Diamond-based molecular nanotechnology, combined with fusion and high efficiency solar as sources of power will make all of our technology and infrastructure carbon sinks. By the end of this century I expect we will be concerned about CO2 going too low and causing a glacial period.

PS Mercury is too far in-system to be that useful. It takes less energy to get to/from the outer planets than it does Mercury. The cold traps on the poles are interesting though--mercury potentially has all the raw material needed for a self-sufficient industrial colony.