Brian Dunbar
Headquarters, Washington, D.C.                                                                             
July 19, 1991
(Phone:  202/453-1547)

John J. Loughlin II
Goddard Space Flight Center, Greenbelt, Md.
(Phone:  301/286-5565)


RELEASE:  91-114

NASA GLOBAL CHANGE STUDY RAISES NEW QUESTIONS


    A NASA study, released today, indicates that the Sahara 
Desert, the world's largest desert, has undergone a variety of 
fluctuations in size during the past 11 years.

    Since 1980, scientists at NASA's Goddard Space Flight Center, 
Greenbelt, Md., have been studying data from a variety of Earth 
observing satellites in an effort to provide insight on global 
climatic change.  To accomplish this, scientists have engaged in 
a wide range of complementary studies of satellite data.  One 
study focused on the size of the Sahara Desert in Africa using 
meterological satellite data.

    "The object of this study was to look at the size of the 
Sahara Desert to see if it is increasing in size," according to 
Dr. Compton J. Tucker, Goddard Earth scientist. Scientists 
believe that changes in global desert area would mean that the 
Earth is undergoing a climate change on a global scale.

    "Our data indicate the Sahara has expanded at times and 
contracted at other times since 1980," he said.  "We can't say 
for sure, based on this data, whether or not the climate is 
changing. However, data such as these will provide a baseline to 
compare future data against to hopefully answer this question."



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     The data indicate that the southern boundary of the desert 
had expanded to the south about 80 miles from 1980 to 1990, but 
that there were rather dramatic movements both northward and 
southward within this time period.  The northern boundary 
includes the Atlas Mountains and the Mediterranean Sea, and, 
therefore, is not subject to large shifts.  After a big movement 
towards the south from 1981 to 1984, the Sahara retreated 
northward about 88 miles during the period from 1985 to 1986, 
then, migrated 34 miles back south in 1987.  The southern 
boundary then retreated northward 62 miles in 1988 before 
expanding to the south 46 miles in 1989 and 1990 where it lies 
today.

    "The fluctuations are determined by the amount and 
distribution of the rainfall in the area," Tucker said.  "That 
controls the amount of vegetation we see from space."  Those data 
were obtained from four National Oceanic and Atmospheric 
Administration satellites, NOAA-6, 7, 9 and 10, launched by NASA.  
The satellite data are derived by measuring the red and infrared 
light energy reflected back into space from the Earth's surface.  
"It is impossible to study large-scale climatic phenomena without 
Earth-orbiting satellites," Tucker said.

    Dr. Tucker collaborated with Wilber Newcomb, of Goddard, and 
Harold Dregne, of Texas Tech University, Lubbock, Texas, on the 
Sahara study.

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