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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Human-induced greening of the northern extratropical land surface

Jiafu Mao
Oak Ridge National Laboratory

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06/23/2016
Understanding and attributing multiyear trends of vegetation growth in the northern-extratropical latitudes (NEL).

The Science                       
This study examines Leaf Area Index (LAI, area of leaves per area of ground) during the growing season (April-October) over the NEL (30°–75°N). Previous work assessing modeled and observed LAI has focused on timing of seasonal growth, interannual variability, and multiyear trends. Earlier studies showed that spatiotemporal changes in LAI were related to variation in climate drivers (mainly temperature and precipitation). This study adds to an increasing body of evidence that NEL has experienced an enhancement of vegetation activity, as reflected by increased trends in vegetation indices, aboveground vegetation biomass, and terrestrial carbon fluxes during the satellite era. Our analysis goes beyond previous studies by using formal detection and attribution methods to establish that the trend of increased northern vegetation greening is clearly distinguishable from both internal climate variability and the response to natural forcings alone. It can be rigorously attributed, with high statistical confidence, to anthropogenic forcings, particularly to rising atmospheric concentrations of greenhouse gases.

The Impact
Our work demonstrates the first clear evidence of a discernible human fingerprint on NEL physiological vegetation changes, and propose new investigations which could use detection and attribution methods to study broad-scale terrestrial ecosystem dynamics.

Summary
Contacts (BER PM)
Renu Joseph, Daniel Stover and Jared DeForest
renu.joseph@science.doe.gov (301-903-9237), Daniel.Stover@science.doe.gov (301-903-0289), and Jared.DeForest@science.doe.gov (301-903-1678)
PI Contact
Jiafu Mao: Environmental Sciences Division and Climate Change Science Institute, Oak Ridge National Laboratory, maoj@ornl.gov (865-576-7815)

Funding
J. Mao, X. Shi, P.E. Thornton, D.M. Ricciuto, and F.M. Hoffman are supported by DOE Office of Science, Biological and Environmental Research, including support from the following programs: Regional and Global Climate Modeling Program (ORNL BGC-Feedbacks SFA); Terrestrial Ecosystem Science Program (ORNL TES SFA); Earth System Modeling (ACME project).

Publications
Jiafu Mao*, Aurélien Ribes, Binyan Yan, Xiaoying Shi, Peter E. Thornton, Roland Séférian, Philippe Ciais, Ranga B. Myneni, Hervé Douville, Shilong Piao, Zaichun Zhu, Robert E. Dickinson, Yongjiu Dai, Daniel M. Ricciuto, Mingzhou Jin, Forrest M. Hoffman, Bin Wang, Mengtian Huang, and Xu Lian, 2016. Human-induced greening of the northern extratropical land surface. Nature Climate Change, 10.1038/nclimate3056.

ORNL TES-SFA, Feedbacks SFA, ACME


Spatial distribution of LAI trends observed by satellite and simulated by CMIP5 models over the  period  1982–2011. Source: J. Mao, used by permission.

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