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Human-induced greening of the northern extratropical land surface


Significant land greening in the northern extratropical latitudes (NEL) has been documented through satellite observations during the past three decades1,2,3,4,5. This enhanced vegetation growth has broad implications for surface energy, water and carbon budgets, and ecosystem services across multiple scales6,7,8. Discernible human impacts on the Earth’s climate system have been revealed by using statistical frameworks of detection–attribution9,10,11. These impacts, however, were not previously identified on the NEL greening signal, owing to the lack of long-term observational records, possible bias of satellite data, different algorithms used to calculate vegetation greenness, and the lack of suitable simulations from coupled Earth system models (ESMs). Here we have overcome these challenges to attribute recent changes in NEL vegetation activity. We used two 30-year-long remote-sensing-based leaf area index (LAI) data sets12,13, simulations from 19 coupled ESMs with interactive vegetation, and a formal detection and attribution algorithm14,15. Our findings reveal that the observed greening record is consistent with an assumption of anthropogenic forcings, where greenhouse gases play a dominant role, but is not consistent with simulations that include only natural forcings and internal climate variability. These results provide the first clear evidence of a discernible human fingerprint on physiological vegetation changes other than phenology and range shifts11.

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Figure 1: Spatial distribution of LAI trends for 1982–2011.
Figure 2: Observed and simulated 1982–2011 time series of LAI anomalies.
Figure 3: Parameterized frequency distributions of LAI 1982–2011 30-year-long trends.
Figure 4: Results from optimal D&A for 1982–2011 time series of LAI anomalies.

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This work is supported by the Biogeochemistry-Climate Feedbacks Scientific Focus Area project funded through the Regional and Global Climate Modeling Program, and the Terrestrial Ecosystem Science Scientific Focus Area project funded through the Terrestrial Ecosystem Science Program, with additional support from the Accelerated Climate Modeling for Energy project, in the Climate and Environmental Sciences Division (CESD) of the Biological and Environmental Research (BER) Program in the US Department of Energy Office of Science. Oak Ridge National Laboratory is managed by UT-BATTELLE for DOE under contract DE-AC05-00OR22725. This work is supported in part by the Fondation STAE, via the project Chavana. R.S. thanks the H2020 project CRESCENDO ‘Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination and Outreach’, which received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 641816. R.B.M. is supported by NASA Earth Science Division through MODIS and VIIRS grants. B.W. is supported by the National Basic Research Program of China (Grant no. 2014CB441302). P.C. thanks the ERC SyG project IMBALANCE-P Effects of phosphorus limitations on Life, Earth system and Society Grant agreement no. 610028.

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J.M. conceived the study. J.M., A.R., B.Y., X.S., P.E.T. and R.S. performed diagnostics and wrote the text, with comments and edits from all authors.

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Correspondence to Jiafu Mao.

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Mao, J., Ribes, A., Yan, B. et al. Human-induced greening of the northern extratropical land surface. Nature Clim Change 6, 959–963 (2016).

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