I do agree wholeheartedly, but the problem with trees is that they die and then they rot releasing all that carbon back into the atmosphere. It's a good start though! It be awesome if we had some sort of technology that sequestered carbon (where it be in the form of CO2 or wood chips, and sorted that carbon in a solid form effectively indefinitely. for trees to be a permanent solution, we would have to convert 50% of the land we use agriculturally to woodlands and and then better utilize the remaining land for food production. /shrug

This is a problem with 'organic' sequestration. However, trees are relatively long lived and take a long time to fully decay. Suitably harvested and treated wood also lasts a long time. Young growing trees sequester the most carbon, so you could have a cycle of logging older trees and replanting shrubs to maximise the sequestration. Some types of bamboo grow incredibly fast, as much as 90cm a day.

I did some back of the envelope calculations. It would take something like 240 billion extra trees to return us to pre-industrial carbon dioxide levels. This sounds like a lot, but it certainly isn't physically impossible. The Amazon has 400 billion trees. Finding suitable land mass for this purpose is an issue. But trees are remarkable, they grow in many inhospitable places. Mangroves for example survive in very difficult conditions with salt water and changing tides. So there is not necessarily an overlap with arable land. There are always more ambitious things you can try, like GMO trees that can grow in the desert, or giant floating forests in the Pacific

Also, if we could stop deforesting the Amazon currently, that would be a good start

The co2 released by a dead tree is captured again by the next tree. So don't look at single trees but at whole forests.

Which means less atmospheric carbon that we actually want to scrub gets captured by that 'next tree'...

Charcoal?

The main question is whether there's a carbon sequestration process which can be industrialized so that it's more effective than planting trees.

Not sure we want to start competing with trees -- what if we get better than them at it? Do trees start dying for lack of CO2?

If we could process enough CO2 to reverse current inputs(i.e. the equivalent of hundreds of billions of tree growth) we could possibly think about scaling up the process to remove all the CO2 from our atmosphere as fast as we can. But we won't run out of CO2 unless we take all the ethanol we're producing with the CO2 and store it, instead of generating energy from it via combustion.

It's not like we couldn't stop if the CO2 levels dropped too far.

Just like we are able to stop now, as the CO2 levels are life-threateningly high, right?

Plants capture about 1% of the incoming sunlight energy into chemical energy. We might be able to come up with a process that is more efficient.

But would the process scale? If it requires substantial amounts of rare earth minerals or very energy intensive manufacturing it will still be unworkable.