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Essentials of the Living World Second Edition George B. Johnson Jonathan B. Losos Chapter 23 Planet Under Stress Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 23.1 Pollution • Our world is one highly interactive biosphere and damage done to any one ecosystem can have ill effects on many others biologists call widespread effects on the worldwide ecosystem global change the pattern of global change that has become evident within recent years is one of the most serious problems facing humanity’s future 23.1 Pollution • Pollution takes many forms air pollution is a major problem in the world’s cities • some cities, such as New York and Boston, are gray-air cities because of sulfur oxides from industrial pollution • other cities, such as Los Angeles, are brown-air cities because pollutants in the air react with sunlight to form smog water pollution • despite improved methods of sewage treatment, lakes and rivers are becoming increasingly polluted with sewage • fertilizers and insecticides also get washed from the land to the water 23.1 Pollution • Large quantities of many toxic chemicals, although no longer manufactured, still circulate in the ecosystem for example, chloronated hydrocarbons, a class of compounds that includes DDT, have all been banned for normal use in the US • these chemicals break down slowly and accumulate in animal fat tissue • as they pass through the food chain, they become increasingly concentrated in a process called biological magnification Figure 23.1 Biological magnification of DDT 23.2 Acid Precipitation • Acid rain is pollution-acidified precipitation produced when sulfur products of industry combine with water vapor in the air and then fall back to earth as rain or snow acid precipitation destroys life • at least 1.4 million acres of forests in the Northern Hemisphere have been adversely affected • Tens of thousands of lakes in the northeastern US and Canada are dying biologically as their pH levels fall below 5.0 industrial scrubbers and the Clean Air Act revision of 1990 have begun to address this problem 23.3 The Ozone Hole • Living things were able to leave the oceans and colonize the surface of the earth only after a protective shield of ozone had been added by photosynthesis the ozone shield protects the earth from harmful radiation starting in 1975, the earth’s ozone shield began to disintegrate, leaving a mysterious zone of lower-thannormal ozone concentration • this zone is called an ozone hole Figure 23.4 The ozone hole over Antarctica 23.3 The Ozone Hole • Chlorofluorocarbons (CFCs) were found to be responsible for the breakdown of ozone originally thought to be harmless, these chemicals are used as coolants in refrigeration and cooling, gas in aerosol contains, and as the foaming agent in Styrofoam CFCs easily catalyze the conversion of O3 (ozone) into O2 the drop in worldwide ozone is now over 3% and is estimated to have led to an increase in perhaps as much as 20% in lethal melanoma skin cancers 23.4 Global Warming • Industrial society’s burning of fossil fuels has released huge amounts of carbon dioxide into the atmosphere the chemical bonds in CO2 transmit radiant energy from the sun but trap the longer wavelengths of infrared light (or heat) this creates a greenhouse effect of this trapped heat other greenhouse gases include CFCs, nitrogen oxides, and methanes Figure 23.5 The greenhouse effect 23.4 Global Warming • The earth’s greenhouse effect is intensifying global warming is a rise in the average global temperatures associated with increased CO2 concentration in the atmosphere some possible effects of global warming include • changes to rainfall patterns • increases in agricultural yield but increased risks of drought • melting of ice in glaciers and the polar ice caps, causing sea level to rise 23.5 Loss of Biodiversity • Current rates of extinction are alarmingly high, constituting a crisis in biodiversity biologists have identified three factors that play a role in extinction • habitat loss – this is the single most important cause • species overexploitation – species that are hunted or harvested by humans have historically been at risk of extinction • introduced species – the introduction of exotic species results in extinction because these species have no native predators to keep their populations in check Figure 23.6 Factors responsible for animal extinction Figure 23.7 Extinction and habitat destruction 23.6 Reducing Pollution • The pattern of global change that is overtaking our world is very disturbing • We must quickly find ways to reduce the harmful impact of human activities on the biosphere • It is important that four areas be addressed reducing pollution finding other sources of energy preserving nonreplaceable resources curbing population growth 23.6 Reducing Pollution • Economists have now identified an “optimum” amount of pollution based on how much it costs to reduce pollution versus the social and environmental costs of allowing pollution if more pollution than the optimum are allowed, the social cost is too high if less than the optimum is allowed, the economic cost is too high Figure 23.8 Is there an optimum amount of pollution? 23.6 Reducing Pollution • Two approaches have been devised to curb pollution in the US antipollution laws are designed to curb pollution by setting stiff standards for what can be released into the environment pollution taxes are assessed in order to balance the conflicting demands of environmental safety and economic growth 23.7 Finding Other Sources of Energy • The pollution generated by burning coal and oil, the increasing scarcity of oil, and the potential contributions of CO2 to global warming, all make it desirable to find alternative energy sources there are many possible candidates including • nuclear power • solar power • wind power Alternative Energy Sources Figure 23.9 Three Mile Island nuclear power plant Figure 23.10 Alternative energy sources 23.8 Preserving Nonreplaceable Resources • In the US, there are three sorts of nonreplaceable resources that are being reduced at alarming rates topsoil • over one quarter of topsoil has been lost since 1950 groundwater • groundwater in aquifers is being depleted or polluted biodiversity • loss of species creates instability in ecosystems and reduces productivity Figure 23.12 Tropical rainforest destruction 23.9 Curbing Population Growth • The world population reached 6.5 billion people in 2004 and will double in about 58 years such growth cannot continue because our world cannot support it slowing population growth will help sustain the world’s resources but per capita consumption is also important Figure 23.13 Growth curve of the human population Figure 23.15 Distribution of population growth 23.9 Curbing Population Growth • Human population growth is not occurring uniformly over the planet the rate at which a population can be expected to grow in the future can be assessed graphically by means of a population pyramid Table 23.1 A Comparison of 2003 Population Data in Developed and Developing Countries Figure 23.17 Population pyramids 23.9 Curbing Population Growth • The AIDS epidemic in Africa will have a huge impact on population sizes • In sub-Saharan Africa, AIDS has reduced life expectancy at birth by 20 years Figure 23.18 Projected AIDS effect on Botswana population (year 2025) 23.9 Curbing Population Growth • We in the developed countries need to pay more attention to lessening the impact of our resource consumption an ecological footprint is the amount of productive land required to support an individual at the standard of living of a particular population through the course of his or her life • the ecological footprint of an individual in the US is 10X greater than that of someone in India 23.10 Preserving Endangered Species • Once you understand why a particular species is endangered, it becomes possible to think of designing a recovery plan habitat restoration captive propagation sustaining genetic diversity preserving keystone species conservation of ecosystems Recovery Plans Figure 23.20 Habitat restoration Figure 23.21 Sustaining genetic diversity Figure 23.22 Preserving keystone species 23.11 Individuals Can Make the Difference • One person can make a difference in solving environmental problems for example, many US families recycle Figure 23.23 Cleaning up the Nashua river Inquiry and Analysis • What fraction of the 155 years do not deviate from the 1961 - 90 mean value? • Has the global air temperature been warming progressively over the last century and a half? Graph of History of Changes in Global Air Temperature