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.