> Actively remove greenhouse gasses from atmosphere. Will need to do that, but land use and dirty energy trends away from net negative. Also, it’s a 100 year project once started.

I once did the math, assuming we have enough resources to build a lot of solar panels. Assuming current efficiency levels of solar panels and current commercial feasible levels of direct air carbon capture (DAC), if we annually allocated an amount equal to our current annual solar panel production to building large solar farms dedicated to powering DAC plants, in about 150ish years those plants would be capturing each year an amount about equal to our current total annual emissions.

If we keep expanding solar panel production we could shorten that timeline and build more than just enough to breakeven. The area for those solar farms would be about 1/15th the area of the 5 largest subtropical deserts.

What would we do with all the carbon extracted? That's not really a problem. If we can't think of a good use for it, just mount the solar panels powering the DAC plants a few meters off the ground, convert the carbon to graphite, and dump it under the solar panels. Spread evenly it would only be a few mm thick.