[wat10000]

A 2-10% increase seems like a hell of a lot.

Human CO2 emissions are well under 10% of natural CO2 emissions, and yet that additional amount has been enough to increase the atmospheric concentration of CO2 by over 50% and substantially alter the planetary climate.

CO2 in the atmosphere is at a vastly larger scale than mass falling in from space, so that doesn't mean this is a problem, but that percentage certainly seems to indicate that the question should be studied further.