Global Plant Productivity
Of the few things that looked advantageous regarding global warming, one of those included longer growing seasons and the ability of plants and crops to grow more in a warmer environment, that was richer in CO2. A new study by NASA shows that the idea that plant productivity would increase, if only temporarily for an extended period of time, with increased concentrations of carbon dioxide (CO2), and longer growing seasons, is now at risk. Current data suggests a slight decrease in global plant productivity.
At this early stage of global warming, this news is disturbing because it indicates that we can not rely on increased productivity in the agriculture sector, and the carbon sink will not hold as much CO2, as expected.
This global plant productivity is often referred to as the Net Primary Production (NPP), which is how much CO2 vegetation takes in during photosynthesis minus how much CO2 the plants release during respiration (metabolizing sugars and starches for energy) or decay.
The NPP had been showing increases in the 80's and 90's of around 6%. When researchers decided to update the study, they found something unexpected. A decrease, -1%. This slight decrease reminds us that the earth, as a system of systems, is non-linear and has many dynamic interactions between the related sub and parent systems that are the make-up of our world. However, it is important to note that this change seems to be related to drought and fire 'trends', which are indicted, and expected, to be a product of global warming.
Note: This report apparently includes data into 2009. It will be interesting to see when the 2010 data is added to the assessment. At least from a social perspective, we will see the relationship between the headlines and the NPP drop due to fires, floods and droughts (see Aug 'Leading Edge').
Drought Drives Decade-Long Decline in Plant Growth
Earth has done an ecological about-face: Global plant productivity that once flourished under warming temperatures and a lengthened growing season is now on the decline, struck by the stress of drought.
NASA-funded researchers Maosheng Zhao and Steven Running, of the University of Montana in Missoula, discovered the global shift during an analysis of NASA satellite data. Compared with a six-percent increase spanning two earlier decades, the recent ten-year decline is slight -- just one percent. The shift, however, could impact food security, biofuels, and the global carbon cycle.
"We see this as a bit of a surprise, and potentially significant on a policy level because previous interpretations suggested that global warming might actually help plant growth around the world," Running said.
"These results are extraordinarily significant because they show that the global net effect of climatic warming on the productivity of terrestrial vegetation need not be positive -- as was documented for the 1980’s and 1990’s," said Diane Wickland, of NASA Headquarters and manager of NASA's Terrestrial Ecology research program. Conventional wisdom based on previous research held that land plant productivity was on the rise. A 2003 paper in Science led by then University of Montana scientist Ramakrishna Nemani (now at NASA Ames Research Center, Moffett Field, Calif.) showed that global terrestrial plant productivity increased as much as six percent between 1982 and 1999. That's because for nearly two decades, temperature, solar radiation and water availability -- influenced by climate change -- were favorable for growth.
Setting out to update that analysis, Zhao and Running expected to see similar results as global average temperatures have continued to climb. Instead, they found that the 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 their findings Aug. 20 in Science.
"This is a pretty serious warning that warmer temperatures are not going to endlessly improve plant growth," Running said.