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Terrestrial Gross Primary Productivity Increased by 31 Percent Over the Past Century

Paper Reviewed
Campbell, J.E., Berry, J.A., Seibt, U., Smith, S.J., Montzka, S.A., Launois, T., Belviso, S., Bopp, L. and Laine, M. 2017. Large historical growth in global terrestrial gross primary production. Nature 544: 84-87.

In a recent review we documented the work of Cheng et al. (2017), who utilized a combination of ground-based and remotely-sensed land and atmospheric observations to estimate changes in global gross primary production (GPP) over the period 1982 to 2011. In that work, Cheng et al. calculated that Earth's terrestrial GPP has increased by 0.83 ± 0.26 Pg C per year, or a total of 24.9 Pg C over the past three decades. Furthermore, they determined that a 10% increase in atmospheric CO2 induces an approximate 8% increase in global GPP. Now, following on the heels of that important study is the equally intriguing work of Campbell et al. (2017), who present similar -- though independent -- findings of a 20th-century enhancement in terrestrial GPP of 31 percent.

In reaching this figure, Campbell et al. analyzed long-term atmospheric carbonyl sulfide (COS) records derived from Antarctic ice-core, firn and ambient air samples, which history they contend "is a good proxy for the total [global] atmospheric burden of COS." Their approach was based on the relationship that exists between terrestrial plant uptake of COS through a process that is related to photosynthesis; and they maintain that this process is dominant "at annual and continental scales." Then, they interpreted the COS records "using a model that simulates changes in COS concentration according to changes in its sources and sinks-including a large sink that is related to GPP." And in doing so, the team of seven scientists found that "the optimal value of GPP growth from these simulations was 31%," which they say is "at the high end of the historical range of +5% to +34% used in global carbon/climate models, providing a new global estimate of this largely unconstrained process."

It is interesting to note that the 31% increase in global GPP calculated by Campbell et al. is very similar to the independent calculation of Cheng et al. For in utilizing Cheng et al.'s relationship that they derived between GPP and atmospheric CO2 (i.e., that a 10% increase in atmospheric CO2 induces an approximate 8% increase in global GPP), one can calculate that the 40% increase in atmospheric CO2 during the modern era should have enhanced global terrestrial GPP by 32%. Thus, we have two independent findings from two independent scientific teams confirming there has been a large increase in global GPP since the beginning of the Industrial Revolution. And from the additional work of Cheng et al., we know that that increase has largely resulted from the growth-enhancing, water-saving and stress-alleviating benefits of atmospheric CO2 fertilization of plants.

Cheng, L., Zhang, L., Wang, Y.-P., Canadell, J.G., Chiew, F.H.S., Beringer, J., Li, L., Miralles, D.G., Piao, S. and Zhang, Y. 2017. Recent increases in terrestrial carbon uptake at little cost to the water cycle. Nature Communications 8: 110, DOI:10.1038/s41467-017-00114-5.

Posted 25 October 2017