THE HUMAN FACTOR 253
celestial objects in the night sky.
In 1988, American astronomers Tim
Hunter and David Crawford founded
the International Dark-Sky
Association to protect the night
skies from light pollution. It was
the first organization of its kind.
Since then, studies have
examined the effects of light
pollution on plants and animals,
which rely on the cycles of light
and dark to govern life-sustaining
behaviors such as nourishment,
sleep, protection from predators,
and even reproduction. Such
research reveals a raft of ill-effects.
One study showed that trees in
Europe are budding more than a
week earlier than they were in the
1990s; this alters their period of
growth, and may mean that they fail
to drop their leaves and fruit and
enter the dormant phase in time to
avoid damage over the winter.Vicious circle
Light pollution also has a detrimental
effect on animals. Lights on tall
towers, for example, draw migrating
birds, causing them to crash into
the towers and into power lines.Artificial light can also damage
birds’ immune systems. Studies
have found that house sparrows
infected with the West Nile virus
carried the virus twice as long when
kept under dim light than when kept
in the dark—doubling the time in
which mosquitoes could bite them
and pass on the virus.
Ill-effects on animals can have
a knock-on effect on plants. When
moths, which are attracted to light,
are repeatedly drawn to artificial
sources, not only can they be killed
by exhaustion (because the light is
never extinguished), or by the heat
generated, but they also become
more vulnerable to predators, which
can spot them more easily.
The decline in moth numbers
has a knock-on effect on the plants
that they help pollinate, which then
affects seed yield. In some places,
seed yield has declined by as much
as 30 percent. Researchers who
studied a Swiss flower meadow
under street lights found that
nocturnal visits from pollinators
declined by two-thirds. ■The effect on turtles
Light pollution is a major
problem for nesting sea
turtles, which lay their eggs
on land because the embryos
breathe through the
permeable shells. Females
need dark, sandy beaches for
their nests, and will go
elsewhere if there are bright
lights from beach resorts,
street lights, or housing. If a
whole stretch of coastline is
illuminated, they may lay their
eggs in inferior habitats or
even deposit their eggs at sea,
where their offspring will die.
Such problems may be the
reason for the reduction in sea
turtle populations. Scientists
believe that hatchlings move
toward the brightest light. In
natural conditions, this will be
moonlight shining on the
ocean, but if there is artificial
lighting inland, the hatchlings
wander toward that and get
run over by traffic, eaten by
predators, or caught in fencing.
Solutions include getting
people and businesses to turn
off lights at night or use
“turtle-safe” lighting, which is
virtually invisible to turtles.Olive ridley sea turtle
hatchlings make their way toward
the sea at Boca del Cielo Turtle
Research Station, Mexico.See also: Environmental feedback loops 224–225 ■ Spring creep 274–279
■ Man and the Biosphere Programme 310–311Dark areas are being lost
in places where nocturnal
animals, insects, and plants
have adapted to darkness
over billions of years.
Franz HölkerThe solution is simple—
turn off unnecessary lights,
use only the amount of light
needed for the task at hand,
and shield all lighting
so it shines down
where it is needed.
Tim HunterUS_252-253_Light_Pollution.indd 253 17/12/2018 14:33