National Aeronautics and Space Administration Jet Propulsion Laboratory
National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Modeling suggests fossil fuel emissions have been driving increased land carbon uptake since the turn of the 20 th Century Early 2000 s Background: Climate regulation is a free ecosystem service provided by healthy intact vegetation. This service acts to slow down global change by removing roughly 25% of carbon dioxide emissions each year. However, what has driven the historical increase in photosynthesis on land has been poorly understood. We assessed 24 different land climate models to reconstruct historical changes in photosynthesis from 1901 to 2010 globally. 1901 -2010 Results: From the perspective of the land carbon cycle, the Anthropocene started in the early 1900 s. The Anthropocene denotes an era where humanity is the dominant driver of change in the Earth system. The reasons for this are the increases in the amount of CO 2—from fossil fuel use—and reactive nitrogen—from pollution and farming—in the atmosphere. Contrary to expectations, increases in temperature have also acted to increase photosynthesis. Figure 1 (above) Land area where human-caused factors drive changes in photosynthesis (brown) has increased from 57% (early 1900 s) to 94% (early 2000 s). (below) Over the 20 th Century this is largely driven by fossil fuel use (blue) as well as nitrogen addition (green). Schwalm, C. R. , et al. , 2020. Modeling suggests fossil fuel emissions have been driving increased land carbon uptake since the turn of the 20 th Century. Scientific Reports 10(9059). Significance: Our findings suggest that global change drivers have allowed photosynthesis to keep pace with anthropogenic change. The extent to which these same factors will prolong, degrade or ultimately reverse the ecosystem service of climate regulation is unclear. Overall, this analysis highlights the use of modeling to understand discrete factors that drive changes in carbon cycling and uncertainty on the viability of future climate regulation. This work was supported in part by NASA programs: ABo. VE, CARBON, CMS, IDS, and INCA.
National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Contact: Joshua B. Fisher, 233 -305 C, Jet Propulsion Laboratory, Pasadena, CA 91109 jbfisher@jpl. nasa. gov Citation: Schwalm, C. R. , et al. , 2020. Modeling suggests fossil fuel emissions have been driving increased land carbon uptake since the turn of the 20 th Century. Scientific Reports 10(9059): 1 -9. Data Sources: • We used data from 11 terrestrial biosphere simulators from the Multi-scale synthesis and Terrestrial Model Intercomparison Project (Ms. TMIP Version 1). • We used data from 13 earth system models from CMIP 5, the fifth phase of the Coupled Model Intercomparison Project. Technical Description of Figure: • Global map of changes in gross primary productivity (GPP) due to anthropogenic factors. Values calculated as the ratio of absolute values of anthropogenic to natural forcing-induced changes in GPP using CMIP 5 models only. A ratio greater than unity (brown) indicates that anthropogenic forcings (primarily well-mixed greenhouse gases) dominate; whereas green indicates natural forcings (solar irradiance and volcanic aerosols) dominate. • Global map of change drivers in gross primary productivity (GPP). Spatial long-term mean (1901 -2010) changes in GPP due to climate (cyan), land use and land cover change (LULCC, yellow), CO 2 fertilization (blue), and nitrogen deposition (green) using Ms. TMIP models only. Scientific significance, societal relevance, and relationships to future missions: Our study is model-based attribution where we attribute changes in GPP from 1901 to 2010 to climate, LULCC, [CO 2], nitrogen deposition, air temperature, precipitation, and shortwave radiation as well as natural vs. anthropogenic forcings. We find a clear fingerprint of anthropogenic forcings in global land carbon cycling starting in 1901. For at least the past century the global carbon cycle is majority controlled by human action. Although models (offline and fully-coupled) show a secular increase (both past and future) in land carbon uptake due to CO 2 fertilization and nitrogen subsidy, empirical evidence for this is mixed. Future satellite missions targeting ecosystem function, for example, may help resolve the effect sizes of individual factors by providing nowcast attribution at scale to complement model-based attribution, existing missions and experimental manipulations. These results may help
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