NASA refutes declines in plant productivity, global food security

A new, comprehensive study by an international team of scientists…has been published in the current issue of Science 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 also warned of potentially serious consequences for biofuel production and the global carbon cycle…

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…

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…

None of their reported productivity trends are statistically significant,” said Liang Xu, coauthor…

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…”There is no model accurate enough to predict such minute changes over such short time intervals, even at hemispheric scales…”

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.”

I realize most folks only notice studies like these when they show up in the popular press. Those articles bear their own special circumstances and problems. Veracity isn’t often a required quality.

I couldn’t stop my smile when I bumped into this – because what we’re witnessing is the peer-reviewed scientific equivalent of a barroom brawl. You don’t get to hear the shouting and bottles breaking. But, believe me, emotions are running just as high.

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