Higher Temperatures Lessen Plants' Ability to Store CO2
Lauren Morello and Climatewire
Rising temperatures have helped blunt plants' ability to pull carbon from the atmosphere, according to a study published yesterday in Science.
The amount of carbon soaked up by Earth's plants and trees fell by roughly 1 percent, or 550 million metric tons, between 2000 and 2009.
Researchers at the University of Montana say that global warming, large-scale droughts and an overall drying trend in the Southern Hemisphere contributed to the drop.
Warmer temperatures did lengthen growing seasons in high northern regions, but that wasn't enough to counteract the effect of changes in Earth's water cycle.
The scientists based their findings on information gathered by a NASA satellite as well as meteorological data.
Authors Maosheng Zhao and Steven Running, both ecologists, were surprised by their results, Zhao said.
That's largely because Running contributed to a study published in 2003 that found the amount of carbon taken up by plants increased between 1982 and 1999, a time period during which temperatures rose and the amount of carbon dioxide in the atmosphere grew.
A 'gloomy' future?
"We expected that net primary productivity would increase," Zhao said. "However, after we analyzed our data from 2002 to 2009, we found instead of increasing, NPP showed a reduced trend."
Zhao added, "It's this drought and drying that caused the decrease."
Overall, plants and trees absorb about half of CO2 emissions produced by burning fossil fuels. The world's oceans take up the rest.
But the new study suggests that might be changing, with consequences for global food security and biofuel production.
"We don't know what will happen in the future," Zhao said. "But many models estimate that in the future, droughts will become more frequent. So based on that, we expect the future will be gloomy."
AUG. 20 2010
www.scientificamerican.com/article.cfm