Carbon from the earth itself. It just has that much and won't be sequestered forever.
Maybe, maybe not... I haven't heard of anyone actually suggesting eternal sequestering, but I have heard of efforts to match carbon-releasing processes to sequestering processes, so the active amount is controllable.
Are we speeding it up? Of course. But in that process we have developed a remarkable and literate scientific civilization.
...Which will mean approximately nothing without a sustainable ecology. When our society collapses, so does our knowledge.
Will New Orleans end up underwater? Probably. So will many places. We can adapt to that, we will.
It's not just cities being submerged that is problematic. It's the collapse of the corn industry due to rain, so we'll have to find a new industrial-scale source of starch for our chemical needs. It's the infrastructure expense as we have to adapt our inland cities to accommodate the billions of displaced people from the flooded coasts. It's the disaster relief efforts as storms become more energetic. It's the economic calamity as major shipping ports shut down and new ones have to be built, rerouting entire regions of supply chains.
Sure, we can adapt to that... but it's going to be a long, hard, and expensive road to travel. There will be tremendous amounts of human suffering, not lust in hardship and death for those who can't adapt, but in extra work for those that have to carry the bulk of the "adapting" load.
We will reach for the stars, and thanks to our civilization, never have they been closer to our grasp. We will become an interstellar species, and venture out into the heavens. The earth, will continue to do what the earth does, until the sun takes her.
A poignant thought, but far outside our grasp at the moment. There is no other planet in the solar system that we can colonize with current technology, and we definitely don't have the technology to survive as an "interstellar species". The most we can do right now is to fling ourselves off of this planet, and promptly (within a generation or two) die.
We will never come into balance with the earth because the earth was never in balance to begin with. Every era has brought change to the earth, and that won't stop. ... We aren't stupid enough to try is change the earth to keep it constant to the moment of our awakening.
No, we aren't stupid, and that's not the point. Those of us who fight climate change aren't trying to restore any perfect "balance with the earth", or stop the change the next era will bring. We're trying to keep this era, with breathable air and a functioning 4000-year-old society, going for as long as we can. Yes, someday the era will end, and New Orleans will sink, and we'll have to seek refuge among the stars... but our goal is to hold that off as long as possible, and to avoid the high cost of adapting to such catastrophe, as our "literate scientific civilization" continues to advance our technology. If we're successful, then by the time the Florida becomes a reef, we'll already have mature technology allowing our society to easily adapt to the new life.
We aren't hiding in a box. We're facing our species' ongoing battle with death, and we plan to cheat.