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Percent change in satellite sensed greenness in the boreal summer months of May through September during the 1981-1991 time period

The Green, Green, Grass of Alaska!

Data from satellite observations indicate that in recent years spring has been coming as much as seven days earlier in the northern high latitudes, creating a longer growing season and significantly greening - increasing the amount of vegetation - in the area, according to research by Associate Professor of Geography Ranga Myneni.

The observations, taken between 1981 and 1991, suggest an early disappearance of snow in the region and show an increase in plant growth of about 10% in the latitudes between 45ºN and 70ºN (roughly from the latitude of Minneapolis/St. Paul, Minn. to the latitude of the northern coast of Alaska). They agree with observations of changes in the levels of carbon dioxide over the same period, which indicate an increase in photosynthetic activity. More recent observations (1992-98) indicate that this trend has continued.

The region observed in this study includes about 35.3 million square kilometers, or about 35% of the earth's area which is covered in vegetation during the month of August (the greenest month of the year). Such a significant increase in the amount of vegetation over such an immense area has enormous potential to influence the greenhouse effect and lower the concentration of carbon dioxide in the atmosphere.

The observations were made using the Advanced Very High Resolution Radiometers (AVHRR) on board the National Oceanic and Atmospheric Administration (NOAA) series of meteorological satellites (NOAA-7, -9 and -11).

Follow-up observations will be made by instruments that will fly on each of the EOS AM (TERRA), and PM satellites scheduled for launch in mid-1999. Instruments on these satellites will be able to view the entire surface of the Earth every two days. They include Myneni's Multi-angle Imaging SpectroRadiometer (MISR), designed to measure sunlight reflected by the Earth into space and the Moderate Resolution Imaging Spectrometer (MODIS) designed to measure light in the visible and infrared regions of the spectrum.

"Continuing to track this phenomenon is vital to understand how our environment is changing and what we need to do to adapt to changing conditions," says Myneni.

This research has been supported by the National Oceanic and Atmospheric Administration (NOAA) and the National Aeronautics and Space Administration (NASA).

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3 May 1999
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