The investigators analyzed satellite observations of planet-wide plant growth as well as patterns of temperature, rainfall, and cloud cover during the period between 1982 and 1999. They calculated the amount of carbon stored in vegetation, a measure known as net primary production (NPP), which is determined by subtracting the amount of carbon dioxide removed from the atmosphere by photosynthesis from that released into the atmosphere when plants respire.

NPP is important because it not only indicates how much carbon -- the building block of life on earth -- is available to use for food, fuel, or shelter, but it can also help to predict atmospheric levels of carbon dioxide, a measure related to global warming.

The researchers mapped changes in water availability, temperature, and sunlight during this period -- one in which earth experienced record-setting temperatures and three intense El Niño weather events. They were able to relate an increase in greening in the Amazon basin with thinning of the cloud cover and more sunlight, and vegetation growth in India with increased rainfall, a result of more dependable monsoons. Altogether, the period showed NPP growth of 6 percent -- making a 3 percent increase available for human consumption. During the same period, the earth’s population increased by about 35 percent, leaving a net loss in the amount of carbon available for human use.

This research was published in the June 6, 2003 issue of the journal, Science. Additional information is available on the Goddard Space Flight Center website and at http://cybele.bu.edu/greeningearth/ge.html.