For all the carbon capture that the Devonian/Carboniferous period did over 100 million years, humanity undid a large part of it in 150 or so years. And now to preserve human civilisation in some form, the most direct way is probably to rebuild that carbon sink within a much shorter time. Much shorter than 150 years, not 100 million. Current carbon emissions are over 10 billion tonnes per year, so the capture speed wi…
In theory, a sink large enough to bring the Earth back to carbon neutral would be possible if the Sahara were reforested[0]: > The team's calculations suggest the forested deserts could draw down around 8bn tonnes of carbon a year, about the same as emitted from fossil fuels and deforestation today. https://www.theguardian.com/technology/2009/nov/04/forests-d... Edit: > if insoluble carbonates could be synthesised fr…
There's also the very real possibility of forest fires releasing huge amounts of carbon at once. Even dead trees preserved in peat bogs could burn and release carbon in this manner.
Rocks have their own weaknesses such as ocean acidification, but relatively speaking they're much more stable.