Is genetically modified trees to capture CO2 possible?

Tree farms are already a thing, so the idea is not crazy. Likewise, woodland owners tend to manage their forests for sustainable growth, clearing out a selection of trees every few years, making sure there is room for new growth, etc.

So you are on the right track, but may want to do some research get a good sense of what the status quo is, and then seek ways to improve. (And there are definitely ways it can be improved - not everyone is sustainable, not all woodland owners harvest at all, and even the folks who are sustainably harvesting wood could increase production with coppicing or other techniques.)

This is happening. It is better to do it in rice which is widely consumed, staple in most asian countries.

"C4 rice research, currently in its early phases, hopes to develop a new type of rice with improved photosynthesis capacity, known as C4. There are classes of plants known as “C3” and “C4” – referring to how they convert light energy into sugar or photosynthesize. Rice has a C3 photosynthetic pathway. C3 photosynthesis is inefficient at converting inputs to grain, as opposed to the C4 pathway, in which resources are processed more efficiently and converted into higher grain production." [1]

In C3 plants, the carbon dioxide fixation takes place only at one place. In C4 plants, the carbon dioxide fixation takes places twice (one in mesophyll cells, second in bundle sheath cells). C3 plants possess only one CO2 acceptor. C4 plants possess two CO2 acceptors (primary acceptor and secondary acceptor).[2]

[1] https://www.irri.org/news-and-events/news/rice-future-gets-f...

[2] https://www.easybiologyclass.com/similarities-and-difference...).

> Is this idea crazy?

I don't think it's crazy at all. In fact, I had a very similar idea a while back. Genetically engineer plants of some sort to grow faster and absorb more co2? Sure, why not.

> What I am missing?

Good question. I'm a complete n00b when it comes to synthetic biologic / genetic engineering / etc. I know just enough to be dangerous, so to speak.

I did have a conversation about this with a friend who is more knowledgeable about syn-bio / genetics than I am (although not really an "expert" as far as I know) and he was somewhat dismissive of the idea, although I'm not sure I fully understood his reason why. He seemed to be appealing to an idea that "trees have been evolving for billions of years, how likely is it that we'd be able to optimize them in any way?" My counter argument was that trees didn't evolve for any specific agenda like "maximize co2 absorption" (other than "survive") and there's no reason to think that we couldn't engineer them to optimize for something like "maximize co2 absorption". I don't remember exactly what his counter to that was, but I think we ended up not really agreeing about the whole thing. That said, he is definitely more knowledgeable than I am in this overall area, so take that for what it's worth.

Probably be better to grow Wolffia (or duckweed) in vats. Under optimal conditions they can double in size daily, and they are human and livestock edible and can be composted to convert into fertilizer or they could be sterilized and used to feed fish or serve as a food source for lake or ocean farming.

Further, they seem to grow best in slightly acidic highly carbonized water, so you could extract CO2 from the air (by refrigerating the air into a liquid) and dump it into the Wolffia vats for them to convert into plant material.

Worst case, you could burn the Wolffia for nearly direct conversion of CO2 into raw carbon to be buried in old abandoned mines and such.

The problem is that currently growing Wolffia is difficult, and scaling that up to meet the needs of the near future would be an inordinate task, but if someone is up to it then godspeed.

You might find this company interesting: https://www.livingcarbon.com/

There's a great podcast with the founders that goes into some detail about the company: https://www.myclimatejourney.co/ctss-episodes/living-carbon

If you're not familiar with it, the entire my climate journey podcast is great listening and has a ton of interesting companies on it.

They tried making lignin free trees but they get shredded by bugs.

You can cut the branches off willows and have new branches come off the roots quickly, this is called ‘coppicing’ and is used in bioenergy. Beavers do it too.

Bamboo already grows pretty quick, though from what I understand it has some disadvantages in how it tends to be cloned and has mass flowering/die-off cycles.

Figuring out how to make Bamboo grow in more places, and grow faster from seed might be a great way to do this.