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Saturday, August 21, 2010

Earth's global plant yields decline due to increased global temperatures

Earth's plant yields decline despite global warming

by Balasubramanyam Seshan, International Business Times, August 20, 2010

Earth's plant productivity, which has been stimulated by global warming, has declined due to regional drought despite the rise in temperatures and a lengthened growing season, according to NASA satellite data.

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 research was supported by NASA and the National Oceanic and Atmospheric Administration (NOAA).

Plant output 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.

The decline in plant productivity observed over the last decade is only 1%, compared with a 6% increase during the 1980s and 1990s. However, the shift could impact food security, biofuels and the global carbon cycle, the researchers say.

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. This is a pretty serious warning that warmer temperatures are not going to endlessly improve plant growth,” said Steven Running.

For example, growth is generally limited in high latitudes by temperature and in deserts by water. But regional limitations can vary in their degree of impact on growth throughout the growing season, the researchers say.

The analysis showed that since 2000, high-latitude Northern Hemisphere ecosystems have continued to benefit from warmer temperatures and a longer growing season but this was offset by warming-associated drought that limited growth in the Southern Hemisphere, resulting in a net global loss of land productivity.

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.

A previous research had found global terrestrial plant productivity was on the rise, showing a 6% increase 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, Maosheng Zhao and Steven Running expected to see similar results as global average temperatures continued to climb. Instead, the researchers found that the negative impact of regional drought overwhelmed the positive influence of a longer growing season, driving down global plant productivity between 2000 and 2009.
“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,” said Diane Wickland, program manager of the Terrestrial Ecology research program at NASA Headquarters in Washington.

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