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Comment by mrob | Hacker News Reader

Heat pollution is a very minor concern. From "Sustainable Energy – without the hot air" by David MacKay, pages 170 to 171:

"let’s assume that in 100 years or so, the world population is 10 billion, and everyone is living at a European standard of living, using 125 kWh per day derived from fossil sources, from nuclear power, or from mined geothermal power. The area of the earth per person would be 51 000 m^2. Dividing the power per person by the area per person, we find that the extra power contributed by human energy use would be 0.1 W/m^2. That’s one fortieth of the 4 W/m^2 that we’re currently fretting about, and a little smaller than the 0.25 W/m^2 effect of solar variations. So yes, under these assumptions, human power production would /just/ show up as a contributor to global climate change."

http://www.withouthotair.com/c24/page_170.shtml

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That's assuming that we use the same order of magnitude of energy.

If the promise of a technology is that we can use several orders of magnitude more energy per person, then that .1W/m2 could become 10W/m2.

If we don't increase energy usage, sure, no big deal, but the entire point of pursuing fusion is to enable fantastically more energy usage, at least as I see it.

So we also need a second revolutionary technology, direct conversion of energy rather than thermal energy conversion.

Fusion will never be a cost winner if it's using thermal energy conversion, anyway. Solar and wind will soon undercut the steam turbine lifetime costs, so even if the fusion part were free, there's no way for heat engines to compete on cost.

> the entire point of pursuing fusion is to enable fantastically more energy usage

No, it's to enable enough energy usage for, as MacKay says, a first world standard of living for the entire world's population, instead of just a small fraction of it. That's more than today, but not fantastically more.

Also, as technology advances, the energy usage required for a first world standard of living goes down. Our entire house now has LED bulbs; that cuts our energy usage for lighting to about 10% of what used to be the standard (incandescent bulbs), or about a third of the previous "low energy" standard (fluorescent bulbs--which also have hazmat issues since they contain mercury). Computers today use only a small fraction of the energy of older computers while still delivering more computing power. HVAC systems and refrigerators are more and more efficient. Cars are more efficient--I have a small SUV with a four cylinder engine (up until a few years ago I would never have even considered a four cylinder engine for an SUV, but this one has good enough performance) that gets better gas mileage than the 4-door sedan with a V6 engine that I had before it. The list goes on.

> If the promise of a technology is that we can use several orders of magnitude more energy per person, then that .1W/m2 could become 10W/m2.

Depending on what type of energy you exactly have in mind.

It is totally possible to increase consumption of iee. electric energy and reduce overall energy needs. We burn most of the fuels and use them very inefficiently:

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

In short: you need to burn coal with 3x as much energy to generate 1x of electricity. So when you switch from coal to nuclear (or renewable) and increase 2x your energy usage you still come up ahead in total primary energy consumption.

This comparison isn't valid for nuclear; nuclear power plants use steam turbines to convert heat to electricity, just like coal plants do, and the thermal efficiency (fraction of energy from burning the fuel that actually becomes electrical energy) is about the same.

OK, I double checked and you're right. Nuclear is counted properly difference is only for renewables:

https://energypost.eu/iea-underreports-contribution-solar-wi...

I have the feeling when we do hit the first milestone on the Kardashev scale that we'll have a lot more options available to mitigate terrestrial concerns, so let's just concentrate on getting there without killing the planet first

I've never understood why people get excited about the Kardashev scale. It's a proposal for classifying civilizations which has no place for the one and only civilization we actually know of. Doesn't that make it kind of silly?

It works great for conversation like this. It lets a person summarise 1 wiki page worth of assumptions and definitions into a single line and quickly establishes an order-of-magnitude scale to frame the discussion.

Fiction, science fiction and storytelling generally are ideal for that sort of usage. They let people pre-consider a lot of the arguments and assumptions of the people they are talking to.

I agree that I would like more energy. If it was limitless you could do all sorts of things that are not really worth it today. Imagine being able to have a hot water tank at the back of your property just because it is nice to wash your hands with warm water. Or to keep your bathroom floor always heated. May as well get a hot tub can finally afford to power that year around. I could go on forever if I had cheap energy. So as you say energy consumption may go up if made possible.

> Heat pollution is a very minor concern.

WOHA was a cursory and self acknowledged "back of the envelope" style reference, it is also now outdated.

Heat pollution is often not a minor concern locally, see introductions such as "Thermal pollution: an overview"[1]. Even globally heat pollution may have a significant contribution to climate, see studies such as "Global anthropogenic heat emissions from energy consumption" [2]

>Although the mean Antropogenic Heat Flux is small compared to the forcing of GHGs, it may exert quite distinctive effects on the climate and the environment because of the surface-based emissions and uneven geographical distribution.[2]

[1] https://www.sciencedirect.com/topics/earth-and-planetary-sci...

[2] https://link.springer.com/article/10.1007/s10584-017-2092-z

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