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.

“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,
located in California’s Silicon Valley. 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, said Drdla.

“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 eruption.”

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.

“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.

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 form.”

“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

More information is available at: