All of the carbon we put in the atmosphere was transported (oil, coal, etc) to the location where it was used so this rings false. Presumably the carbon will be pulled from the atmosphere on site and stored on site anyway.

Maybe something like building solar arrays in semi-arid regions and mixing up the resulting solid carbon into the local soil for some ecological engineering or filling up old mining pits.

The carbon gains 2 oxygens when combusted, tripling the weight of the original fuel

Presumably it also loses 2 oxygens when it is turned back into solid carbon.

Well we do move that 40 billion tons to the atmosphere. If we can do that, then in principle we can do the reverse. We just need an economic framework to pay for it.

It's certainly going to be cheaper, in most cases, to avoid emissions in the first place. But there will also be cases, like long-haul jets, where it may be cheaper to remove the CO2 later. Plus the CO2 is already above a safe level, so we'll have to draw it down somehow anyway.

We only move a small portion of the 40 billion tons. Most of the mass of CO2 is oxygen, which was already present in the atmosphere before we combined it with carbon.

Even assuming you can do some kind of reaction in-place, CO2 is over 25% carbon by mass. 10 billion tons is still a massive challenge.

But don't we only need to "first" remove just enough of that 10 billion tons to maintain where we are now, so that we can then remove more to "go back to levels earlier in modern time"?

Yeah, we need to go extremely carbon-negative, not merely carbon-neutral. It's so easy to forget this.

Why?

Why do we need to go carbon-negative? Because the atmosphere already has too much CO2, and reducing net emissions to 0 means that CO2 will stay there. We've emitted that CO2 in the course of (say) 300 years but need to pull it down in (say) < 50 years, hence we need to pull it down much faster than we emitted it.

Not sure if that answered your question or if you meant something else.

Yes, but what I wanted to know is if we kept the current concentrations would temeperature keep rising or would it stay basically the same as it is today.

It would stay the same. And nature would reduce current concentrations back to normal over the next few centuries.

Thanks - that did help me.

Related, for comparison: apparently planting 20B trees/year requires only $80M/year (!) and would pull down a trillion tons of carbon over 50 years (!): https://www.youtube.com/watch?v=QyQvfaW54NU&t=14m53s

But they would decay, unless something is done to sequester enough of the wood, and release much of it back into atmosphere, right?

Cross-laminated timber comes to the rescue. Plus the added benefit of being able to replace concrete, which is a huge bonus for decreasing emissions. And it's already in use.

https://en.wikipedia.org/wiki/Cross-laminated_timber

> unless something is done to sequester enough of the wood

I think that was the idea. He's viewing it as a mass transfer problem. You "harvest" CO2 with trees, then put it back in the ground.

I think the hard part is not hurting ecosystems in the process, but at this point honestly this might still be the best solution we have available.

Unfortunately, the people that plant trees have economic incentives to not put it back in the ground. Timber has considerable economic value, as fuel, or contruction materials or whatever. It's hard to imagine foresters cutting down valuable trees, and then discarding them in some lake.

I imagine it would need to be government funded, not for private enterprise. If the order of magnitude of the costs they mention are to be taken at face value ($80M/year), for the entire world, it would be absolutely trivial for the government to fund, so I don't think expect any commercial enterprise would necessarily be forced to align this with its mission.

> For the entire world, it would be absolutely trivial for the government to fund

Which government? Is that some hypothesised World Government?

The UK Government runs a lot of the forestry in this country. It is run as a commercial timber operation. The Brazilian and Indonesian governments appear to be committed to commercial exploitation of enormous amounts of old-growth rainforest timber. The Polish and Hungarian governments are also committed to logging old-growth.

There's no time left for this kind of dreaming.

> Which government? Is that some hypothesised World Government?

I meant the US government. But you can insert lots of other governments in there, including the UK like you mentioned.

> There's no time left for this kind of dreaming.

Nobody's dreaming. I'm just talking about the feasibility, not claiming anything about the likelihood.

I don't know what kind of construction materials your house is made of, but most wood construction doesn't just vaporize into the atmosphere as CO2 unless it's burnt down, which is considered an undesirable outcome to be prevented.

"then put it back in the ground" - throw it into a lake. Or artificial bogs. When its submerged, the lack of o2 causes the carbon to stay as it is. This is basically how coal comes into existence.

The whole lumber shortage thing makes me think that people are willing to sequester wood in their homes. (I know, I know, it was sawmill capacity or something. But still...)

Most trees are planted in order to be harvested as timber. Most of that timber turns back into CO2 in 100 years or so. Tree-planting is not a long-term solution to excess atmospheric carbon. Combined with carbon-trading, tree-planting is a rather obvious channel for greenwashing.

> Most of that timber turns back into CO2 in 100 years or so. Tree-planting is not a long-term solution to excess atmospheric carbon.

Do you have links to more reading on that? This is the first time I've heard of this particular reason why it might not work.

No I don't. But if wood lasted more than a couple of hundred years on average, then we would be neck-deep in old lumber. We're constantly cutting down trees, and yet the amount of wood in the lived environment isn't increasing noticeably.

Conclusion: all that old wood is either buried, or it's busy turning into CO2.

So I'm not impressed by claims of "carbon offsetting". On the contrary, I take such claims as evidence that the organisation in question is part of the problem.

Incidentally, how are you supposed to recycle chipboard? Like, for example a chipboard kitchen counter? For several decades, I had in my home a pair of oak side tables, that were made by my grandfather from the remains of a large oak dining table. You can't do that nowadays with chipboard.

I can't say I follow your logic at all unfortunately.

But regardless, I also don't get where you see a discussion of "carbon offsetting". This isn't about "offsetting" emissions or impressing you, this is about repaying "debt" that's already incurred. Pulling down old carbon is something we have to do regardless of what we do with our current emissions, even if we drive them to 0, because the current carbon in the atmosphere is already too much. Whether we do it with trees or machines or something else, it needs to happen.

Wooden things rarely last more than 50 years and end up being thrown in fire, or catching fire as a result of natural events. Additionally, decaying wood releases CO2.

It depends on how you use that wood. In old cities around the world, there are plentiful examples of wooden structures that have been around for up to 1000 years or more.

Does our current world really look like we're building thousand year long buildings ?

Well I believe we should be moving in that direction if we want to have any chance of sustaining society. Just like we need to kill fast fashion, we should kill "fast construction" too.

But only about 16% of that mass of CO2 was ever "transported" in the first place: the carbon atom. The O2 part appears for free because it comes out of the air the fuel is burned in. And that oxygen wouldn't be transported with carbon capture either, it would just be vented into the atmosphere again.

I mean think about it, we can't be emitting more waste than we are transporting, because that waste comes from fuel, and the fuel itself is part of what we're transporting.

And then there's the fossil fuel dependency. We still need more than will be produced, even ignoring CO2 levels.