[not_jd_salinger]

> the fact that humans beings are doing better than they've ever done in our history by almost every imaginable metric.

That's because we have had ready access to insanely abundant high-energy density source of energy.

The non-fossil fuel supported carrying capacity of the planet for humans is estimated to be somewhere around 1 billion people. When the fuel runs out (if we don't cook ourselves first), that will collapse.

It is nothing intrinsic about humans that have lead to our recent success, just access to lots of nearly free energy.

edit: why the downvotes? Is there even anything controversial in these statements? HN's fear of bad news is getting out of hand.

[myrmidon]

What is your source for the 1 billion estimate? Because that seems completely, non-credibly *low* to me.

I also strongly believe that we could cover all our energy needs with renewable sources within a few decades if we really wanted to (even assuming no significant advances in tech), and this seems mostly non-disputed to me (because that is literally what nation-states are currently planning/doing).

> Is there even anything controversial in these statements?

Yes. Your statements seem not credible to me and you cite no sources.

[not_jd_salinger]

1 billion is a rough estimate based populations prior to the massive boom in the industrial revolution that saw massive changes in the way agriculture is done. It could easily be 2 billion or so, but definitely not 7.8 billion. You can see the population history here[0.]

To see the powerful impact of fossil fuels on carrying capacity you'll notice there's an important inflection point around 1920-1930. This is because of the advent of the Haber process[1] which allows us to use fossil fuels to create nitrogen based fertilizers.

Lest you doubt the impact of the Haber process just look at trends in corn yield per acre since then [2]. It's truly remarkable. Additional gains there are from other industrialized, fossil fuel driven agricultural process.

The Haber process requires hydrocarbons. In the wikipedia article you can see that it consumes 3-5% of the worlds natural gas production and 1-2% of the global energy supply.

We have completely disrupted the natural nitrogen cycle [4] and so would be unable to produce anywhere near as much food without fossil fuels. Because we have disrupted this cycle it's not even obvious that we could go back to a world of pre-fossil fuel agriculture.

So those are just some bit of information about my claims but let's take a look at yours:

> we could cover all our energy needs with renewable sources within a few decades if we really wanted to... this seems mostly non-disputed to me

This is wildly disputed, and I don't know anyone who credibly believes this without invoking "magic" future technology.

For starters we haven't replaced fossil fuels with "renewables" at all so far. We've just used them to supplement our energy needs. You can see here [4] that global fossil fuel consumption has continued to rise.

Then it is important to separate electricity from the more general subject of energy. Currently only 20% of global energy usage is electricity generation [5]. So even if you replaced the entire grid with renewables over night you would still be missing the vast majority of energy demands.

We currently have no viable pathway for renewable energy in transportation. Alice Friedman has more notes on this than I could ever fit in a comment [6]. Transportation inherently requires high energy density fuels, and outside of passenger vehicles, battery technology does not have the density required for industrial shipping.

It worth looking at our national energy flows to get a good sense of just how little of the energy we use comes from renewables [7].

But even if we look just at the electrical grid, in the US, we have some very obvious problems with "all" our needs. As you probably know, wind and solar are intermittent power sources that requires fossil fuel powered "peaker" plants to provide energy in down times.

This had two problems. One you need energy storage technology that we do not currently have (you cannot use grid scale lithium batters, pumped hydro has geological constraints, molten salts only work with concentrated solar, compressed air requires decommissioned oil field, etc).

The other problem is that even if you had perfect storage you need to now more than double the total energy production so you can fill those batteries.

The should be enough sources for you to get started, but I have feeling I'll still get down votes and "hand wavy" explanations of how it will all work out.

0. https://en.wikipedia.org/wiki/World_population#/media/File:W...

1. https://en.wikipedia.org/wiki/Haber_process

2. https://www.agry.purdue.edu/ext/corn/news/timeless/YieldTren...

3. https://en.wikipedia.org/wiki/Human_impact_on_the_nitrogen_c...

4. https://ourworldindata.org/grapher/global-energy-substitutio...

5. https://www.iea.org/reports/world-energy-outlook-2019/electr...

6. https://www.resilience.org/resilience-author/alice-friedeman...

7. https://flowcharts.llnl.gov/content/assets/images/charts/Ene...

[myrmidon]

Thanks for explaining how you arrived at your numbers.

> I have feeling I'll still get down votes and "hand wavy" explanations

Let me turn this around: you are getting downvotes (not from me) because your 1 billion population carrying estimate in a post-fossil age is implausible and borderline disingenuous:

1) It assumes that pre-industrial agricultural output is the maximum that our planet can sustain. Which is completely off for a multitude of reasons:

- Genetic improvements to cultivars still fully apply

- Pesticides won't cease to exist

- Automation in harvesting/monitoring also won't go away

2) There is no reason to assume that we're anywhere close to peak sustainable agricultural output, neither in pre-industrial times NOR now.

3) Furthermore, it implies that land utilization, cultivar choice and consumer behavior in general would stay similar/comparable regardless of cataclysmic change in supply/demand (pricing). Which is obviously wrong: If avocado price went up to 50$/kg then people would just put potatoes on their toast instead, and total agricultural output (in calories) would "inexplicably" increase.

Regarding power:

Renewables (solar/wind) are a perfectly fine source of primary energy. Storage/grid stability does not depend on "technology we do not currently have"--Batteries and inverters are perfectly usable, mature technologies--but right now slapping down natural gas plants is simply cheaper. This is exclusively a matter of price/ROI, and installation could be jumpstarted immediately if there was the political will to pay for it (and thats not blaming politicians exclusively to be clear--average citizen is simply unwilling to pay 1$/kWh right now for residential electricity).

> Renewable energy in transportation

Friedman selfdescribes as "energy sceptic" which is already...unfavorable... to me and after stumbling over "running out of fossils is gonna solve climate change better than anything else" (transcribed), I gave up on the author completely;

Viable pathways are:

- Batteries

- Biofuel

- Fuel cells

- Hydrogen in combustion engines

We literally built all of those already, but same story here: It's less cost efficient than burning diesel right now, so why would anyone do it.

[not_jd_salinger]

> It assumes that pre-industrial agricultural output is the maximum that our planet can sustain. Which is completely off for a multitude of reasons

I agree it's off because we've done significant damage to the biosphere since industrialization. As I've pointed out we have disrupted the natural nitrogen cycle.

If we where to immediately rewind our population back to 1850 and try to life that lifestyle we would have a much harder time since we have depleted natural resources. We cannot go back because we the earth would not support us the way it once did.

> There is no reason to assume that we're anywhere close to peak sustainable agricultural output, neither in pre-industrial times NOR now.

Our entire current agricultural system relies on fossil fuels, so I agree, where nowhere near close... we're way past.

> Viable pathways are

- batteries: not for commercial transport, the energy density is still way too low. Your battery becomes your cargo. Modern global trade is impossible in a battery based economy. Nobody that is serious on renewables will disagree with this, they will claim that new battery technology is going to solve this.

- Biofuel: require more energy to make they they provide [0]. So again, not only do you need to double the grid to handle intermittent power, you now need to expand it by the total biofuel energy required times 1/efficiency, so we're looking at at least tripling our current power output and trying to do it with only renewables. Please tell me how much silicon and lithium it would take to build a grid that large in that sort of a time span and you'll find it dwarf's annual production.

- Fuel cells: same problem again, currently fuel cells are made with coal or natural gas today 95% of fuel cells are made with natural gas [1]. If you want to switch to electrolysis you come up with the same problem of having to double our current grid power.

- Hydrogen in combustion engines: I'm not sure how this is different from hydrogen fuel cells, but the hydrogen production problem is the same.

Please if you want sources, provide some of your own. Come up with some back of the envelope estimates on the total grid capacity needed to cover 100% of our energy needs. Then do some research on the energy costs to produce solar cells at that scale (or wind farms, hydro is already near full capacity at least in the US).

I know you yourself don't really believe what you are saying. It's based on no research, you have provided no meaningful sources, and even the most die-hard solar/renewable proponents realize that grid scale storage is still an unsolved problems. What you have given are "hand wavy" explanations without sources, exactly as I expected.

0. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7320919/

1. https://www.energy.gov/eere/fuelcells/hydrogen-fuel-basics