El Niño Events May Be Linked To Volcanic Eruptions, Study
November 19, 2003 --
new study by scientists at the University of Virginia and the National
Center for Atmospheric Research (NCAR) suggests
volcanic eruptions in the tropics may increase the probability
of an El Niño event occurring during the winter following
a volcano erupts in the tropics, its aerosol emissions spread
into the stratosphere across the northern and
reflecting some of the sun’s
heat back toward space and thereby cooling the Earth’s atmosphere. This
cooling alters the interaction between the oceans and atmosphere, possibly encouraging
a warming response in the Pacific Ocean as the massive body of water attempts
to restore an initial equilibrium.
results suggest that the atmospheric cooling from an eruption
may help nudge the climate system towards producing an El Niño
study co-author Michael Mann, an assistant professor of environmental sciences
at the University of Virginia.
study results will appear in the Nov. 20 issue of the journal
scientists had previously noted that during the 20th century,
events – the periodic warming of sea surface temperatures in the
equatorial Pacific -- tended to follow the eruption of volcanoes in the
tropics. But that
100-year period, the only time span for which reliable instrumental records
had been kept, was considered too short a duration to substantiate a link
the two phenomena. The connection was thought to be coincidental.
we turned to the paleoarchives for a longer history,” Mann
actually didn't expect the relationship to hold up in the long run.”
U.Va. and NCAR scientists instead found that, when looking back over
a 350-year period, as far back as paleorecords allow, there was
activity in the tropics may play a significant role in the occurrence
of El Niño
now have a long record showing that the relationship between
volcanic eruptions and an increased probability of El Niño
events continues to hold up over several centuries,” Mann
said. “It’s probably
not just a fluke.”
and his collaborators, U.Va. doctoral student Brad Adams, the
primary author, and NCAR atmospheric scientist Caspar M. Ammann,
used the paleoclimate
stored in ice cores, corals, and tree ring records to reconstruct
events and independent ice core volcanic dust evidence to reconstruct
volcanic activity back to the early 1700s.
paleoclimate records are called 'proxy records', because they
are not direct measurements
of current climate and ocean
of past conditions gleaned from the physical, biological, or
chemical records or, “signatures,” stored in natural
archives in the environment.
these records, the scientists were able to precisely identify
the years when eruptions occurred
and the years when
El Niño events occurred.
they counted, year by year, the separate events and brought them
together for comparison,
they found that there
was a nearly
an El Niño event will occur after a volcanic eruption
in the tropical zone, roughly double the normal probability.
wouldn’t call this a tight connection – it’s
not a one-to-one relationship,” Mann said, “but it
appears that the eruption of a tropical volcano nudges the climate
towards a more El Niño-like state.”
is a prominent altering factor on world climate, affecting weather
patterns for months and years, often causing drought
and severe weather in different parts of the world.
“We seek to understand how El Niño responds to changes in natural
factors such as volcanic activity in part, so we can potentially better understand
how El Niño might respond to more recent human influences on climate.” Mann
Adams added that the findings might help oceanographers
and atmospheric scientists to make better probabilistic
of El Niño activity.
is not a strictly predictive tool, but it may help in anticipating
the odds that an El Niño event might occur in a given period,” said
National Oceanographic and Atmospheric Administration and The
National Science Foundation sponsored the
National Science Foundation
is also the
sponsor for the National Center for Atmospheric
Research, which is headquartered in Boulder, Colo.
Fariss Samarrai, (434) 924-3778; Michael Mann
(434) 924-7770; Brad Adams, (703) 351-7256 and Caspar M. Ammann, (303) 497-1705