Ask HN: Are there dangers from too much carbon sequestration?

There is a popular thread where HN itself is looking to fund carbon sequestration on a massive scale to stop global warming. The idea is that if global warming goes too far it will take our planet out of equilibrium and become irreversible, so we should actively remove carbon from the atmosphere. The first suggestion was genetically engineering phytoplankton to store carbon in a form that would be less available. In a situation like that, once done we could not undo that. My question is, would there be anything bad that would happen if we had basically runaway carbon sequestration?