Cumulative CO2 emissions in the 50 years since 1965
The residence time of CO2 in the atmosphere is about 5 – 10 years. The CO2 burden for which man-kind can be responsible extra CO2 is absorbed by improving the growth of all plant life and is quickly resorbed by the oceans.
This is a simplistic view, the whole question of the various Carbon cycles is well covered by Clive Best here:
The following graphs shown 5 and 10 year half-life calculations.
These graphs show that on both an 5 year and 10 year half-life basis Chinese CO2 emissions have already surpassed the USA. And that on a 5 year half-life basis the 160 nations of the underdeveloped world are approaching the cumulative emissions of the EU(28).
When the cumulative 5 years half-life CO2 emissions / head are plotted the significant decline in the USA arising from the growing use of fracked gas for electricity generation becomes clear.