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Boston, Mass. — Researchers from Boston University and NASA have recently discovered that parts of the northern hemisphere have become much greener and the growing season has increased over the past 21 years. By using satellite data in correlation with temperature data from thousands of meteorological stations on North America and Eurasia, the researchers have confirmed that plant life above 40 degrees north latitude, from New York to Madrid to Beijing, has been growing more vigorously since 1981 because of rising temperatures and a buildup of greenhouse gases.
“This is an important finding because of possible implications to the global carbon cycle,” says Myneni, associate professor of geography at Boston University. “Carbon dioxide is a main greenhouse gas and is thought to play a major role in rising global temperatures. Under the Kyoto protocol, most of the developed countries in the north can use certain vegetation carbon sinks to meet their greenhouse gas emissions reduction commitments. If the northern forests are greening, they may already be absorbing carbon.”
These results will appear in the September 16 issue of the Journal of Geophysical Research – Atmospheres, published by the American Geophysical Union (AGU). The authors are Liming Zhou, Robert Kaufmann, Nikolai Shabanov and Ranga Myneni of Boston University, and Daniel Slayback and Compton Tucker of NASA’s Goddard Space Flight Center in Greenbelt, Md.
The Eurasian greening was especially persistent over a broad contiguous swath of land from central Europe through Siberia to far-east Russia, where most of the vegetation is forests and woodlands. North America, in comparison, shows a fragmented pattern of change notable only in the forests of the east and grasslands of the upper Midwest.
“When we looked at temperature and satellite vegetation data, we saw that year to year changes in growth and duration of the growing season of northern vegetation are tightly linked to year to year changes in temperature,” says Zhou. The area of vegetation has not extended, but the existing vegetation has increased in density.
Dramatic changes in the timing of both the appearance and fall of leaves are recorded in these two decades of satellite data. The authors report a growing season that is now almost 18 days longer, on average, in Eurasia, with spring arriving a week early and autumn delayed by 10 days. Myneni says scientists are debating whether or not the unprecedented warmth of the past 25 years has caused an unmitigated build up of heat-trapping gases in the atmosphere related to human activities. In North America, the growing season appears to have become 12 days longer.
The researchers used a temperature data set developed by the Global Historical Climate Network (HCN). Dr. James Hansen of NASA’s Goddard Institute for Space Studies in New York, who developed this data set, says, “The data were compiled from several thousand meteorological stations in the United States and around the world. The stations also include many rural sites where the data are collected by cooperative private observers.”
This research was funded by the NASA Earth Science Enterprise’s Pathfinder Data Sets and Associated Science Program.
For more information and images, visit http://cybele.bu.edu or http://www.gsfc.nasa.gov/topstory/20010904greenhouse.html on the World Wide Web.