Environmental Problems, Their Causes, and Sustainability 1

take the resources of 1.15 planet earths to indefinitely supportour current use of renewable resources!The ecological footprint of each person in developedcountries is large compared to that in developingcountries (Figure 1-7, left). The per capita ecologicalfootprint of the United States is nearly double the country’sbiological capacity per person—explaining whythe country spreads its ecological footprint by importinglarge quantities of renewable resources from othercountries. You can estimate your ecological footprintby going to the website www.redefiningprogress.org/.Also, see the Guest Essay by Michael Cain on the websitefor this chapter.This eventually unsustainable situation is expectedto get worse as affluence increases in both developedand developing countries. According toWilliam Rees and Mathis Wachernagel, developers ofthe ecological footprint concept, it would take the landarea of about four more planet earths for the rest of theworld to reach U.S. levels of consumption with existingtechnology. Clearly, such consumption patternscannot be sustained.A new country with a large and growing ecologicalfootprint is emerging. China has the world’s largestpopulation and hopes to increase its total and per capitaeconomic growth, which will increase the ecologicalfootprints of its people. See the Guest Essay on thistopic by Norman Myers on the website for this chapter.What Are Nonrenewable Resources?Resources We Can DepleteNonrenewable resources can be economicallydepleted to the point where it costs too much toobtain what is left.Nonrenewable resources exist in a fixed quantity orstock in the earth’s crust. On a time scale of millions tobillions of years, geological processes can renew suchresources. But on the much shorter human time scaleof hundreds to thousands of years, these resources canbe depleted much faster than they are formed.These exhaustible resources include energy resources(such as coal, oil, and natural gas that cannot berecycled), metallic mineral resources (such as iron, copper,and aluminum that can be recycled), and nonmetallicmineral resources (such as salt, clay, sand, and phosphatesthat usually are difficult or too costly to recycle).Figure 1-8 shows the production and depletioncycle of a nonrenewable energy or mineral resource.We never completely exhaust such a resource, but it becomeseconomically depleted when the costs of extractingand using what is left exceed its economic value. Atthat point, we have six choices: try to find more, recycleor reuse existing supplies (except for nonrenewable energyresources, which cannot be recycled or reused),waste less, use less, try to develop a substitute, or waitmillions of years for more to be produced.Resource productionArea under curveequals the totalamount of theresourceSome nonrenewable mineral resources, such ascopper and aluminum, can be recycled or reused to extendsupplies. Recycling involves collecting wastematerials, processing them into new materials, andselling these new products. For example, discardedaluminum cans can be crushed and melted to makenew aluminum cans or other aluminum items thatconsumers can buy. Recycling means nothing if we donot close the loop by buying products that are madefrom or contain recycled materials. Reuse is using a resourceagain in the same form. For example, glass bottlescan be collected, washed, and refilled many times.Recycling nonrenewable metallic resources takesmuch less energy, water, and other resources and producesmuch less pollution and environmental degradationthan exploiting virgin metallic resources.Reusing such resources takes even less energy andother resources and produces less pollution and environmentaldegradation than recycling.1-4 POLLUTIONTimeEconomic depletion(80% used up)Figure 1-8 Full production and exhaustion cycle of a nonrenewableresource such as copper, iron, oil, or coal. Usually, a nonrenewableresource is considered economically depleted when80% of its total supply has been extracted and used. Normally,it costs too much to extract and process the remaining 20%.Where Do Pollutants Come From, and WhatAre Their Harmful Effects? Threats to Healthand SurvivalPollutants are chemicals found at high enough levelsin the environment to cause harm to people or otherorganisms.Pollution is the presence of substances at high enoughlevels in air, water, soil, or food to threaten the health,survival, or activities of humans or other organisms.Pollutants can enter the environment naturally (for example,from volcanic eruptions) or through human oranthropogenic activities (for example, from burningcoal). Most pollution from human activities occurs inor near urban and industrial areas, where pollutionsources such as cars and factories are concentrated.Industrialized agriculture is also a major source ofhttp://biology.brookscole.com/miller1411