A new, comprehensive study by an international team of scientists, including scientists at Boston University in the US and the Universities of Viosa 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 teste
|Contact: Patrick Farrell|