Depletion of Ozone
Ozone depletion is greatest at the South Pole.
It occurs mainly in late winter
and early spring (August-November) and peak depletion
usually occurs in early October,
when ozone is often completely destroyed in large areas.
This severe depletion creates the so-called “ozone hole” that
can be seen in images of Antarctic ozone,
made using satellite observations. In most years, the maximum area
of the hole is bigger than the
Antarctic
continent itself. Although ozone
losses are less radical in the Northern Hemisphere, significant
thinning
of
the ozone layer is also observed over the Arctic and even
over continental Europe.
Most of the ozone-depleting substances emitted by human activities
remain in the stratosphere for
decades,
meaning that ozone layer recovery
is a very slow, long process.
Ozone layer depletion causes increased UV radiation levels at the Earth's surface,
which is damaging to
human
health.
Negative effects include increases in certain types of skin cancers,
eye cataracts and immune
deficiency
disorders. UV radiation also affects terrestrial and aquatic ecosystems,
altering growth, food chains
and
biochemical cycles.
Aquatic life just below the water’s surface, the basis of the food chain
, is
particularly adversely affected by high UV levels.
UV rays also affect plant growth, reducing
agricultural
productivity.
Ozone layer depletion increases the amount of UVB that reaches
the Earth’s surface. Laboratory and
epidemiological studies demonstrate that UVB causes non-melanoma
skin cancer and plays a major role in
malignant melanoma development. In addition, UVB has been linked
to the development of cataracts, a
clouding
of the eye’s lens.
UVB radiation affects the physiological and developmental processes
of plants. Despite mechanisms to
reduce
or repair these effects
and an ability to adapt to increased levels of UVB, plant growth can be
directly
affected by UVB radiation.
Indirect changes caused by UVB (such as changes in plant form,
how nutrients are distributed within
the
plant, timing of developmental phases
and secondary metabolism) may be equally or sometimes more
important
than damaging effects of UVB. These changes can have important
implications for plant competitive
balance,
herbivory, plant diseases, and biogeochemical cycles.
Phytoplankton form the foundation of aquatic food webs.
Phytoplankton productivity is limited to the
euphotic
zone, the upper layer of the water column in which there
is sufficient sunlight to support net
productivity.
Exposure to solar UVB radiation has been shown to affect
both orientation and motility in phytoplankton,
resulting in reduced survival rates for these organisms.
Scientists have demonstrated a direct reduction
in
phytoplankton production due
to ozone depletion-related increases in UVB.
UVB radiation has been found to cause damage
to early developmental stages of fish, shrimp, crab,
amphibians, and other marine animals. The most severe effects
are decreased reproductive capacity and
impaired larval development. Small increases in UVB exposure could
result in population reductions for
small
marine organisms with implications for the whole marine food chain
.
Synthetic polymers, naturally occurring biopolymers,
as well as some other materials of commercial
interest
are adversely affected by UVB radiation.
Today's materials are somewhat protected from UVB by special
additives. Yet, increases in UVB levels will accelerate their breakdown,
limiting the length of time for
which they are useful outdoors.