by DK
In recent years, accelerating and decelerating warming trends have brought the idea of feedback loops to the fore in climate change science. In 1988, the climate scientist James Hansen spoke at a US congressional hearing of the rises in global temperature caused by human activity. He has since voiced the belief that the continued burning of fossil fuels could set in motion a series of calamitous positive feedbacks on Earth’s climate, leading to the “runaway greenhouse” he describes in his 2009 book Storms of My Grandchildren.
One warming feedback loop is created by the melting of polar ice caps, as newly exposed land and water absorb the heat that the ice once reflected back into the atmosphere. The melting of Siberian permafrost is another warming loop. As temperature rises melt the permafrost, huge amounts of methane, a greenhouse gas, could be released into the atmosphere, accelerating global warming.
See also: Predator–prey equations • Competitive exclusion principle • Global warming • Halting climate change
INTRODUCTION
Raw sewage produced by millions of Londoners once poured into the Thames River for decades, until the stench of the effluent became so bad that in 1858 action was demanded. When a new system of sewers, pumping stations, and treatment works revolutionized the city’s sanitation, deaths and illness from cholera and other bacterial infections fell dramatically, and the river became much cleaner.
Human activity has always altered the environment, but its impact increased dramatically in the mid-18th century with the Industrial Revolution that began in Britain, and spread to Europe, North America, and beyond. The negative effects can be broadly divided into pollution, and destruction of resources and habitats.
Scottish-American environmentalist John Muir was one of the first to identify habitat degradation and destruction as problems, and in 1890 he won protection for the Yosemite Valley in California. However, despite a steady increase in protected natural environments, in the 20th century, the destructive pressures of human development have grown ever more powerful.
Trees and climate change
Forest has been especially hard-hit, mainly due to the dual demands of lumber required for construction and fuel, and land cleared for agriculture and development. An estimated 54,000 sq miles (140,000 sq km) of tropical rain forest—which contains the greatest biodiversity—is cleared each year. Scientists will never know how many forest-dwelling species died out before they were “discovered.”
Deforestation also contributes to global climate change. As trees photosynthesize, they absorb carbon dioxide and release oxygen. However, less forest means that more CO2 stays in the atmosphere, fueling the greenhouse effect and global warming.
Carbon and other greenhouse gases are emitted from cars and factories burning fossil fuels. Since 1958, American scientist Charles Keeling’s measurements of atmospheric CO2 have shown that CO2 emissions are increasing at an ever-faster rate. While a minority of scientists maintain that human activity is not responsible, climate change has warmed the continents. The consequences, including trees coming into leaf and flowers blooming earlier in spring, may benefit some organisms but could prove disastrous for others.
Toxic controls
The introduction of pesticides, such as DDT, to increase crop harvests proved to be an environmental disaster: they eradicated useful invertebrates as well as harmful ones; they caused cancers in humans; and rendered birds of prey infertile. Rachel Carson’s 1962 book Silent Spring highlighted many of these issues, and caused a partial rethink of pesticide use. The work of several other ecologists has resulted in legislative controls to mitigate the environmental impact.
When Gene Likens and his team investigated why previously fish-rich lakes had died, they found that the culprit was acid rain, caused by emissions of sulfur dioxide and nitrogen oxide from industrial chimneys. As a result, legislation to control the emissions was passed in the US and Europe. After US chemists Frank Rowland and Mario Molina showed that chlorofluorocarbons (CFCs) destroy atmospheric ozone, the use of CFCs was banned worldwide in 1989.
Light pollution, which affects beach-nesting turtles, bats, and migrating birds, has proved harder to control. The International Dark-Sky Association is at the forefront of campaigns for environmentally responsible lighting.
Diminished resources
Garrett Hardin, an American ecologist, warned of the dangers of overpopulation in 1968, when the global population was 3.6 billion. By 2018, it had swollen to 7.6 billion, and although the growth rate has slowed considerably, the ever-increasing consumption of natural resources has led to depleted stocks of wood, fossil fuels, minerals, and even fish. The collapse of the once bountiful cod fishery off Newfoundland in 1992 highlighted the vulnerability of our food chain to overfishing and led the Canadian government to impose an indefinite moratorium on fishing on the Grand Banks.
Clean water is one of the most fundamental requirements for society but almost 1 billion people do not have access to it. A lethal combination of climate change and population growth in some developing regions threatens to increase this number.
IN CONTEXT
KEY FIGURE
Emma Johnston (1973–)
BEFORE
1272 King Edward I of England bans the burning of sea coal in London because of the smoke it produces.
19th century Coal-burning during Britain’s Industrial Revolution stunts children’s growth and raises death rates from respiratory diseases.
AFTER
1956 The Clean Air Act is introduced in the UK, bringing the thick smogs that plagued its major cities to an end.
1963 The Clean Air Act is passed in the US.
1972 The Clean Water Act is fully ratified in the US.
1984 Toxic gas leaks from the Union Carbide India factory in Bhopal kill thousands and injure many more.
Pollution comes in many forms, ranging from toxins in the air to trash at the bottom of the sea. Any substances or forms of energy that spoil the quality of the atmosphere, oceans, water, or soil are pollutants. They may be chemicals or biological contaminants (including human waste), products (such as plastics), or noise, light, or heat. The effects of pollution on life of all kinds can be far-reaching, spreading thousands of miles beyond its original source. Pollution can spread through the food chain and be carried through air and water, affecting all life. Contaminants such as plastics can facilitate the invasion of nonindigenous species, as discovered by Australian marine biologist Emma Johnston. There is also a direct effect on human health: it is estimated that exposure to polluted air, water, and soil caused 9 million premature deaths—one in six of all deaths—in 2015.
Polluted air and water cause the deaths of millions of people every year. This illustration describes the specific damage caused to different organs of the human body.
Pollution through the ages
Human-made pollution has a long history. The presence of soot on the walls of caves, dating back thousands of years, indicates that early humans generated air pollution from their fires. Analysis of 2,500-year-old ice cores in Greenland has shown evidence of air pollution from copper smelting thousands of miles away, in the center of the Roman Empire. However, such impacts were on a small scale. With the start of the Industrial Revolution in Europe, air and water pollution became serious. Factory chimneys pumped smoke out into the air; toxic chemicals poured into rivers. Cities expanded quickly and had no sanitation. The Thames River, in London, was both the source of water for domestic use and the outlet for untreated human sewage. Disease spread, river fish were wiped out, and the smell was sometimes unbearable. Other urban centers fared little better: similarly unsanitary conditions were recorded in Berlin in 1870, for example.
In the United States, the first two cities to enact laws to ensure clean air were Chicago and Cincinnati, in 1881. By that time, the manure from 3 million horses pulling wagons in North American cities was seeping into water supplies and producing plagues of disease-causing flies. As horses were gradually replaced by the internal combust
ion engine, smog from cars and trucks became a major issue. London’s Great Smog of 1952, described as a “pea-souper” for the color of the filthy air, killed more than 4,000 people.
“Air pollution control systems still lag behind economic development.”
Bob O’Keefe
The “Great Stink”
This cartoon, published in Punch magazine in July 1858, was entitled “The Silent Highwayman.” People at the time attributed the spread of cholera to the bad river smells.
By the early 19th century, London’s Thames was the most polluted river in the world. Industrial pollution and human effluent emptied into it from thousands of drains. People complained, but the government did nothing. In 1855, the scientist Michael Faraday lambasted politicians for their inaction, to no avail. However, they got the message three years later, when a hot summer contributed to the “Great Stink” of 1858. The Houses of Parliament, being adjacent to the Thames, were badly affected, and legislation was suddenly enacted in a mere 18 days.
Civil engineer Joseph Bazalgette was commissioned to design a new sewage system. It was based on six interceptor sewers, 100 miles (160 km) long, which flowed to new treatment works. Most of London was connected to it within a decade. Much of the sewage system is still in operation today, more than 150 years later.
Air pollution
The result of harmful substances being released into the atmosphere, such as gases or small particles called aerosols, air pollution can have natural sources, such as volcanoes or wildfires, but is mainly caused by human activity. The main air pollutants are emissions from fossil-fuel-burning power stations, factories, motor vehicles, the burning of wood and dung for heat and cooking fuel, and methane from cattle, landfill sites, and fertilized fields. Poor air quality damages human health and crops, and some fossil-fuel emissions cause acid rain, which has killed forests and fish in thousands of lakes.
The World Health Organization (WHO) estimates that nine out of ten people worldwide are breathing polluted air, causing widespread illness and allergies. Furthermore, some aerosols, depending on the composition and color of the particles, block the amount of solar radiation reaching Earth’s surface, thus having a cooling effect on the planet. Efforts to reduce air pollution can therefore make the effects of global warming worse.
Of the world’s 20 worst cities for air pollution, 14 are in India. In Delhi, thick smog in November 2017 reduced the air quality to the equivalent of smoking 50 cigarettes a day.
Rivers, lakes, and seas
Surface water, groundwater, and the oceans become contaminated by toxic chemicals from industry, from chemical runoff from farmland, from general trash such as plastics, and from human waste.
Some rivers and lakes are so polluted that they can support no life at all, deprive communities of freshwater and food, and carry a risk of waterborne diseases, such as polio, cholera, dysentery, and typhoid. The WHO estimates that 2 billion people worldwide are drinking water contaminated with human waste, resulting in the deaths of 500,000 people a year.
In the oceans, the most acutely destructive pollution has resulted from disasters involving oil tankers and oil terminals. When the Exxon Valdez supertanker broke up on rocks off the coast of Alaska in 1989, 11 million gallons (50 million liters) of crude oil were released into the North Pacific. The oil smothered or poisoned an estimated 250,000 seabirds, 250 Bald Eagles, 2,800 sea otters, 300 harbor seals, and 22 killer whales. Billions of salmon and herring eggs also died. Further catastrophic damage followed in 1991, during the Iraq War, when Iraqi forces opened the valves of an offshore oil terminal and released at least 380 million gallons (1,700 million liters) into the Persian Gulf. The long-term effects of such disasters are still unfolding and have yet to be fully understood.
Much of our nondegradable products ends up in the oceans. Since the 1950s, around 8.3 billion tons of plastic has been produced, of which only a fifth has been recycled or incinerated. Each year, a staggering 8 million tons of plastic reaches the oceans, and is responsible for the deaths of huge numbers of marine animals.
Orcas may become extinct as a result of PCB (polychlorinated biphenyl) pollutants. The compound becomes more concentrated higher in the food chain, and orcas are apex predators.
“Pollution is one of the biggest problems we are facing globally, with horrible future costs to society.”
Maria Neira
Intangible pollutants
Pollution in the form of energy, be it light, noise, or heat, can be just as intrusive as physical waste or chemical emissions. Light pollution from buildings, streetlights, vehicles, and advertising billboards was first described as a problem in New York in the 1920s. It can cause problems for nocturnal wildlife, for example, because predator–prey relations are interrupted. Excessive noise can be highly disturbing in cities, on flight paths, and near factories and roads. But it also affects wildlife in subtler ways. There is evidence that some birds now sing at night because their song can be heard more clearly than during the day.
Waste heat, too, can be damaging. When water from rivers or the sea is used as a coolant in factories or power stations, the hot water that is returned to the source is a form of thermal pollution. It can kill fish and alter the composition of the food chain, reducing biodiversity.
Nuclear energy is sometimes viewed as “cleaner” than fossil-fuel energy, because it does not produce greenhouse gases, but it does result in waste that remains radioactive for thousands or millions of years. The industry also bears the inherent risk of accidental damage. An explosion at the Chernobyl nuclear power plant in Ukraine in 1986 killed dozens of people and spread radiation across Western Europe. The slowly dwindling effects of contamination on the ecosystem and human health are predicted to last a century.
“In 2015, pollution caused three times as many deaths as AIDS, tuberculosis, and malaria combined.”
Philip Landrigan
Mitigation measures
Tackling the problem of pollution is a huge challenge, and involves both cleaning up existing pollution and making changes to reduce the rate at which we add to it. Key aspects of this include replacing fossil fuels with sustainable energy, more recycling and reuse, and the replacement of nondegradables with degradable materials. This will take time and, ultimately, demands a fundamental shift in our culture of consumption.
EMMA JOHNSTON
Born in 1973, Australian marine biologist Emma Johnston was interested in the oceans from an early age. She gained her Ph.D. in marine biology in 2002 and, in 2017, became the Dean of Science at the University of New South Wales (UNSW), and Head of the UNSW’s Applied Marine and Estuarine Ecology Lab, which investigates human impacts on marine ecosystems.
Johnston discovered how nonnative species can invade waterways in coastal areas by adhering to rafts of plastic pollution floating on the oceans. She has also studied marine communities in the Antarctic, developed new biomonitoring techniques, and advised agencies on the management of estuarine biodiversity.
Key works
2009 “Contaminants reduce the richness and evenness of marine communities,” Environmental Pollution
2017 “Building ‘blue’: an eco-engineering framework for foreshore developments,” Journal of Environmental Management
See also: The legacy of pesticides • Acid rain • Light pollution • A plastic wasteland • The water crisis • Waste disposal
IN CONTEXT
KEY FIGURE
John Muir (1838–1914)
BEFORE
1872 Yellowstone, in the states of Wyoming, Montana, and Idaho, is declared a national park—the first in the world.
AFTER
1948 The International Union for Conservation of Nature (IUCN), a partnership of governments and civil society organizations, is founded.
1961 The World Wide Fund for Nature (WWF), initially known as the World Wildlife Fund, is formed, to protect endangered species and habitats.
1971 The Man and the Biosphere Programme (MAB) is founded by
the United Nations, to promote sustainable development. It has a global network of Biosphere Reserves.
The origin of the movement to conserve natural habitats is usually credited to the Scottish–American naturalist John Muir, described as the “father of the national parks.” He was one of the first to realize that in order to survive, wild places needed legal protection. Of the many types of natural habitat on Earth, some are more fragile than others, but each faces different threats, whether anthropogenic (human-made) or from natural causes, or both, and many are critically endangered.
Habitats have, of course, always been affected by destructive natural events. Every year, lightning strikes trigger large grassland and forest fires. Hurricanes and rivers in flood can wreak havoc. Storm surges may produce inundations of the sea, turning freshwater wetlands saline. About 65 million years ago, the Chicxulub meteor impact in Mexico produced a dust cloud so great that it stopped sunlight from reaching Earth’s surface. Plants struggled to photosynthesize, and many animals, including the dinosaurs, became extinct.
Nor is human influence an exclusively recent issue. Throughout history, people have modified their environment. Deforestation, for example, is not a new problem. In Europe, the clearance of forests for agriculture and construction began thousands of years ago, and a similar pattern followed in North America.