Christopher R. Schwalm, Deborah N. Huntinzger, Anna M. Michalak, Kevin Schaefer, Joshua B. Fisher, Yuanyuan Fang & Yaxing Wei
Through photosynthesis, terrestrial vegetation absorbs a substantial fraction of carbon released into the atmosphere as a result of fossil fuel burning and land use change. This movement of carbon from the atmosphere, termed gross primary productivity (GPP), thereby slows global warming. To manage global warming, it is therefore necessary to understand changes in GPP. In this work, we examine drivers of these changes, and find 1) human activities dominated changes in GPP between 1901 and 2010, 2) the most important drivers of those changes are CO2 fertilization and nitrogen deposition, and 3) climate changes have enhanced GPP. Our findings suggest human activity became the dominant influence on Earth’s environment and climate more than 100 years ago, and drivers of global change have allowed GPP to keep pace with human-associated carbon emissions.
Figure: Spatial pattern of changes in gross primary productivity (GPP) due to anthropogenic forcings. (a), Map of 1901 decade. (b), Map of 2002 decade. Areal extent of GPP change due to anthropogenic forcings: 57% and 94% for 1901 and 2001 decades respectively. Values calculated as the ratio of absolute values of anthropogenic to natural forcing-induced changes in GPP using CMIP5 models only (see Methods). A ratio greater than unity (brown) indicates that anthropogenic forcings (primarily well-mixed greenhouse gases) dominate; whereas green indictes natural forcings (solar irradiance and volcanic aerosols) dominate. Figure created in Matlab version R2019a 9 (http://www.mathworks.com/products/matlab/).
Terrestrial vegetation removes CO2 from the atmosphere; an important climate regulation service that slows global warming. This 119 Pg C per annum transfer of CO2 into plants—gross primary productivity (GPP)—is the largest land carbon flux globally. While understanding past and anticipated future GPP changes is necessary to support carbon management, the factors driving long-term changes in GPP are largely unknown. Here we show that 1901 to 2010 changes in GPP have been dominated by anthropogenic activity. Our dual constraint attribution approach provides three insights into the spatiotemporal patterns of GPP change. First, anthropogenic controls on GPP change have increased from 57% (1901 decade) to 94% (2001 decade) of the vegetated land surface. Second, CO2 fertilization and nitro gen deposition are the most important drivers of change, 19.8 and 11.1 Pg C per annum (2001 decade) respectively, especially in the tropics and industrialized areas since the 1970’s. Third, changes in climate have functioned as fertilization to enhance GPP (1.4 Pg C per annum in the 2001 decade). These findings suggest that, from a land carbon balance perspective, the Anthropocene began over 100 years ago and that global change drivers have allowed GPP uptake to keep pace with anthropogenic emissions.
Schwalm, C.R., D.N. Huntinzger, A.M. Michalak, K. Schaefer, J.B. Fisher, Y. Fang, Y. Wei (2020) "Modeling suggests fossil fuel emissions have been driving increased land carbon uptake since the turn of the 20th Century," Scientific Reports, 10 (9059), doi:10.1038/s41598-020-66103-9.