![]() From 1901 to 2010 GPP has increased globally (Fig. Model-based reconstructions indicate significant changes in gross uptake of carbon by the vegetated land surface over the 20 th Century. ![]() This is based on the emulation (see Methods) of MsTMIP where only climate varies and then sequentially retrieving the contribution of each climatic factor by simulation differencing 9.Įnhanced GPP is the basis by which land ecosystems buffer climate change. We also use machine learning to recover the change in GPP for the individual offline climatic factors of heat (near-surface air temperature), water (precipitation), and light (downwelling shortwave radiation). 11) and (2) an 13-member ensemble of fully coupled ESMs from CMIP5, the fifth phase of the Coupled Model Intercomparison Project 12. Our approach uses two broad ensembles of Earth system models (ESMs): (1) a 11-member ensemble of observation-driven land surface models-corresponding to the land component of ESMs in offline mode-from the Multi-scale synthesis and Terrestrial Model Intercomparison Project (MsTMIP) (ref. We quantify changes in GPP due to natural climate variability, land use/land cover change, greenhouse gases, and nitrogen deposition. GPP is of central importance for the net carbon balance as it represents the entry of carbon into land ecosystems such that all other processes are downstream. Here we use a novel dual constraint approach to attribute centennial scale changes in GPP at grid cell to global scales. This suggests that an improved understanding of the net land-atmosphere CO 2 signal can be achieved by examining each component flux, and relevant drivers of change, individually. While this quantity is important to inform climate policy, e.g., Paris Climate Accords, it is the disequilibrium across many processes-such as heterotrophic respiration and fire emissions-with uncertain magnitude and spatiotemporal patterns 7, 9, 10. For land carbon metabolism, attribution typically focuses on net land uptake of CO 2 (ref. Model-based attribution, quantifying the importance and magnitude of causal factors for a detected change 3, is routinely used to assess the relative contributions of anthropogenic factors and natural variability on Earth system phenomena, ranging from precipitation extremes to decadal-scale changes in net carbon uptake 4– 8. Our understanding of changes in Earth system processes depends on models 1, 2. 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. Third, changes in climate have functioned as fertilization to enhance GPP (1.4 Pg C per annum in the 2001 decade). Second, CO 2 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. First, anthropogenic controls on GPP change have increased from 57% (1901 decade) to 94% (2001 decade) of the vegetated land surface. Our dual constraint attribution approach provides three insights into the spatiotemporal patterns of GPP change. Here we show that 1901 to 2010 changes in GPP have been dominated by anthropogenic activity. 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. ![]() This 119 Pg C per annum transfer of CO 2 into plants-gross primary productivity (GPP)-is the largest land carbon flux globally. Terrestrial vegetation removes CO 2 from the atmosphere an important climate regulation service that slows global warming. ![]()
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