261
See also: Global warming 202–203 ■ Environmental feedback loops 224–225
■ Pollution 230–235 ■ The Keeling Curve 240–241 ■ Environmental ethics 306–307THE HUMAN FACTOR
large dip. Farman decided it was
time to publish, and a paper written
by him and his colleagues Brian
Gardiner and Jon Shanklin appeared
in the journal Nature in 1985.Reaction and response
Most scientists greeted Farman’s
discovery with alarm: the potential
increase in UV radiation would make
skin cancers, cataracts, and sunburn
far more prevalent.
What could be done? One
reason for ozone depletion had been
identified in 1974 by Americanscientists Frank Rowland and
Mario Molina. They had concluded
that gases containing chlorine—
including the chlorofluorocarbons
(CFCs) used in aerosol sprays and
halogen refrigerants—were, in
the presence of UV light, reacting
with ozone in the stratosphere and
breaking down the gas. A few
countries, including the US, banned
the use of these products, but most
were yet to be convinced.
When ozone levels continued
to fall throughout the 1980s, opinion
gradually changed. Consequently,
in 1987, the Montreal Protocol for
a global ban was agreed. The ozone
layer is showing signs of recovery,
and it is hoped that by 2075,
stratospheric ozone will return
to 1975 levels. ■CFCs
Chlorofluorocarbons (CFCs)
are chemicals made up of
carbon, chlorine, and fluorine
atoms. They are non-toxic,
nonflammable, and extremely
stable. Their low reactivity
makes them very useful, but
is also the reason why they
are so destructive. They can
survive for over 100 years,
which gives them time to
diffuse into the stratosphere.
There, they are broken down
by the intense UV light to
release chlorine, which reacts
with ozone to form oxygen.
CFCs were first produced
in 1928, and were used as
coolants for refrigerators. They
were later used in a wide
range of aerosol products, for
example insect sprays, hair
conditioners, and spray paints.
The replacements for CFCs
were hydrochlorofluorocarbons
(HCFCs), which also deplete
the ozone layer, although to
a much lesser extent, and
hydrofluorocarbons (HFCs).
HCFCs will be phased out by- HFCs do not harm the
ozone layer at all—but they
are very powerful greenhouse
gases, and so in 2016 it was
agreed that, from 2019, they
too would be phased out.
A NASA image of the “ozone hole”
over Antarctica in 2014. The blue area
shows where there is least ozone. The
amount of ozone in Earth’s stratosphere
overall has stabilized since about 2000.Aerosol products such as insect
repellents were widely available
from the 1950s. The damaging
effects of the CFCs they contained
were not known until the 1970s.US_260-261_Hole_in_the_Ozone.indd 261 17/12/2018 14:34