NASA March 04, 2002 –
An “ozone hole”
could form over the North Pole after future major volcanic eruptions, according
to the cover story by a NASA scientist in tomorrow’s edition of the Proceedings
of the National Academy of Sciences.

Since the 1980s a seasonal ozone hole, characterized by severe loss of ozone,
has appeared over the continent of Antarctica. However, scientists have not yet
observed, on an annual basis, as severe a thinning of the protective ozone layer
in the atmosphere over the Arctic. The ozone layer shields life on Earth from
harmful ultraviolet radiation. A northern ozone hole could be significant since
more people live in Arctic regions than near the South Pole.

Azadeh Tabazadeh

“A ‘volcanic ozone hole’ is likely to occur over the Arctic within the next 30
years,” said Azadeh Tabazadeh, lead author of the paper and a scientist at
NASA’s Ames Research Center, Moffett Field, Calif. Her co-authors are: Katja
Drdla, also of Ames; Mark R. Schoeberl of NASA’s Goddard Space Flight Center,
Greenbelt, Md.; Patrick Hamill of San Jose State University, Calif.; and O.
Brian Toon from the University of Colorado, Boulder.

“If a period of high volcanic activity coincides with a series of cold Arctic
winters, then a springtime Arctic ozone hole may reappear for a number of
consecutive years, resembling the pattern seen in the Antarctic every spring
since the 1980s,” Tabazadeh said.

Unlike the Antarctic where it is cold every winter, the winter in the Arctic
stratosphere is highly variable,” Tabazadeh said. NASA satellite and airborne
observations show that significant Arctic ozone loss occurs only following very
cold winters, according to Tabazadeh.

Large volcanic eruptions pump sulfur compounds into the Earth’s atmosphere.
These compounds form sulfuric acid clouds similar to polar stratospheric clouds
made of nitric acid and water. The clouds of nitric acid and water form in the
upper atmosphere during very cold conditions and play a major part in the
destruction of ozone over Earth’s poles. Following eruptions, volcanic sulfuric
acid clouds would greatly add to the ozone-destroying power of polar
stratospheric clouds, researchers said.

“Volcanic aerosols also can cause ozone destruction at warmer temperatures than
polar stratospheric clouds, and this would expand the area of ozone destruction
over more populated areas,” Tabazadeh said. “Nearly one-third of the total ozone
depletion could be a result of volcanic aerosol effects at altitudes below about
17 kilometers (11.5 miles),” said the researchers.

“Volcanic emissions can spread worldwide,” said Schoeberl. “Our Mt. Pinatubo
computer simulation shows that the volcanic plume spread as far north as the
North Pole in the lowest part of the stratosphere within a few months after the

Between about 15 and 25 kilometers (9 to 16 miles) in altitude, volcanic Arctic
clouds could increase springtime ozone loss over the Arctic by as much as 70
percent, according to Drdla. “The combination of thick volcanic aerosols at
lower altitudes and natural polar stratospheric clouds at higher altitudes could
greatly increase the potential for ozone destruction over the North Pole in a
cold year,” Tabazadeh said.

Mt. Pinatubo

“Both the 1982 El Chichon and 1991 Mt. Pinatubo eruptions were sulfur-rich,
producing volcanic clouds that lasted a number of years in the stratosphere,”
Tabazadeh said. The Pinatubo eruption, as observed by NASA spacecraft, widely
expanded the area of ozone loss over the Arctic.

Mount Pinatubo Sulfur Dioxide Cloud (NASA TOMS)

Both of these eruptions did have an effect, however, over the South Pole,
expanding the area and the depth of the ozone hole over the Antarctic, according
to Tabazadeh. Computer simulations have shown that the early and rapid growth of
the Antarctic ozone hole in the early 1980s may have been influenced in part by
a number of large volcanic eruptions, she added.

“In 1993 the Arctic winter was not one of the coldest winters on record, and yet
the ozone loss was one of the greatest that we’ve seen,” Tabazadeh said. “This
was due to the sulfurous Pinatubo clouds facilitating the destruction of
additional ozone at lower altitudes where polar stratospheric clouds cannot

“Climate change combined with aftereffects of large volcanic eruptions will
contribute to more ozone loss over both poles,” Tabazadeh said. “This research
proves that ozone recovery is more complex than originally thought.”