Climate Study Finds Human Fingerprint in Northern Hemisphere

New analysis uses detection and attribution methods to establish multiyear trends of vegetation growth in northern-extratropical latitudes.

Image courtesy of Oak Ridge National Laboratory

The spatial distribution of leaf area index trends (m2/m2/30 year) are shown in the growing season (April–October) during the period of 1982–2011 in the mean of satellite observations (top), Earth system model (ESM) simulations with natural forcings alone (lower left), and ESM simulations with combined anthropogenic and natural forcings (lower right).

The Science

For the first time, scientists have been able to examine the effects of natural climate variability versus anthropogenic effects on enhanced plant growth in the northern mid-latitudes within the Earth system models. They found a positive connection between anthropogenic activity and enhanced plant growth. Increased growth can harm water availability and crop growth. The team studied the area of leaves per area of ground during the growing season (April-October) over northern-extratropical latitudes. This area starts at roughly the Tropic of Cancer, a latitudinal line that passes, among other places, through Egypt, India, and Mexico. The area ends above the Arctic Circle. They found that the greening could be rigorously attributed to anthropogenic forcings, in particular to concentrations of greenhouse gases.

The Impact

This work presents the first clear evidence of a discernible of human influence on plant changes in northern latitudes, offering insights into our world. The team used advanced techniques known as fingerprinting to examine plant growth and arrive at this conclusion. This work paves the way for using fingerprinting in broad-scale terrestrial ecosystem dynamics.

Summary

Significant northern-extratropical latitude (30 to 75 degrees north) land greening has been documented through satellite observations during the past three decades. This enhanced vegetation growth has broad implications for surface energy, water, and carbon budgets. The growth also influences ecosystem services across multiple scales. Discernable impacts on Earth’s climate system have been revealed by using statistical frameworks of detection and attribution. These impacts, however, were not previously identified on the northern-extratropical latitude greening signal. The impacts were not identified due to the lack of long-term observational records, possible bias of satellite data, different algorithms used to calculate vegetation greenness, and lack of suitable simulations from coupled Earth system models. Researchers, led by Oak Ridge National Laboratory, overcame these challenges to attribute recent changes in northern-extratropical latitude vegetation activity. They used two recently available 30-year-long, remote-sensing-based leaf area index datasets (area of leaves per area of ground), simulations from 19 coupled Earth system models with interactive vegetation, and a formal detection and attribution algorithm. Their findings reveal that the observed greening record is consistent with an assumption of anthropogenic forcings. The findings are not consistent with simulations that include only natural forcings and internal climate variability. This evidence of historical, human-induced greening in the northern extratropics has implications for both intended and unintended consequences of human interactions with terrestrial ecosystems and the climate system.

Contact

(BER PM)
Renu Joseph
renu.joseph@science.doe.gov (301-903-9237)

Daniel Stover
Daniel.Stover@science.doe.gov (301-903-0289)

Jared DeForest
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

Support for this work was provided by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research (BER), including support from the following BER programs:

  • Regional and Global Climate Modeling [Oak Ridge National Laboratory (ORNL) Biogeochemical-Feedbacks Scientific Focus Area (SFA)]
  • Terrestrial Ecosystem Science (ORNL TES SFA)
  • Earth System Modeling (Accelerated Climate Modeling for Energy)

Publications

J. Mao, A. Ribes, B. Yan, X. Shi, P.E. Thornton, R. Séférian, P. Ciais, R.B. Myneni, H. Douville, S. Piao, Z. Zhu, R.E. Dickinson, Y. Dai, D.M. Ricciuto, M. Jin, F.M. Hoffman, B. Wang, M. Huang, and X. Lian, “Human-induced greening of the northern extratropical land surface.” Nature Climate Change 6(10), 959-63 (2016). [DOI: 10.1038/nclimate3056]

Related Links

Physorg.org article: Climate study finds human fingerprint in Northern Hemisphere greening

Highlight Categories

Program: BER , CESD

Performer: DOE Laboratory