27.1. Human Population and Industrialization (p. 472)
A. Introduction
1. The exponential growth of the human population since the Industrial Revolution has been dramatic.
2. Modern agriculture and medicine have increased growth rates; over 90 million people are added each year.
3. The United Nations estimates a human population of 10 billion by the end of the twenty-first century. (Fig. 27.1a)
4. MDCs and LDCs are the two major groups of countries.
a. The more developed countries (MDCs) industrialized first.
b. MDCs include the United States, Canada, Japan, Russia, Australia, New Zealand, and all of Europe.
c. MDCs have 22 percent of the world's population but consume about 80 percent of the world's energy and resources.
d. Waste and pollution are also greater in proportion to use of resources.
e. Less developed countries (LDCs), therefore, have 78 percent of the population but use only 20 percent of resources.
f. Most people in the LDCs have a lifestyle far below that of the MDCs.
g. If LDCs strive to achieve the MDC lifestyle, consumption and waste may exceed earth's carrying capacity.
B. By-products of Industrialization
1. Industrialization is driven by energy consumption from coal, petroleum, and natural gas. (Fig. 27.1b)
a. Fossil fuels were formed by decomposition and pressure on remains of plants and animals millions of years ago.
b. Oil is the fuel most widely used, both as starting material for making gasoline and for other products.
2. Pollution is any environmental change that adversely affects the lives and health of living things.
a. Burning fossil fuels results in hydrocarbons, carbon, nitrogen and sulfur oxides, particulates. (Table 27.1) (Fig. 27.2) [transp. 144]
b. Automobiles consume one-third of the world's production of oil and are the chief source of air pollution.
c. Some estimate there will be four times more automobiles in the world in 2025.
d. Industrially produced halogens and the use of nitrogen fertilizers also influence the atmosphere.
e. These sources are considered nonrenewable since they are in limited supply.
3. Sources of energy that are relatively nonpolluting exist.
a. Solar energy does not add additional heat to the atmosphere; solar panels absorb and move rooftop heat.
b. Photovoltaic (solar) cells produce energy directly from sunlight.
c. Falling water is used to produce electricity in hydroelectric dams.
d. Geothermal energy derived from heat in the earth's core heats water to heat buildings, generate electricity.
e. Wind power can pump water or generate electricity.
f. These sources are all considered renewable since they are replenished by physical means.
4. The increase in human population threatens both human well-being and biodiversity.
a. Conservation biology is a branch of science directed at environmental problems.
b. Science can study the value of biodiversity and help manage ecosystems.
c. Study of the human impact on the global environment raises ethical questions.
27.2. Global Climate Change (p. 474)
A. Climate Fluctuation
1. Earth's climate fluctuates; we are currently between ice ages, and today's climate was last seen 130,000 years ago.
2. Some scientists are concerned that global climate will warm at a rate ten times faster than in the past.
a. In 1850, atmospheric CO2 was about 280 parts per million (ppm); today, it is about 350 ppm.
b. This increase is due largely to burning of fossil fuels and clearing of forests.
c. Oceans currently absorb half of the CO2 emitted or else the atmospheric level would be higher.
d. Methane given off by oil and gas wells, rice paddies, cows, etc. is increasing by one percent a year.
e. Greenhouse effect is warming of lower atmosphere caused by accumulation of certain greenhouse gases that allow rays of the sun to pass through, but then reflect or reradiate heat to the earth. (Fig. 27.3a) [transp. 145]
f. The following greenhouse gases would contribute to warming:
1) carbon dioxide (CO2), produced by fossil fuel and wood burning;
2) nitrous oxide (NO2), produced by fertilizer use and released from decomposition of animals wastes;
3) methane (CH4), produced by bacteria (especially in animal guts), in sediments, and in flooded rice paddies;
4) chlorofluorocarbons (CFCs), in particular Freon (a refrigerant); and
5) halons (halocarbons; CxFxBrx), released from fire extinguishers.
g. Water vapor is also a greenhouse gas since clouds reradiate heat back to earth.
h. Water vapor, CO2 and methane played a critical role in making the earth warm enough to allow life to evolve.
i. Analysis of gas trapped in Arctic ice shows earth's temperature fluctuated in the past, according to levels of CO2 and methane.
j. Greenhouse gases differ in their ability to absorb specific wavelengths of infrared radiation.
1) CO2 may be absorbing as much heat radiation as it can; therefore, adding other gases may have more effect.
2) Greenhouse effectiveness of methane is about 25 times greater than that of carbon dioxide.
3) Nitrous oxide is about 200 times more effective than carbon dioxide.
k. The global climate appears to have risen about 0.6o C since the industrial revolution.
l. Some computer models predict a rise of from 1.5o C to 4.5o C by 2060. (Fig. 27.3c)
B. Predicted Consequences
1. The ecological effects of a rise in global temperature would be noticeable.
2. As oceans warm, temperatures in polar regions would likely rise to a greater degree than other areas.
3. Glaciers would melt and sea levels would rise due to melting and expansion of warm water.
4. Water evaporation would increase with increased rainfall along coasts and dry conditions inland.
5. Droughts would reduce agricultural productivity and trees would die off.
6. Expansion of forests into Arctic areas would not likely offset loss of forests in temperate zones.
7. Coastal agricultural lands and deltas in Bangladesh, India, and China would be inundated.
27.3. Global Chemical Climate (p. 476)
A. Rainfall pH (Fig. 27.4)
1. Pure water has a pH of 7; dissociation of H2O produces equal numbers of H+ and OH- ions.
2. Atmospheric CO2 combines with water to produce a weak carbonic acid and an increased number of H+ ions.
3. Rain normally has a pH of 5.6 rather than 7.0.
4. However, near urban areas, rainfall pH is nearer 4.0 and some fog clouds drop to as acidic as 1.7!
5. Living vegetation and building limestone rapidly deteriorate under such "acid rains."
B. Sources
1. Coal and oil routinely burned by power plants emit sulfur dioxide (SO2) into the air.
2. Kuwait oil has high sulfur content; the oil well fires released much sulfur dioxide (SO2) into the atmosphere.
3. Automobile exhaust contributes nitrogen oxides to the air.
4. Both sulfur dioxide and nitrogen oxides are converted to acids when they combine with water vapor in the air.
5. Sulfur and nitrogen oxides are emitted in one locale; deposition occurs in another location across boundaries.
6. Acid deposition is responsible for the following:
a. killing lakes and forests in North America and Europe;
b. killing small invertebrates and decomposers and threatening the ecosystem;
c. reducing agricultural yields;
d. causing extensive structural damage by corroding marble, metal, and stonework;
e. degrading water supplies by leaching heavy metals from the soil into drinking-water supplies; and
f. statistically is implicated in increases in lung cancer and colon cancer.
C. Photochemical Smog
1. Photochemical smog is air pollution that contains nitrogen oxides (NOx) and hydrocarbons (HC), which react in the presence of sunlight to produce ozone (O3) and peroxylacetyl nitrate (PAN).
2. Both NOx and hydrocarbons come from fossil fuel combustion, but additional hydrocarbons come from various other sources as well, including paint solvents and pesticides.
3. Breathing O3 affects respiratory and nervous systems, results in respiratory distress, headache, and exhaustion.
4. Ozone is damaging to plants, resulting in leaf mottling and reduced growth.
5. Carbon monoxide
a. Carbon monoxide (CO) is a gas that comes from burning of fossil fuels in the industrial regions.
b. High levels of CO increase the formation of ozone (O3).
c. CO combines preferentially with hemoglobin and prevents hemoglobin from carrying oxygen.
d. CO over Southern Hemisphere, from burning of tropical forests, is equal to that over the Northern Hemisphere.
6. Thermal inversion
a. Normally, warm air near the ground rises and dissipates into the upper atmosphere.
b. Air pollutants, including smog and soot, are sometimes trapped near earth due to a thermal inversion.
c. Thermal inversion occurs when a layer of dense cold air is trapped under a layer of warm air.
d. Areas around hills are susceptible because air stagnates, with little mixing. (Fig. 27.5)
27.4. Stratospheric Ozone Depletion (p. 478)
A. The Earth's Atmosphere
1. The troposphere is the lower atmosphere that envelops us at ground level.
2. The stratosphere is "upper atmosphere."
B. The stratosphere contains the ozone shield.
1. The ozone shield is a layer of ozone (O3) in the stratosphere, some 50 km above the earth's surface.
2. It absorbs much of the ultraviolet (UV) radiation of the sun, preventing it from reaching the earth's surface.
3. In the history of life, ozone shield permitted life on land to exist; aquatic organisms are shielded by water.
4. Hazards of UV radiation include increased mutation rate, which can lead to skin cancer and cataracts; depression of immune system; impaired crop and tree growth; and death of plankton.
5. It became apparent in the 1980s that some depletion of worldwide ozone had occurred.
6. By the 1990s, there was an annual loss of 40-50% of ozone above Antarctica, an ozone hole, every spring. (Fig. 27.6)
7. Development of ozone holes depends on complex atmospheric conditions.
8. U.N. Environment Program predicts a 26 percent rise in cataracts and nonmelanoma skin cancers for every 10 percent drop in ozone; this is 1.75 million cases of cataracts and 300,000 more cases of skin cancer every year.
9. The cause of ozone depletion can be traced to the release of chlorine (Cl-) atoms in the stratosphere.
a. Chlorine atoms combine with ozone and strip away oxygen atoms one by one.
b. One atom of chlorine destroys up to 100,000 molecules of ozone before settling to earth's surface.
c. Chlorine atoms come from breakdown of CFCs, which were in heavy human use from 1950 to 1990.
d. Freon is a common CFC used in refrigerators and air conditioners.
e. Other CFCs occurred in cleaning agents, production of plastics, and as spray can propellants.
f. Most countries have agreed to stop use of CFCs by 2000; CFCs in atmosphere will remain for a century.
27.5. Surface Waters, Aquifers, and Oceans (p. 479)
A. Fresh water is required for domestic purposes, including drinking, crop irrigation, industrial use, and energy production.
B. Freshwater needs are supplied by surface water from lakes and rivers, and from underground aquifers.
C. Pollution of Surface Waters
1. Pollution contributes to the shortage of fresh water.
2. Solid wastes include household trash, sewage sludge, agricultural residue, mining refuse, and industrial waste.
3. Point sources are identifiable sources of pollution; nonpoint sources are caused by runoff, etc.
(Fig. 27.7)
4. The U.S. spends $9 billion a year on cleanup but only $200 million yearly to prevent pollution.
5. Recycling may save industry money and prevent much pollution.
D. Sewage
1. Sewage treatment plants degrade organic wastes, which would otherwise cause oxygen depletion in lakes.
2. Human feces contains pathogens that cause cholera, typhoid fever, and dysentery; these kill many children.
3. Sewage treatment plants use bacteria to break down organic matter into inorganic nutrients.
4. Nutrients accelerate natural processes by which bodies of water fill in, called cultural eutrophication.
E. Agricultural and Industrial Wastes
1. Nitrate levels
a. Intensive animal farming or the presence of many septic tanks releases ammonium (NH4+) from wastes.
b. This is converted by bacteria to soluble nitrate that moves through the soil to water supplies.
c. Between 5-10% of all wells in the U.S. have nitrate levels higher than the recommended maximum.
2. Industrial wastes
a. Industrial wastes include heavy metals and organochlorides, such as some pesticides.
b. These are not degraded in nature or in normal sewage treatment, and accumulate in deltas.
c. When these wastes enter water, they are subject to biological magnification. (Fig. 27.8)
[transp. 146]
1) Decomposers are unable to break down these wastes, and they are not excreted.
2) The molecules, therefore, remain in tissues and are passed up the food chain to the next consumer.
3) They become more concentrated at each level in the food chain.
4) Since aquatic food chains have more links, biological magnification is greater.
5) Where humans are final consumers, human milk can contain detectable amounts of DDT and PCB.
3. Aquifer pollution
a. Previously, industry ran wastewater into a pit from which pollutants could seep into the ground.
b. Wastewater and chemical wastes were also injected into deep wells.
c. Both practices are being phased out; there are few alternatives for industry to dispose of wastes.
F. Pollution of Oceans
1. The oceans are the final recipients of wastes deposited in rivers and along the coasts.
2. Waste dumping occurs at sea, and ocean currents sometimes transport both trash and pollutants back to shore.
3. Solid pollutants cause death of birds, fish, and marine mammals that mistake them for food and get entangled.
4. Offshore mining and shipping add pollutants to the oceans.
a. Five million metric tons of oil a year, over one gram per 100 square meters of ocean surface, ends up in oceans.
b. Large oil spills kill plankton, fish larvae, and shellfishes, as well as birds and marine mammals.
c. The Exxon Valdez oil spill in Alaska's Prince William Sound leaked 44 million liters of crude oil.
d. In Gulf War, 120 million liters were released from damaged onshore storage tanks in the Persian Gulf.
e. Petroleum is biodegradable; takes a long time because low-nutrient content does not support bacteria.
5. Some species of fish are in dramatic decline from combined effects of pollution and overfishing.
27.6. Soil Erosion, Desertification, and Deforestation (p. 482)
A. City Populations Increase
1. In 1950, 20 percent of the world population lived in cities; by 2000 it is predicted that 60 percnet will live in cities.
2. As new housing is built around new cities, it takes over agricultural land.
3. Expanded urbanization also degrades the environment.
B. Soil Erosion and Desertification
1. In agricultural areas, wind and rain carry away about 25 billion tons of top soil yearly, worldwide.
2. At such a rate, it is estimated that practically all top soil will be lost by the middle of the next century.
3. Soil erosion causes a loss of productivity; it is compensated for by fertilizers, pesticides, and fossil fuel energy.
4. One solution is to employ strip-cropping and contour farming to control soil erosion.
5. Desertification is transformation of marginal lands to desert conditions due to overgrazing and overfarming.
a. This is most evident along the southern edge of the Sahara Desert in Africa.
b. Over 240,000 square miles of once-productive grazing land has become desert in the last fifty years.
c. A similar process can occur if U.S. rangeland is overgrazed.
C. Deforestation
1. In Canada, vast stands of trees are scheduled to be felled for paper, wood products and particleboard.
2. Tropical rain forests are more biologically diverse than temperate forests.
a. U.S. temperate forests contain about 400 species of trees; a typical 10-hectare rain forest contains 750 species.
b. South American streams contain about twice the species found in all of the U.S. and Canada.
3. A N.A.S. study estimates a million species are in danger of disappearing in 20 years due to deforestation.
4. Lost species that have never been studied may have been sources of food or medicine.
5. Logging in tropical forests meets the demand for furniture and also the desire of local people to farm the land.
6. Slash-and-burn agriculture also contributes to the destruction of tropical rain forests.
a. The ashes provide temporary nutrients to raise crops.
b. After a few years, the fertility of the land is insufficient to raise crops and farmers move on.
c. Cattle ranching usually takes over from farming.
d. Pig-iron industry in Brazil also requires wood charcoal to smelt the pig iron.
27.7. Human Impact on Biodiversity (p. 484)
A. Types of biodiversity
1. Species biodiversity is the variety of species of bacteria, plants, animals, etc.
2. Genetic variation is a finer level of biodiversity that helps maintain reproductive vitality and assists adaptation.
3. Community biodiversity refers to the variation in communities in which species may live.
B. Extinction
1. There have been several natural mass extinctions in the history of earth followed by recovery.
2. Recovery from the last mass extinction resulted in the highest level of biodiversity the earth has known.
3. Human activities that reduce biodiversity began about 30,000 years ago with killing off of large animals.
4. Hunting contributes to the estimated extinction of 15,000 to 30,000 species a year. (Fig. 27.11)
5. Fish stocks are being depleted by overfishing.
6. Commercial trade causes exploitation of tigers, cheetahs, leopards, jaguars, etc. for furs; sharks for fins; rhinoceros for rhino horn powder; elephants for tusks for ivory; and cacti for gardeners.
7. Habitat destruction
a. A major cause of extinction is the loss of habitat to support a species.
b. The habitat for a species may be totally destroyed through natural events or human activities.
c. Habitats may be fragmented into small pieces that cannot support the population.
d. By 2010, very little undisturbed rain forest will exist outside of national parks.
8. Introduced species
a. Accidental or purposeful introduction of new species can cause extinction of endemic species.
b. Introduction of brown tree snake to Guam has resulted in extinction of nine of eleven native bird species.
c. The carp, an Asian fish that can tolerate polluted waters, is now more prevalent than our native fish.
9. Pollution
a. Global climate change may be so rapid that many species cannot adjust.
b. Biological magnification of pesticides has reduced predatory bird populations.
c. Acid deposition is implicated in the worldwide decline in amphibian populations.
C. Conservation Biology
1. Conservation biology is a discipline that brings together many fields to attempt to solve biodiversity problems.
2. It attempts to develop practical approaches to preventing extinction of species and destruction of ecosystems.
3. Most conservation biologists believe biological diversity is good and each species has a value all its own.
4. Sustainability is concept that it is possible to meet economic needs while protecting environment.
5. Some economists argue that as per capita income increases, environmental degradation first increases, then decreases as people become affluent enough to begin to protect the environment.