tion near Halley Bay. During the mid-1980’s, the
cause of dramatic declines in ozone density over the
Antarctic was open to debate. Some scientists sus-
pected variability in the Sun’s radiational output,
and others suspected changes in atmospheric circu-
lation. A growing minority began to suspect CFCs. In
1987, a majority of the world’s national governments
signed the Montreal Protocol to eliminate CFCs.
Definite proof of the role of CFCs in ozone deple-
tion arrived shortly thereafter, as J. G. Anderson
and colleagues implicated the chemistry of chlorine
and explained a chain of chemical reactions (later
broadened to bromides as a bit player), the “smok-
ing gun” that explained why ozone depletion was so
sharp and limited to specific geographic areas at a
specific time of the year.
Impact Despite the Montreal Protocol, ozone de-
pletion over the Arctic and Antarctic accelerated dur-
ing the following years, exacerbated at least in part by
rising levels of greenhouse gases (carbon dioxide,
methane, and others) near the Earth’s surface. In an
act of atmospheric irony, warming near the surface
causes the ozone-bearing stratosphere to cool signifi-
cantly. The atmosphere’s existing cargo of CFCs (with
a lifetime of up to a century) consumes more ozone as
it becomes colder. An increasing level of carbon diox-
ide near the Earth’s surface acts as a blanket, trapping
heat that would have radiated through the strato-
sphere into space. The influence of global warming
near the surface on declining stratospheric tempera-
tures has continued, as loss of ozone over Antarctica
reached new records after 1989. Thus, until humanity
reduces its emissions of greenhouse gases, ozone de-
pletion will remain a problem long after most of CFC
production has ceased.
Subsequent Events By the year 2000, the ozone-
depleted area over Antarctica had grown, at its maxi-
mum extent, to an area two-thirds the size of Africa.
While the polar reaches of the Earth have been suf-
fering the most dramatic declines in ozone density,
ozone levels over most of the planet have declined
roughly 15 percent since the mid-1980’s. Late in Sep-
tember, 2006, the World Meteorological Organiza-
tion reported that the ozone hole’s size expanded to
10.6 million square miles (28 million square kilome-
ters), larger than the previous record extent during- This area of depleted ozone was larger than
the surface area of North America.
Further Reading
Aldhous, Peter. “Global Warming Could Be Bad
News for Arctic Ozone Layer.”Nature404 (April 6,
2000): 531. Examines the possibility that ozone
depletion could increase in the Arctic.
Austin, J., N. Butchart, and K. P. Shine. “Possibility of
an Arctic Ozone Hole in a Doubled-CO 2 Cli-
mate.”Nature414 (November 19, 2001): 221-225.
Addresses the relationship of global warming to
stratospheric ozone depletion.
Hartmann, Dennis L., et al. “Can Ozone Depletion
and Global Warming Interact to Produce Rapid
Climate Change?”Proceedings of the National Acad-
emy of Sciences of the United States of America97, no. 4
(February 15, 2000): 1412-1417. Covers the rela-
tionship of ozone depletion to global warming.
Rowland, F. Sherwood, and Mario Molina. “Strato-
spheric Sink for Chlorofluoromethanes: Chlo-
rine Atom-Catalyzed Destruction of Ozone.”Na-
ture249 (June 28, 1974): 810-812. The seminal
scientific article establishing, in theory, that CFCs
could deplete the ozone layer.
Bruce E. JohansenSee also Air pollution; Environmental movement;
Science and technology.742 Ozone hole The Eighties in America