Biofuel is carbon-neutral because the carbon comes from the atmosphere. It's fine to burn it because its emissions have already been bought and paid for in its creaion. The problem with carbon is digging it up, in an open cycle.

Renewable is a more strict term than carbon-neutral, it's true, but all "renewables" are by definition closed-loop and hence carbon-neutral.

This is a common but incorrect assumption. Biofuels are very far from carbon neutral. Renewable is in no way restricted to the desirable.

As an extreme case in point, wood in particular is a horrifying energy source due to health detriment from particulates.

Have a look at some data:

https://partofthething.com/thoughts/wp-content/uploads/ipcc-...

Source: Schlomer S., et.al., 2014: Annex III: Technology-specific cost and performance parameters. In: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the 5th Assessment Report of the IPCC

https://www.ipcc.ch/site/assets/uploads/2018/02/ipcc_wg3_ar5...

Setting aside other issues with it like particulate emission, how can it be anything other than carbon neutral? Where could the surplus carbon possibly come from?

When biofuels are valuable, people clear forests to make biofuel. The carbon payback period can be up to 1000 years. It's called indirect land use change [1,2]

[1] https://en.wikipedia.org/wiki/ILUC

[2] https://en.wikipedia.org/wiki/Biofuel#Greenhouse_gas_emissio...

Okay, but the problem we're trying to solve is the carbon being in the atmosphere, so even biofuel is objectively far worse than, say, solar.

Making the biofuel takes exactly as much carbon out of the atmosphere as it releases when burned, so no it is not far worse from a global warming perspective.

While I agree that technically, fusion is not renewable, I feel like it might as well be? Working fusion reactors make it economical to siphon hydrogen fuel from Jupiter and such. Did you mean fission?

Well, technically, nothing's really renewable. Limited but massive nuclear fusion in the sun is indirectly powering solar PV and wind and hydro for 4-10 billion more years. Limited nuclear alpha decay of Uranium inside Earth powers geothermal. The limited Earth-Moon gravitational system powers tidal.

So I think it's fair to actually consider nuclear fusion and nuclear fission in breeder reactors both to be renewable. B. Cohen said the same about breeder fission reactors in the 1980s [1].

Uranium in seawater can be extracted at 10x world energy scale for billions of years. It replenishes continuously through crustal erosion and plate tectonics. Sounds pretty renewable.

But according to policies we're writing today, the term renewable does not include fusion or fission in breeders. I consider this problematic. Thus I think we all should prefer either "sustainable energy" or "low-carbon energy".

[1] http://large.stanford.edu/publications/coal/references/docs/...

I prefer “sustainable”, as in “this technology can be used as some scale for X years without causing major problems”.

High-burnup nuclear power, under reasonable assumptions, is sustainable for hundreds of thousands of years. Fusion is presumably sustainable as long as the Earth exists, as are solar and wind. Coal is not sustainable at all.

Right on. Breeder fission reactors can power civilization for at least tens of millions of years, probably billions, thanks to seawater uranium extraction and renewal through plate tectonics.