by DK
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.
A map of light pollution across North America (white and red indicate where it is highest, black where it is lowest) explains why 99 percent of Americans cannot see the Milky Way.
“Dark areas are being lost in places where nocturnal animals, insects, and plants have adapted to darkness over billions of years.”
Franz Hölker
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 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 Hunter
The effect on turtles
Olive ridley sea turtle hatchlings make their way toward the sea at Boca del Cielo Turtle Research Station, Mexico.
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.
See also: Environmental feedback loops • Spring creep • Man and the Biosphere Programme
IN CONTEXT
KEY FIGURE
Chico Mendes (1944–88)
BEFORE
1100–1500 Temperate forest is cleared across large parts of western and central Europe.
1600–1900 Forests are cut down in North America to make room for agriculture.
Late 1970s Tropical rain forest clearance, mostly for ranching, accelerates dramatically.
AFTER
2008 The UN launches its Reducing Emissions from Deforestation and Degradation (REDD) incentive program.
2010 The US converts $21 m (£16 m) of Brazil’s debt into a fund that will protect Brazil’s coastal rain forest.
2015 The UN Paris Agreement sets targets for planting trees to offset the threat of climate change and global warming.
Deforestation is the removal of forest or woodland for conversion to nonforest use. This can be conversion to agricultural land, including cattle ranches, or development for housing, industry, or transportation. Forest may be degraded without being destroyed completely, when valuable mature trees, such as teak, are selectively logged or some trees are cut down to create a road. This can have a disproportionate negative effect on the biodiversity of the forest, even though most trees are left standing. Another form of deforestation is the clearance of primary forest and its replacement with monoculture plantations, such as palm oil, as has happened extensively in Indonesia.
Deforestation can impact all kinds of forest habitat, but tropical rain forest—tropical moist broadleaf forest that grows between the Tropic of Cancer and the Tropic of Capricorn—is the most severely affected. Concern for the rain forest was first raised in the 1970s when activist Chico Mendes—who went on to become a founding member of Brazil’s National Council of Rubber Tappers—called on the Brazilian government to establish forest reserves, from which local people could extract natural products, such as nuts, fruits, and fibers, sustainably. Mendes’s campaign, which eventually cost him his life, highlighted the ecological damage wreaked by forest clearance.
“By felling trees … men bring upon future generations two calamities at once: want of fuel and scarcity of water.”
Alexander von Humboldt
19th-century German explorer
Polluting smoke swirls up as rain forest burns to make way for agriculture in Brazil. It is estimated that Brazil clears 2.7 million acres (1.1 million hectares) of rain forest a year.
Human need
The human race has used trees from its earliest days. In Neolithic times, they were cut down for fuel and to construct shelters and fencing. Five-thousand-year-old stone axes for chopping wood have been found, as well as ax factories from the same era in Europe and North America. During the Middle Ages, however, as human populations expanded rapidly in western Europe between 1100 and 1500, extensive deforestation took place. Forests were cleared to make way for agriculture, and wood was used to build homes and boats, and to make bows, tools, and other implements.
Trees were cut down on an industrial scale in central Europe and England to produce charcoal, which became an important fuel (until replaced by coal) because it burns at higher temperatures than wood. An early example of sustainable production was practiced in England, where many woods were managed as coppices whose trees were partially cut back and then allowed to regrow to create a cyclical supply of charcoal. Even so, by the 17th century England had to import wood for shipbuilding from the Baltic nations and New England in the US.
Primeval forest clearance accelerated globally between 1850 and 1920, with the biggest losses in North America, the Russian empire, and South Asia. In the 20th century, the focus shifted to the tropics, especially to tropical rain forest, half of which has been destroyed since 1947, with the proportion of the land that it covers having fallen from 14 percent to 6 percent.
It is estimated that an area equivalent to 27 soccer fields is lost from forests globally each minute. Some regions have been hit harder than others. In the Philippines, for instance, 93 percent of tropical broadleaf forest has been removed; 92 percent of Atlantic forest in Brazil has gone; 92 percent of temperate coniferous forest in southwest China has disappeared; and 90 percent of dry broadleaf forest in California has been cleared.
“We are unable to remain silent in the face of so much injustice.”
Chico Mendes
Effects on biodiversity
Recent estimates suggest that almost half of all forest clearance is carried out by subsistence farmers, and a third by commercial interests. Urban development, logging for the best-quality lumber, mining and quarrying, and trees cut for firewood account for any remaining deforestation. In every case, the environment suffers. Biodiversity is particularly impacted, b
ecause only a small number of mammal, bird, and invertebrate species can live on grassland or a palm oil plantation, and even fewer in industrial or urban settings. Human conflicts also blight forest, the worst example being the Agent Orange chemical used to defoliate trees during the Vietnam War.
CHICO MENDES
Born in 1944, the son of one of the 50,000-strong “Rubber Army” who tapped rubber for use in the Allied war effort in World War II, Mendes started work as a rubber tapper at the age of nine. Influenced by priests from the progressive Liberation Theology movement, he helped found a branch of the Workers’ Party and became leader of the Rubber Tappers’ Union.
As large areas of Brazil’s rain forest were cleared to make way for cattle ranches, Mendes publicized the tappers’ fight to save the forest. He went to Washington, D.C., to persuade Congress and the World Bank that cattle-ranching projects should not be funded. Instead, hr proposed that forest areas be protected as “extractive reserves”—public land managed by local communities with the right to harvest forest products sustainably. Cattle ranchers saw his movement as a threat, and one, Darcy Alves, shot him dead in 1988. After his death, the first of many such reserves was established, covering 2.5 million acres (1 million hectares) of forest around Xapuri.
The rain forest
Destruction of the rain forest poses a severe threat to global biodiversity because it has been estimated that between half and two-thirds of the world’s plants and animals live in this environment. Between 1.5 million and 1.8 million species—mostly insects, followed by plants and vertebrates—have already been identified in rain forests, and many others have yet to be discovered and described. In Borneo, Indonesia, for example, an area of just 0.2 sq mile (0.5 sq km) may contain more species of tree than the combined landmass of Europe and North America. Such biodiversity is vitally important to humans—not least because most new medicines are derived from plants, and so the eradication of the rain forest’s rich store destroys potential cures for disease.
Rain forests, together with all other trees and woodland, also act like a sponge for rainfall. Tree roots drink up moisture and limit surface runoff. When forest is cut or burned, the soil is leached of many of its nutrients. If it covers a slope, the soil will wash away, leaving the land unfit for growing any kind of plants. Deep gullies may undermine trees that have not been cut, bringing them down. After heavy rains, catastrophic mudslides, which happen with increasing frequency, sweep down the slope, destroying everything in their path—including human settlements. In May 2014, for example, heavy rainfall on the deforested slopes of the Caribbean island of Hispaniola caused mudslides and floods that killed more than 2,000 people. Conversely, in extended periods of dry weather, exposed soil dries out faster than tree-covered areas, making it more prone to wind erosion.
Replacing trees with human settlements destabilizes the soil on slopes, and mudslides, such as this catastrophic event in Sierra Leone in 2017, are more likely to occur.
“I became an ecologist long before I had ever heard the word.”
Chico Mendes
Fueling global warming
Burning wood or forests adds carbon dioxide (CO2) to the atmosphere. By contrast, living plants of all kinds reduce CO2, as they absorb carbon, taking up the greenhouse gas to perform photosynthesis, thus countering the damaging impact of human activities. Globally, forests suck up 2.65 billion tons (2.4 billion tonnes) of CO2 every year. Environmentalists and climatologists worry that removing large tracts of tropical forest could be disastrous.
The depleting rain forest cover in the Amazon Basin is a global concern. The land is now being stripped of trees at a rate of 3,000 sq miles (8,000 sq km) annually.
Reforesting Earth
Currently, about 31 percent of Earth’s land surface is covered by forests, but that figure is rapidly decreasing in some parts of the world. However, there are regions, including Europe, where forest areas are gradually expanding. Measures to restrict deforestation include payments to communities for conserving forest, and the creation of extractive reserves, where local people can harvest products sustainably.
Globally, alternative sources of fuel need to be found, along with new ways to develop less land-hungry forms of agriculture. A few nations are taking the lead in reforestation programs. For example, a project in which people from 500 villages have planted 150 million mangrove trees on the coast of Senegal will restore mangrove forests to boost fishing and shield rice paddies from the influx of salt water. The Chinese aimed to plant 16.3 million acres (6.6 million hectares) in 2018, equal to the area of Ireland; in 2000, the proportion of China covered by forest had fallen to 19 percent, but the target is to increase this to 23 percent by 2020 and 26 percent in 2035.
The first African woman to win a Nobel Peace Prize (2004), Wangari Maathai initiated a community-based tree planting program to reverse erosion and desertification in Kenya.
Reforesting the Amazon
About 17 percent of rain forest in the Amazon Basin has been lost since the mid-1970s. At the United Nations Paris Climate Summit in 2015, Brazil pledged to restore nearly 30 million acres (12 million hectares) by the year 2030. In 2017, Conservation International, in partnership with the Brazilian government, launched the area’s biggest reforestation program to date, under which Amazonas state will gain 73 million trees through seeding and planting.
Local communities are being enrolled to implement the program, using a technique called muvuca. This involves spreading the seeds of more than 200 native forest species over every square yard of land. Less labor-intensive than traditional tree-planting, the method can reforest land quickly, delivering around 6,000 plants per acre. In addition to the seeding program some planting will enrich secondary forest and return pasture land to forest.
See also: Biodiversity and ecosystem function • Climate and vegetation • Global warming • A holistic view of Earth
IN 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.
In 1982, a team of scientists working for the British Antarctic Survey (BAS) discovered that ozone levels above the Antarctic had fallen dramatically. Ozone (O3, 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, particularly in 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.
“Joe Farman [made] one of the most important geophysical discoveries of the 20th century.”
John Pyle and Neil Harris
Atmospheric scientists, University of Cambridge
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 re
lied 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 a 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.
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.
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 American scientists 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.