Chapter 49: People and the Biosphere

Section 1: Human Population

Human Population

• When humans formed permanent settlements, they began a long history of profoundly affecting the environment

• They made changes to the environment that were not easily undone

• Because people did not really understand how the natural environments on Earth functioned, they could not assess the effects of their activities on the environment

• For a long time, the human population was unaware that it was harming the world around it

Human Population

• Over time, the human population has increased dramatically – as has our knowledge of the Earth’s fragile environments

• Today we are more aware of how our actions affect our world

• But at the same time, we are also more capable of permanently damaging not just particular places on Earth but the entire biosphere itself

Population Growth

• Many environmental problems seem large and urgent today because of the rapid increase in human population

• The huge numbers of humans on Earth are making enormous demands on the planet

• A population grows when the birthrate is greater then the deathrate– Both of these must be taken into consideration

when trying to understand the growth of the human population

Birthrate

• Vary dramatically from one country to another• In the US and much of Europe, the birthrate

decreased during the 1970s• In the 1980s, American birthrates rose slightly• If current birthrates are maintained, our

population will double in less than 100 years• In some European countries, the growth rate is

so low that populations are actually declining

Birthrate

• The situation is quite different in other countries• More than two thirds of the world’s population live

in the tropical countries of Africa, South America, and Asia

• In some of these countries, the population continues to grow at an annual rate of about 3%

• Although this rate of growth appears to be low, it will double the present population in only 23 years

Deathrate

• The deathrate has decreased worldwide

• Over the past few hundred years, changes in agriculture have made more and better foods available throughout the world

• Improvements in the quality and availability of medical care have wiped out many deadly diseases and contributed to an increase in the life span of the average person

Effects of Human Population Growth

• A high birthrate, a low deathrate, and a longer lifespan all contribute to population growth

• As human populations grow, their effects on the environment also grow

• Countries with a rapidly growing population are often unable to produce enough food to satisfy the demand

Effects of Human Population Growth

• Today, scientists worry about the destruction of tropical forests

• Such devastation seems to be a high price to pay for farmland that is productive for only a few short years

• In addition, many of these tropical forests are often cleared by burning

• The burning produces large amounts of carbon dioxide, which is added to our atmosphere

Effects of Lifestyles

• It is not population growth alone that causes environmental problems

• After all, the rate of population growth in many industrial countries has actually slowed

• The lifestyle of a population also contributes to the extraordinary environmental demands made on the Earth

Effects of Lifestyles

• The population of the US is a good example– Population growth has stabilized at a low

level– We use more energy and natural resources

than any other country in the world– We own many consumer goods– Most families have two or more cars– Radios, TVs, etc. are staples of most modern

homes

Chapter 49: People and the Biosphere

Section 2: Pollution

Pollution

• Materials released into the environment fall into two categories: biodegradable and nonbiodegradable

• Materials that can be degraded, or broken down, by microorganisms into the essential nutrients from which they were made are biodegradable– Sewage, scraps of food

• Nonbiodegradable materials cannot be broken down by natural processes or are broken down only very slowly– Glass, plastics and metals, chemicals– Once these materials are released into the environment,

they remain there for a long time – sometimes forever

A consumer society produces extremely large quantities of wastes. However, some wastes can prove useful. These automobiles are valuable for the scrap metal they contain. And some household wastes can be recycled for further use.

Biological Magnification

• Sometimes pollutants affect the biosphere in ways no one expects

• Many primary producers pick up nonbiodegradable pollutants from the water

• They concentrate them and store them in their tissues• When herbivores eat producers, they too concentrate

and store these nonbiodegradable compounds in their tissues

• When carnivores eat herbivores, the compounds are further concentrated

Biological Magnification

• At each step in a food chain, the compounds are concentrated more and more

• In other words, the amount of the compounds in each organism in a food chain increases

• This phenomenon is known as biological magnification

• Biological magnification occurs with many pesticides and industrial waste products

If the plants in the pond in which this moose is dining have been contaminated by toxic materials, they may actually poison the moose. The concentrations of toxic chemicals in the plants will increase in the tissues of the moose.

The toxic chemicals DDT became part of many food chains when it was widely used as a pesticide. These falcon eggs show the dramatic effects of DDT poisoning.

Air Pollution

• The air supplies the oxygen our cells need to metabolize food and receives the waste products we give off as a result of our life processes

• But the air also contains many other chemicals—chemicals that are not part of the natural composition of the atmosphere

Smog

• If you live in a city, you may be familiar with the dirty-brown haze called smog

• Smog = smoke + fog

• Contains different pollutants in different places

• The causes of smog also differ from one location to another

Smog

• Weather conditions called temperature inversions can make smog a serious health hazard

• Normally, cooler air is at higher altitudes than warmer air

• The warmer air closer to the Earth’s surface contains pollutants

• But because it is warm, it is less dense than cool air and rises

• As it rises, it slowly cools, and the pollutants it contains are carried away by winds

Smog

• During an inversion, a layer of cool polluted air is trapped beneath a layer of warm air

• Because the cool air is denser than the warm air above it, it cannot rise

• As a result, the pollutants are kept near the ground

• Temperature inversions can last for hours, days, and even weeks

The skyline of Los Angeles, California, is barely visible through a curtain of smog. This city and many others like it depend upon automobiles and buses to move people from place to place. The vehicles produce waste gases that contribute to the formation of smog.

Acid Rain

• Certain pollutants in the air combine with water vapor to form droplets of acid

• When these droplets fall to the Earth in rain, the rain is called acid rain

• In many areas, the coal and oil burned in factories and power plants to generate energy contain large amounts of sulfur

• When sulfur is burned, it forms sulfur dioxide• Sulfur dioxide dissolves in water to form a strong

acid: sulfuric acid

Acid Rain

• Sulfur dioxide is often carried on prevailing winds far from where it is produced

• The effects of acid rain on the environment are numerous and serious to life

• Acid rain damages plants, rivers, lakes, etc.

Acid rain is a serious threat to the environment. Its effects on forest trees can be seen in this picture of evergreens that are now never green. Their needles have been burned off the branches by rains.

The Greenhouse Effect

• The amount of carbon dioxide in the atmosphere is increasing as a result of human activity in the biosphere

• Carbon dioxide is produced when carbon-containing fuels are burned

• Carbon-containing fuels include wood and charcoal as well as fossil fuels such as coal, oil, and natural gas

• Over the years, the burning of trees and fossil fuels for energy has released vast quantities of carbon dioxide into the atmosphere

The Greenhouse Effect

• Energy from the sun is absorbed by the Earth and changed into heat

• Later, this energy is radiated back from the Earth to the atmosphere

• Carbon dioxide and other gases in the atmosphere absorb this heat energy

– Greenhouse effect

The Greenhouse Effect

• As levels of carbon dioxide in the air increase, more heat is absorbed and the temperature of the Earth increases

• The effects of this global warming are unclear

– Melting of the polar icecaps

– Major changes in agriculture

Venus, although much like the Earth in many ways, has an atmosphere that consists mostly of carbon dioxide. As a result, Venus is considerably hotter than Earth. Scientists are concerned that the temperature of Earth will increase as levels of carbon dioxide in the atmosphere increase. If this happens, the huge polar ice caps will melt and sea levels will rise, flooding many coastal regions.

Holes in the Ozone Layer

• A layer of ozone exists far above the Earth in a part of the atmosphere called the stratosphere (10 – 30 miles above the Earth’s surface)

• Protects the Earth from harmful ultraviolet radiation from the sun

• Without the protection of this layer, few living things could survive

Holes in the Ozone Layer

• Scientists have recently discovered that the ozone layer is becoming thinner in certain places around the poles– Holes in the ozone layer

• The major cause of ozone depletion is a form of chemical air pollution that results from the addition of chlorofluorocarbons to the air

• Scientists predict that if the amount of UV radiation that reaches the Earth increases, the frequency of certain diseases—such as certain forms of skin cancer—will also increase

In this image, areas of low ozone concentration are in black/blue. The “hole” in the ozone layer extends over Antarctica and part of South America.

Water Pollution

• In the United States, billions of liters of fresh water are used daily– Drinking, cooking, bathing, cleaning

• Although water is a renewable resource, there is a limited amount of fresh water

• 75% of Earth is water• Only 3% is fresh water

– Only a small portion is available for living things– The greater portion is locked up in ice, mainly in polar ice

caps and glaciers• The most common sources of water pollution are chemical

wastes, raw sewage, and high temperatures

In many places in the world, the supply of drinkable water is severely limited. Here in Malawi, people fill buckets with water that is pumped from a communal well. These heavy buckets of water must be carried to their home.

Chemical Contamination

• Toxic chemicals can pollute water in two ways

– The chemicals can enter into streams and rivers

– Chemical wastes discarded on land can seep through the ground and enter the ground water supply

Sewage Contamination

• Sewage consists of large quantities of wastes that contain nitrogen compounds

• These compounds are used by bacteria in a process that requires oxygen

• If untreated sewage is added to rivers and streams, the number of bacteria increases dramatically

• These bacteria use up most of the available oxygen as they break down the nitrogen compounds

• Other organisms that live in the water may suffocate because their supply of oxygen is depleted

Sewage Contamination

• In rural areas, where homes are far apart, sewage is usually treated in septic systems

• In a septic system, bacteria work on the sewage, reducing it to water that is nearly pure

• This water seeps out of the septic system and into the ground

Sewage Contamination

• In cities, sewage must be treated in sewage treatment plants

• In special tanks, this sewage is broken down by bacteria

• Once the bacteria have decomposed the organic matter, chemicals that kill harmful microorganisms are added to the sewage and the treated water is released

Sewage Contamination

• Human sewage also contains many potentially harmful microorganisms: bacteria, viruses, and protozoa

• Filter-feeding organisms, such as clams and mussels, ingest the microorganisms and concentrate them in their tissues

• When these shellfish are eaten, diseases such as hepatitis, typhoid, and certain forms of dysentery can spread

Although almost three quarters of the Earth is covered by water, the supply of fresh water that is available for human needs is limited. It is extremely important to protect this water from becoming polluted.

Many cities and towns have sewage-treatment plants that process household waste water. In huge outdoor tanks, water is treated by chemicals and microorganisms.

Thermal Pollution

• Many factories and power plants produce heat as a waste product

• In the past, water from nearby rivers, lakes, or the ocean was used to cool such plants

• The water was pumped through pipes in the cooling system, where it absorbed heat

• The heated water was then pumped back into the environment

Thermal Pollution

• In some cases, heated water has no harmful effects on the ecosystem

• But often, heated water kills aquatic plants and animals

• This kind of water pollution is called thermal pollution

Water is often used by industries as a coolant. In this nuclear power plant, heated water is returned to the river from which it was pumped, causing a kind of pollution called thermal pollution. Thermal pollution is a danger to some forms of aquatic life.

Ocean Pollution

• For centuries people have dumped their wastes into the oceans

• Too many people produce too much waste, a great deal of which is nonbiodegradable

• Plastics and other wastes dumped into the oceans may float around for months or even years

• Large cities continue to dump so much sewage into the oceans that it cannot be degraded quickly enough

• Often, some of this sewage washes up on beaches

Ocean Pollution

• Pollution near the shore is a serious matter

• Some wastes dumped into the oceans—such as containers of disposable medical items—wash back onto shore, threatening the health of beach-goers

• Other wastes remain at sea, posing a hazard to ocean life

The solid wastes produced by consumer societies are often dumped into the oceans. This is devastating not only to ocean life, but also to beach-goers.

Oil Spills

• Regardless of the cause, once oil is spilled, it is difficult to remove

• Oil slicks are deadly to marine animals that swallow the toxic oil or become coated with it

• Toxic chemicals in oil often accumulate in those animals that are not killed immediately

• In most cases, these chemicals make the animal sterile• Some of the chemicals that accumulate in animal

tissue are potent carcinogens that may cause cancer in the people who eat them

Chapter 49: People and the Biosphere

Section 3: The Fate of the Earth

The Fate of the Earth

• People have always relied upon plants and animals for food, clothing, and shelter

• The survival of humans and human society depends upon the survival of other organisms in the biosphere

• Today, the survival of many of these organisms is threatened

Forests

• Wherever you live, your life is dependent upon forests in many ways

• Trees provide us with many essential products• Wood is used to make everything from pencils

to houses• Trees are a vital part of many ecosystems• The roots of trees keep the soil loose and at the

same time hold it in place, allowing rainwater to penetrate the soil without washing it away

Forests

• When forests are carelessly cut down, many important changes occur– Soil structure changes– Microorganisms die– Many small plants and animals can no

longer survive– Heavy rains wash away topsoil– Water table drops

Forests

• Many of our country’s few remaining old forests are being cut down at an alarming rate

• In tropical countries, rain forests are being destroyed so rapidly that they may disappear completely in 60 years

• Fortunately, government officials became aware of the problems associated with forest destruction

Forests

• Programs that plant new trees when old trees are cut down are called reforestation programs

– Vital to the health of the biosphere

These trees are no match for a chainsaw. Once cut, they will be used to make many consumer products. A tiny tree will be placed in its place.

Endangered Species

• When an animal or plant species becomes so rare that it is threatened with extinction, it is called an endangered species

• Species become endangered in several ways– Hunting– Are able to live in only one type of habitat

• Today, one plant or animal species becomes extinct every hour

Huge herds of bison roamed the Great Plains until hunters brought these awesome animals to the verge of extinction. Today, protected by strict laws, herds of these animals once again roam.

Why Save Endangered Species?

• Extinction is forever

• Many people feel that we have no right to cause the extinction of other species

– Scientists, biologists, activists, etc.

• But human needs are great, as are the demands on the ecosystem

Other animals have not been as lucky as the bison. The California condor is close to extinction. Captive breeding programs aim to keep this species alive. The black-footed ferret hunts prairie dogs. The population of ferrets is so small that their actual location in the wild is a closely guarded secret. The desert pupfish lives in small desert pools. If anything happens to its delicate habitat, it too will be in real danger of becoming extinct.

Useful Products

• Many everyday foods, medicines, and industrial compounds come from wild plant and animal species

• Antibiotics, heart drugs, anticancer medications, painkillers, and other important medicines are derived from plants

Useful Products

• No one knows the benefits that might be hidden in yet unknown plants that grow in tropical rain forests

• If these rain forests disappear, the potential contributions of their inhabitants to our society will also vanish

• Many animal species produce compounds that may prove important to human health– Sponges– Sea cucumbers– Horseshoe crab

Food from Plants

• Most of the world’s population obtains its food from crops grown on farms

• The crop plants grown in the US today are the results of generations of selective breeding

• When plant breeders develop a better variety, it is produced in enormous numbers and planted all over the country

• But planting a single variety can prove dangerous

Food from Plants

• Genetically similar plants are susceptible to the same diseases

• In some cases, people maintain seeds of crop varieties that are no longer commercially grown

• The genetic material in these seeds may become important if new crop varieties are wiped out by disease

• In other cases, crop breeders are constantly at work developing new disease resistant strains of crop plants

Food from Plants

• In many cases they cross crop plants with strains of wild plants that have more genetic variability

• So far, wild plants related to crop plants have provided the necessary “new genes” crop breeders want to introduce into already developed strains of crop plants

• Scientists all over the world regularly search for new wild species related to food crops

• But they face one serious problem: the destruction of natural habitats will destroy yet undiscovered wild plants

The tomato, eaten by many people, was once thought to be poisonous. In the past, the tomato grew in the wild. Today, the plant is commonly grown in many gardens. Who can tell how many other wild plants will be found in remote areas and what uses these plants may serve?

Chapter 49: People and the Biosphere

Section 4: The Future of the Biosphere

The Future of the Biosphere

• A lot of people agree that because Earth supplies us with all we need for life – food, water, air, and natural resources – we owe our planet the very best care possible

• In the past, people have treated Earth with neglect

• Today, attitudes are changing

Actions for Conservation

• There are people in the world who love wild places, wild plants, and wild animals

• There are also many people who understand how important the health of the biosphere is to the health of all species, including humans

• These people work together to protect the environment in many different ways

Actions for Conservation

• Towns, counties, states, the federal government, and conservancy groups have all purchased land that is to be set aside for conservation purposes

• The preservation of land habitats is one of the most important responsibilities we shall assume in the years ahead

• It is more difficult to conserve the resources in the ocean

• To conserve ocean species, the countries of the world must join together to protect the oceans and their inhabitants

Actions for Conservation

• Sometimes people work together to protect a single species

• For example, sports fisherman on the east coast have formed a group called Stripers Unlimited– A group that works to protect habitats

important to the striped bass– Larger organizations such as the Sierra Club,

World Wildlife Fund, and Green peace work on a national and international level to protect the environment

Difficult Decisions

• Cleaning up the environment and keeping it clean are not easy jobs

– Solid-waste disposal

– Sewage treatment plants

– Toxic waste

Difficult Decisions

• In overwhelming numbers, Americans are expressing their fears for the future of planet Earth

• You must decide how important the environment is and whether you are willing to pay to keep it healthy