. Human time is not a problem. Yes, in a moral world it would be the most important metric. But nowadays, labour is cheap and abunant. That's why we don't have robotic armies doing stuff all around us - it's cheaper to make people work. We're energy-bound as a civilization now (or, one could say, still).