Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

NASA-Funded Study Refutes Alarmist Claims Of Drought Driven Declines In Plant Productivity And Risks To Global Food Security

29.08.2011
A new, comprehensive study by an international team of scientists, including scientists at Boston University in the US and the Universities of Viçosa and Campinas in Brazil, has been published in the current issue of Science (August 26, 2011) refuting earlier alarmist claims that drought has induced a decline in global plant productivity during the past decade and posed a threat to global food security.

Those earlier findings published by Zhao and Running in the August 2010 issue of Science (Vol. 329, p. 940) also warned of potentially serious consequences for biofuel production and the global carbon cycle. The two new technical comments in Science contest these claims on the basis of new evidence from NASA satellite data, which indicates that Zhao and Running’s findings resulted from several modeling errors, use of corrupted satellite data and statistically insignificant trends.

The main premise of Zhao and Running’s model-based study was an expectation of increased global plant productivity during the 2000s based on previously observed increases during the 1980s and 1990s under supposedly similar, favorable climatic conditions. Instead, Zhao and Running were surprised to see a decline, which they attributed it to large-scale droughts in the Southern Hemisphere.

“Their model has been tuned to predict lower productivity even for very small increases in temperature. Not surprisingly, their results were preordained,” said Arindam Samanta, the study’s lead author. (Samanta, now at Atmospheric and Environmental Research Inc., Lexington, MA, worked on the study as a graduate student at Boston University’s Department of Geography and Environment.)

Zhao and Running’s predictions of trends and year-to-year variability were largely based on simulated changes in the productivity of tropical forests, especially the Amazonian rainforests. However, according to the new study, their model failed miserably when tested against comparable ground measurements collected in these forests.

“The large (28%) disagreement between the model’s predictions and ground truth imbues very little confidence in Zhao and Running’s results,” said Marcos Costa, coauthor, Professor of Agricultural Engineering at the Federal University of Viçosa and Coordinator of Global Change Research at the Ministry of Science and Technology, Brazil.

This new study also found that the model actually predicted increased productivity during droughts, compared to field measurements, and decreased productivity in non-drought years 2006 and 2007 in the Amazon, in contradiction to the main finding of the previous report. “Such erratic behavior is typical of their poorly formulated model, which lacks explicit soil moisture dynamics,” said Edson Nunes, coauthor and researcher at the Federal University of Viçosa, Brazil.

The new study indicates that Zhao and Running used NASA’s MODIS satellite data products, such as vegetation leaf area, without paying caution to data corruption by clouds and aerosols. “Analyzing the same satellite data products after carefully filtering out cloud and aerosol-corrupted data, we could not reproduce the patterns published by Zhao and Running. Moreover, none of their reported productivity trends are statistically significant,” said Liang Xu, coauthor and graduate student at Boston University.

In any case, the trends in plant productivity reported by Zhao and Running are miniscule—a 0.34% reduction in the Southern Hemisphere offset by a 0.24% gain in the Northern Hemisphere for a net decline of 0.1% over a ten-year period from 2000 to 2009. “This is the proverbial needle in a haystack,” said Simone Vieira, coauthor and researcher at the State University of Campinas, Brazil. “There is no model accurate enough to predict such minute changes over such short time intervals, even at hemispheric scales.”

Any investigation of trends in plant growth requires not only consistent and accurate climate and satellite data but also a model suitable for such purposes. “The Zhao and Running study does not even come close,” said Ranga Myneni, senior author and Professor of Geography, Boston University. “Their analysis of satellite data is flawed because they included poor quality data and do not bother to test trends for statistically significance. Our analyses of four different higher-quality MODIS satellite vegetation products that have been carefully filtered for data corruption show no statistically significant trends over 85% of the global vegetated lands.”

This study was funded through a research grant by the NASA MODIS project to Prof. Myneni for investigation on the use of MODIS satellite data to study vegetation on our planet.

Experts to comment on this story:
Prof. Ian Colin Prentice, Macquarie University, colin.prentice@mq.edu.au, +61-425-040669
Dr. Compton J. Tucker, NASA, compton.j.tucker@nasa.gov, +1-301-614-6644
Prof. Inez Fung, UC-Berkeley, ifung@berkeley.edu, +1-510-643-9367
About Boston University—Founded in 1839, Boston University is an internationally recognized private research university with more than 30,000 students participating in undergraduate, graduate, and professional programs. As Boston University’s largest academic division, the College and Graduate School of Arts & Sciences is the heart of the BU experience with a global reach that enhances the University’s reputation for teaching and research.
Ranga Myneni: ranga.myneni@gmail.com, +1-617-470-7065
Arindam Samanta: arindam.sam@gmail.com, +1-617-852-5256
Marcos Costa: mhcosta@ufv.br, +55-31-8727-1899

Ranga Myneni | Newswise Science News
Further information:
http://www.bu.edu

More articles from Studies and Analyses:

nachricht Amputees can learn to control a robotic arm with their minds
28.11.2017 | University of Chicago Medical Center

nachricht The importance of biodiversity in forests could increase due to climate change
17.11.2017 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig

All articles from Studies and Analyses >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Long-lived storage of a photonic qubit for worldwide teleportation

12.12.2017 | Physics and Astronomy

Multi-year submarine-canyon study challenges textbook theories about turbidity currents

12.12.2017 | Earth Sciences

Electromagnetic water cloak eliminates drag and wake

12.12.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>