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Contact: Jim Doyle, JPL                        DECEMBER 10, 1991

     The transition from a warm climate to the Little Ice Age in
the early 14th Century, marked by heavy precipitation, may have
set the stage for a series of plagues, including the Black Death
(1346-51), a Jet Propulsion Laboratory scientist said.

     In a presentation before a session of the American 
Geophysical Union's Fall Meeting in San Francisco Dec. 10, Kevin
Pang said an antique Chinese encyclopedia of historical events 
along with other physical records indicate that pestilence
followed the radical climatic changes.

     The increased rainfall year after year, beginning in 1315
"very likely raised biomass production in the Eurasian steppes
and deserts, and that in turn fed a rodent population explosion,"
he said.

     The cool, humid conditions also favor the breeding and
survival of fleas. The climatic changes coupled with some unique
historical events paved the way for a series of flea- and rat-
borne epidemics that killed a third of the population of Europe.

     A century of very destructive wars started by Genghis Khan
laid waste to much of the farmland in northern China, central and
western Asia and eastern Europe. Vast areas from the Pacific to
the Black Sea were fallow and depopulated; herding and huntingwere 
reduced.

     With less competition for food from herds and fewer hunters,
wild rodents spread from Eurasian plague reservoirs, infected
domestic rats. Commerce and mass migrations helped spread the
plague throughout the medieval world.

     The Gujin Tushu Jicheng, a 1726 encyclopedia of historical
events lists 25 great epidemics in the period 1344-80. Although
it gives no clinical details, Pang said he concluded the
epidemics were bubonic plagues since their geographical and
seasonal patterns were identical to the modern pandemic of 1894-
1950 in China.

     "Simultaneous outbreaks in the east, middle east and west
required profound ecological changes over Eurasia," he said.

     Medieval physicians did not know that bubonic plague is
caused by germs and spread by fleas and rodents, but noted in
1348-49 that "for a long time the seasons have not been marked by
their proper weather ... summer has been much less warm," and "an
abundance of rain has been present to a high degree for three
years."

     The climatic changes were confirmed by analyses of grape
harvest dates, Alpine tree rings and weather diaries. In all but
two years between 1343 and 1351, the Yellow River breached its
dikes and followed a new course to the sea.

     Pang said the records are consistent with 14th Century
western U.S. tree ring width measurements. Chinese texts also
recorded greatly increased dim and red suns in the 1330s and 
1340s, suggesting volcanic clouds contributed to the cool and wet
climate.

     Large volcanic acid peaks found in Greenland and Antarctic
ice cores for the period confirm it, he said.

     The first known bubonic plague pandemic began in the year
541 A.D., known as the Justinian plague, it started in the port
cities of Egypt, spread around the Mediterranean and decimated
the Eastern Roman Empire.

     The Black Death (1346-51) and subsequent plagues later in
that century killed tens of millions of Europeans and Asians. The
third plague pandemic began in China in 1894, spread to India,
and lasted for some 50 years, killing about three million Indians
and Chinese.

     Many public health experts predict that climatic changes
associated with global warming and ozone depletion could help
spread parasitic, especially insect-borne, diseases to regions
now unaffected, although the exact locations and degrees of
severity are difficult to pin down.
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