260
I
n 1982, a team of scientists
working for the British Antarctic
Survey (BAS) discovered that
ozone levels above the Antarctic had
fallen dramatically. Ozone (O 3 , a
colorless gas in the stratosphere,
12–18 miles (20–30 km) above Earth’s
surface, forms the “ozone layer,” a
protective shield that absorbs most
of the Sun’s ultraviolet (UV) radiation.
Without it, more of the Sun's harmful
radiation would reach the surface.
Since the mid-1970s, there has
been a 4-percent decrease in the
amount of ozone in the stratosphere.
An even bigger decrease has been
seen above the poles, particularlyin spring. Over Antarctica, ozone
measurements have been down
by 70 percent compared with 1975.
Over the Arctic, levels have fallen
by nearly 30 percent. This effect
became known as “the ozone hole,”
although it is better described as
“the ozone depression,” since it is
a thinning of the ozone layer rather
than a complete hole.Antarctic discovery
British geophysicist Joe Farman
was one of the team who made
the discovery in 1982. BAS teams
had been collecting atmospheric
data at the Halley Research Station
in Antarctica since 1957. Their
work was poorly funded, and they
relied on dated instruments such as
the Dobson meter—a rudimentary
machine that worked properly only
when wrapped in a duvet.
When Farman first noticed the
drop in ozone levels, he found it
hard to believe, and thought there
must be a problem with his Dobson
meter. He ordered a new instrument
for the next year—and it recorded
an even bigger dip. The following
year, the dip was bigger again.
The year after, his team took their
measurements 620 miles (1,000 km)
from Halley. Again, there was aIN CONTEXT
KEY FIGURE
Joseph Farman (1930–2013)BEFORE
1974 American chemists
Frank “Sherry” Rowland and
Mario Molina suggest that
chlorofluorocarbons (CFCs)
destroy atmospheric ozone.1976 The US National
Academy of Sciences declares
that ozone depletion is a reality.AFTER
1987 The Montreal Protocol
on Substances that Deplete
the Ozone Layer, a global
treaty to phase out CFCs and
similar chemicals, is agreed.1989 Montreal’s worldwide
ban on the production of CFCs
comes into effect (ratified by
the EU and 196 states to date).2050 The year in which ozone
over the Antarctic is predicted
to return to pre-1980 levels;
however, other harmful
emissions may delay recovery.THE HOLE IN THE
OZONE LAYER IS A
KIND OF SKYWRITING
OZONE DEPLETION
Joe Farman [made]
one of the most important
geophysical discoveries of
the 20th century.
John Pyle and Neil Harris
Atmospheric scientists,
University of CambridgeUS_260-261_Hole_in_the_Ozone.indd 260 12/11/2018 17:34