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 New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)

nachricht Reusable carbon nanotubes could be the water filter of the future, says RIT study
30.03.2017 | Rochester Institute of Technology

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: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Bare bones: Making bones transparent

27.04.2017 | Life Sciences

Study offers new theoretical approach to describing non-equilibrium phase transitions

27.04.2017 | Physics and Astronomy

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>