Academic Reading — Test 74

Reading passage

For most of human history, the night sky was a familiar companion. The stars guided sailors across oceans, ordered the calendars of farmers, and inspired countless myths and works of art. Today, however, a growing proportion of the world's population has never seen the Milky Way as a continuous band of light. The cause is light pollution: the excessive or misdirected artificial illumination that brightens the night sky, washes out faint stars, and disrupts the natural rhythms of living things. Although it is among the most easily reversible forms of environmental degradation, it remains one of the least discussed. The most visible consequence of light pollution is its effect on astronomy. When artificial light scatters off dust and water droplets in the lower atmosphere, it produces a diffuse glow known as skyglow. This glow reduces the contrast between stars and the background sky, so that only the brightest objects remain visible to an observer in a city centre. Professional astronomers have responded by building major observatories in remote regions such as the deserts of Chile or the high volcanic peaks of Hawaii, where the air is dry and human settlement is sparse. Yet even these carefully chosen sites are not immune. As towns expand and new developments are constructed nearby, the surrounding skyglow gradually creeps upward, threatening the quality of observations that took decades and considerable expense to secure. For amateur stargazers without the resources to travel, the loss is more immediate: a hobby once enjoyed from a back garden now requires a long journey to find genuine darkness. The harm, however, extends well beyond the telescope. Many animals have evolved to depend on the regular alternation of light and darkness, and the introduction of artificial light at night can interfere with their behaviour in ways that are easy to overlook. Nocturnal insects are perhaps the most familiar example. Moths and other flying insects are drawn towards bright lamps, where they circle until they die of exhaustion or are taken by predators. Because insects sit at the base of many food chains, a decline in their numbers can ripple outward, reducing the food available to bats, birds and amphibians. Researchers increasingly regard artificial light as one contributor, alongside habitat loss and pesticides, to the worrying decline in insect populations recorded in recent decades. Other species are affected in subtler but equally serious ways. On many coastlines, newly hatched sea turtles instinctively crawl towards the brightest horizon, which under natural conditions is the open sea reflecting the faint light of the sky. Where beachfront hotels and roads glow brightly, the hatchlings turn inland instead, where they perish from dehydration or traffic. Migratory birds, many of which travel at night and navigate partly by the stars, can become disoriented by illuminated buildings and communication towers, sometimes colliding with them in large numbers. Even plants are not entirely exempt, since artificial light can alter the timing of seasonal events such as the shedding of leaves. Underlying many of these effects is a hormone called melatonin, which regulates sleep and other biological cycles in a wide range of organisms, including humans. Melatonin is produced chiefly in darkness, and exposure to light at night, particularly the blue-rich light emitted by many modern devices and street lamps, can suppress its release. In wildlife this disruption can affect reproduction, feeding and the ability to evade predators. In people, researchers continue to investigate possible links between chronic exposure to nocturnal light and disorders ranging from insomnia to more serious conditions, though firm conclusions remain elusive. What distinguishes light pollution from many other environmental problems is the relative simplicity of the remedies. Unlike greenhouse gases, which persist in the atmosphere for decades, light vanishes the moment a lamp is switched off. Shielding fixtures so that they direct light downwards rather than sideways or upwards prevents much of the waste that produces skyglow. Replacing harsh blue-white lighting with warmer tones reduces the impact on wildlife, and fitting timers or motion sensors ensures that light is provided only when it is genuinely needed. Several towns and even entire regions have adopted such measures and have established dark-sky reserves where lighting is strictly controlled. These examples suggest that, with modest changes in design and habit, communities can enjoy the benefits of artificial light while restoring some of the darkness that both science and nature require.