A simplified diagram of the contemporary global carbon cycle is shown below, displaying major reservoirs (boxes) and annual fluxes (arrows) in petagrams of carbon per year (Pg C yr−1\text{Pg C yr}^{-1}Pg C yr−1).
Using the data provided in the diagram, calculate the net annual rate of change of the Atmospheric Carbon Pool, and determine how many years it would take to double the atmospheric pool if this rate remains constant. Give both values to an appropriate number of significant figures.
+8.4 Pg C yr−1+8.4\text{ Pg C yr}^{-1}+8.4 Pg C yr−1 and 95 years95\text{ years}95 years
+9.4 Pg C yr−1+9.4\text{ Pg C yr}^{-1}+9.4 Pg C yr−1 and 85 years85\text{ years}85 years
+6.2 Pg C yr−1+6.2\text{ Pg C yr}^{-1}+6.2 Pg C yr−1 and 129 years129\text{ years}129 years
+3.8 Pg C yr−1+3.8\text{ Pg C yr}^{-1}+3.8 Pg C yr−1 and 211 years211\text{ years}211 years