This manuscript can now be published - it's a very nice review. I suggest to take also these comments into account when producing the final manuscript:

p19 l 35: what means "constrain" here quantitatively? Can you state an uncertainty?

Radiocarbon section: the bomb-produced 14C really began in 1955 (not in the 1940's). As to using radiocarbon for the estimation of fossil fuel emissions, there is also the complication induced by the 14C emissions from nuclear reactors and nuclear reactor fuel processing plants (e.g. Graven and Gruber, 2011). This might be mentioned here.

Ethane section: Biomass burning also contributes substantial ethane (Methane/Ethane ratio of about 8, see e.g. Aydin et al, 2011)