[SEJeff]

Methane can be created via carbon capture entirely. It is in the SpaceX TODO list to create a factory to literally create metholox (methane + liquid oxygen is what they use as fuel for the new Starship / Superheavy rockets they want to use to go to mars) via carbon capture. Elon has already discussed this before. The end goal that the rocket launch is carbon neutral when you are using carbon already captured from the atmosphere.

Here is a good overview of the plan: https://cleantechnica.com/2019/10/30/no-you-dont-have-to-wor...

[hoseja]

The goal is not being carbon-neutral. The goal is Mars ISRU.

[SEJeff]

Elon has explicitly stated in interviews that one of the benefits of the design is that here on earth, it means they can be carbon neutral. I'm just relaying what he's publicly stated already. Yes, Mars ISRU is a HUGE benefit of this design, but it also means they can make their own fuel here on Earth with nothing more than some big machinery and solar panels.

I believe his exact quote was:

""" Sometimes I get criticism for, ‘why are you using combustion in rockets and you have electric cars’. There isn’t some way to make an electric rocket. I wish there was. But in the long-term, you can use solar power to extract CO2 from the atmosphere, combine it with water, and produce fuel and oxygen for the rocket. """

[8bitsrule]

"There isn’t some way to make an electric rocket. I wish there was."

That Musk is no Tom Swift. Tom even had an electric rifle, not just a flamethrower.

which he used to great advantage in colonizing Africa

[WalterBright]

The whole "carbon neutral" think is a crock. Coal is, after all, just dead trees, so coal plants run on "biofuel" and are "carbon neutral".

[m-i-l]

> The whole "carbon neutral" think is a crock. Coal is, after all, just dead trees, so coal plants run on "biofuel" and are "carbon neutral".

The difference is in the timeframes for capture and replacement - with coal it is millions of years, and with wood it is years. That means burning coal releases carbon which was trapped millions of years ago, and it would take millions of years to trap equivalent amounts of carbon with the formation of new replacement coal deposits. Burning wood on the other hand releases carbon that has been trapped within our lifetime, and it is easy to replace with new trees grown in our lifetime. Bear in mind that if we reverse millions of years of carbon capture we would revert the atmosphere to what it was like millions of years ago, and time travellers visiting that era are likely to need breathing equipment.

[ppf]

True, but what is a sustainable level of tree harvesting to feed the world's energy needs?

[eloff]

That's not possible, our energy needs are too great for that now. But nobody would seriously suggest wood (or other biofuels) be our principal energy source anyway.

[ppf]

That's my point. Any scheme involving burning wood to create aviation fuel is an indicator that the wrong side of the energy usage balance is being addressed.

[ben_w]

Technically correct, but about as unhelpful as saying “solar isn’t renewable because the sun will eventually go out”.

Our biology and our biosphere are not adapted to the atmospheric CO2 levels we would have if we burned all the fossil fuels.

[WalterBright]

My point is calling something "carbon neutral" if it is burning wood is equally unhelpful. Nothing is gained by burning a tree you just chopped down instead of burning a tree buried for a million years - the same amount of CO2 is released.

[mkl]

But the tree you just chopped down got its carbon from the atmosphere just a few years ago. That's what makes it carbon neutral. The coal (/gas/oil/etc.) got its carbon from the atmosphere in the far distant past, so from our point of view it's new additional carbon that wasn't in the system before. It can only be considered carbon neutral over a time span of millions of years, which is pretty meaningless.

[WalterBright]

> That's what makes it carbon neutral.

Nope. You're emitting exactly the same CO2.

Want to be green? Burn less. Changing your point of view won't lessen CO2 emissions. Burning less carbon will.

[ben_w]

The CO2 emissions are not themselves the point, the CO2 concentrations are. The concentration is neutral in time scales we care about from wood/alge/bioethanol/etc., but goes up from fossil fuels.

It’s also fine to burn fossil fuels if you can make long-term carbon sinks from other processes, hence people caring about making carbon-rich rocks or whether dead plankton floats our sinks.

It’s a question of being responsible for the consequences of actions, not outright banning those actions before the alternatives have been deployed at scale.

[DagAgren]

"Unhelpful"? We have a specific problem we are trying to solve. That problem is: Too much CO2, right now. The term is obviously useful in solving that problem.

Nobody is worrying about CO2 on geological timescales. It is simply not relevant to any discussion anyone is having, or any problem anyone is trying to solve.

This isn't complicated? How are you managing to miss the point with such vigour?

[WalterBright]

> How are you managing to miss the point with such vigour?

I could ask the same of you - how are you helping matters at all by chopping down a tree and burning it over digging up a tree and burning it? You're emitting the same amount of CO2.

Want to reduce global warming?

1. plant a tree

2. burn less

If you're wondering what to do with the tree after it grows, you can:

1. use it for lumber

2. bury it

[DagAgren]

One does not make the situation worse. The other makes it worse. That's pretty simple.

Neither makes the situation BETTER. But one makes it WORSE.

[Tagbert]

The carbon neutral part is when you plant another tree in place of the tree you just cut down. The new tree then starts taking up the equivalent carbon from the tree you cut down and burned. That is what makes tree farms somewhat carbon neutral. You can’t do that with coal.

[dboreham]

There's an implicit time window on the sum. Burning fossil fuels is evaporating all the carbon captured in the past billion years, over a few hundred years.