Drought Drives Decade-Long Decline in Plant Growth
WASHINGTON -- Global plant productivity that once was on the rise with
warming temperatures and a lengthened growing season is now on the
decline because of regional drought according to a new study of NASA
satellite data.
Plant productivity is a measure of the rate of the photosynthesis
process that green plants use to convert solar energy, carbon dioxide
and water to sugar, oxygen and eventually plant tissue. Compared with
a 6 percent increase in plant productivity during the 1980s and
1990s, the decline observed over the last decade is only 1 percent.
The shift, however, could impact food security, biofuels and the global carbon cycle.
Researchers Maosheng Zhao and Steven Running of the University of
Montana in Missoula discovered the global shift from an analysis of
NASA satellite data. The discovery comes from an analysis of plant
productivity data from the Moderate Resolution Imaging
Spectroradiometer on NASA's Terra satellite, combined with other
growing season climate data, including temperature, solar radiation and water.
"We see this as a bit of a surprise, and potentially significant on a
policy level because previous interpretations suggested global
warming might actually help plant growth around the world," Running said.
Previous research found land plant productivity was on the rise. A
2003 paper in the journal Science led by scientist Ramakrishna
Nemani, now a researcher at NASA's Ames Research Center in Moffett
Field, Calif., showed the 6 percent increase in global terrestrial
plant productivity between 1982 and 1999. The increase was traced to
nearly two decades of temperature, solar radiation and water
availability conditions, influenced by climate change, that were
favorable for plant growth.
Setting out to update that analysis, Zhao and Running expected to see
similar results as global average temperatures continued to climb.
Instead, they found the negative impact of regional drought
overwhelmed the positive influence of a longer growing season,
driving down global plant productivity between 2000 and 2009. The
team published its findings Thursday in Science.
"This is a pretty serious warning that warmer temperatures are not
going to endlessly improve plant growth," Running said.
Zhao and Running's analysis showed that since 2000, high-latitude
Northern Hemisphere ecosystems have continued to benefit from warmer
temperatures and a longer growing season. But that effect was offset
by warming-associated drought that limited growth in the Southern
Hemisphere, resulting in a net global loss of land productivity.
"This past decade's net decline in terrestrial productivity
illustrates that a complex interplay between temperature, rainfall,
cloudiness, and carbon dioxide, probably in combination with other
factors such as nutrients and land management, will determine future
patterns and trends in productivity," said Diane Wickland, program
manager of the Terrestrial Ecology research program at NASA
Headquarters in Washington.
Researchers want to continue monitoring these trends in the future
because plant productivity is linked to shifting levels of greenhouse
gas carbon dioxide in the atmosphere and stresses on plant growth
that could challenge food production.
"Even if the declining trend of the past decade does not continue,
managing forests and crop lands for multiple benefits to include food
production, biofuel harvest, and carbon storage may become
exceedingly challenging in light of the possible impacts of such
decadal-scale changes," Wickland said.
For information and video about this new research, visit:
http://www.nasa.gov/topics/
Source: NASA
