Issue 2 CARRYING CAPACITY AND ECOLOGICAL FOOTPRINT KEY QUESTIONS BACKGROUND CARRYING CAPACITY

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1 CARRYING CAPACITY AND ECOLOGICAL FOOTPRINT Issue 2 KEY QUESTIONS in What factors keep natural populations in balance? What does carrying capacity mean? Can scientists determine the carrying capacity of Earth? Of the United States? Of your hometown? What is an ecological footprint? BACKGROUND As he developed his theory of evolution by natural selection, Charles Darwin observed that for any species, more individuals are born than will survive to reproduce. If resources are unlimited and environmental conditions are ideal, the number of offspring reaches a maximum. This state of highest reproductive power, which varies widely among different organisms, is known as a population's biotic potential. However, a number of factors, collectively known as environmental resistance, prevent populations from reaching their full biotic potential and thus growing explosively. Environmental resistance includes disease, predation, drought, temperature extremes, lack of food, and other adverse physical or chemical conditions. Most of these factors are density-dependent: that is, their effects are most pronounced when the population density the number of individuals in a given area increases beyond a certain level. Thus, the interplay between biotic potential and density-dependent environmental resistance keeps a population in balance. CARRYING CAPACITY An important ecological concept related to this balancing act is carrying capacity. Carrying capacity is the maximum number of individuals of a given species that an area's resources can support in the long term without significantly depleting or degrading those resources. For humans, this definition is expanded to include (1) not degrading our cultural and social environment and (2) not harming our physical environment in ways that would adversely affect future generations.' Determining carrying capacities for most organisms throughout the animal and plant kingdoms is, at least in theory, a reasonably direct calculation. However, when carrying capacity is used in a human context, the discussion may become contentious and the resultant calculations subject to dispute. Why is this so? 'Bouvier, L., & L. Grant How Many Americans? (San Francisco: Sierra Club Books). 43

2 44 PART Two Population and Migration First, some would argue that the term "human carrying capacity" is meaningless. According to Simon and Kahn, "Because of increases in knowledge, the earth's 'carrying capacity' has been increasing... to such an extent that the term... has by now no useful meaning."2 Second, because air and water pollution do not recognize political boundaries, some scientists define the environment occupied by humans and the resources used by them as a global, rather than a regional or national, entity. For them, only a single estimation of human carrying capacity the Earth's is valid and meaningful. Third, carrying capacity for nonhuman species is calculated by using numerical data and mathematical models. But the assessment of human carrying capacity involves scientists, economists, policy makers, sociologists, theologians, and so forth. These groups often disagree when it comes to defining key carrying capacity concepts. Finally, other organisms are typically limited by their food supply in a particular region, but humans can import food, if one does not consider the Earth as a single region. Similarly, humans can export waste and pollution by air and water to areas outside their immediate surroundings. Also, by buying raw materials or manufactured goods from outside their region, some humans can avoid the environmental impact of producing the materials themselves. THE IMPACT OF POPULATION As you can see, carrying capacity is a complicated subject. Nevertheless, the human carrying capacity of the Earth, or a portion thereof, can be estimated, granted that different populations have different impacts based on their technology, consumption, and ethics, as well as the simple number of individuals. For example, 100 million people with a vegetarian diet would have a different environmental impact compared with 100 million people who consume meat. One way to assess this impact is to compare how vegetarian and meat-eating populations affect water supplies. About 1,000 tons of water are required to produce 1 ton of grain. Globally, 40 percent of all grain goes to meat and poultry production.3 Thus, high levels of meat consumption put additional stresses on global water supplies. In terms of energy production and consumption, the impact of industrialized countries varies widely. France generates nearly 80 percent of its electricity by nuclear power and has a significantly different regional energy/environmental impact than China, which generates electricity largely with coal and as of 2005 was just beginning to require emission controls on new power plants. When estimating global or regional human carrying capacity, scientists study environmental changes, as well as the rate that these changes occur. Some useful indicators of environmental change include the rate of topsoil loss (see Issue 19), the rate of species loss, the rate of degradation of water quality (Issue 11), and the rate of change in the composition of the atmosphere (Issues 5 and 6). And finally, carrying capacity may ultimately have less to do with population density and more to do with a society's technology, resource demand, and waste. ASSESSING CARRYING CAPACITY In mid-2006 the population of the United States was nearly 300 million.4 Can our own natural resources successfully support 300 million people? How do the imported goods that 2Simon, J., & H. Kahn The Resourceful Earth (Malden, MA: Blackwell Publishers). 3Postel, S Dividing the Waters: Food Security, Ecosystem Health, and the New Politics of Scarcity (Washington, DC: Worldwatch Institute). 4U.S. Bureau of the Census, U.S. POPClock Projection (

3 ISSUE 2 IIII Carrying Capacity and Ecological Footprint 45 maintain our level of economic activity and standard of living affect the global environment? How fast is our population growing? Which segment of our population is growing the fastest? How much of our growth is due to legal immigration? Illegal immigration? Obviously, the precise human carrying capacity of an area is very difficult to determine, especially for a country as large and diverse as the United States. Despite the difficulty, it is useful to estimate human carrying capacity so that policy makers can act to ensure that our environment is able to support human life and natural biodiversity into the future. Question 2-1: Select one of the items in the following list and write a few sentences arguing that it is a carrying capacity issue, and then argue that it is not. a. Die-offs of squirrels on your campus b. The loss of 70,000 km2 of cropland each year due to nutrient depletion c. Increasing vehicular traffic and "road rage" incidents d. Record high prices for heating oil and natural gas in recent winters in the northeast United States and elsewhere

4 46 PART Two Population and Migration e. Rapidly rising real estate prices in California and coastal communities f. The loss of 50 percent of wetlands in twenty-two states since colonial times Question 2-2: What indicators, environmental or otherwise, would support the assertion that the United States had exceeded its carrying capacity? One possible example: export of hazardous waste to developing countries. Question 2-3: It has been stated that everyone in the United States could fit comfortably inside the state of Texas. The mid-2006 United States population was 299 million. The area of Texas is 261,914 sq. mi. (67,835,000 ha). Calculate how many acres, and hectares each person would occupy if all U.S. residents (in 2006) lived in Texas (1 mi2 = 640 acres; 1 acre = 0.4 ha). ECOLOGICAL FOOTPRINT Another way of examining the impact of humans is to estimate the individual impact each of us has, a measure known as our ecological footprint. Every individual has an ecological footprint that extends well beyond the geographical area in which that person lives. The

5 ISSUE 2 Carrying Capacity and Ecological Footprint 47 Ecological Footprint of Nations5 gives estimates for how much of the Earth's area we appropriate for our "needs." The average American, for example, uses 10.3 ha (25.4 acres) to support his or her lifestyle. This includes farmland, forests, mines, dumps, schools, hospitals, roads, playgrounds, malls, etc. (see Figure 2-1). Question 2-4: How many times larger would Texas need to be, assuming all Americans lived there and each American required 10.3 hectares? Question 2-5: The surface area of the Earth is 15 billion hectares. Calculate the area available for each of Earth's 6.52 billion inhabitants as of Report your answer in hectares and acres. What assumption did you use? FIGURE 2-1 Aerial photo of a mall in Charleston, SC. To comply with local zoning regulations, shopping centers must have a minimum number of paved parking spaces, which contributes to the large ecological footprint of Americans. (Courtesy of South Carolina Coastal Conservation League) 5Venetoulis, J., D. Chazan, & C. Gaudet, at footprintnations2004.pdf.

6 48 PART Two Population and Migration Question 2-6: Now assume all 6.52 billion people lived like Americans. How much area would be needed? Report your answer in hectares and acres. How many more planets with the surface area of Earth would be required? Question 2-7: How much area would be required for all 6.52 billion people if they lived like the 150 million residents of Pakistan, who each require 0.8 hectare? Of course, not all of the Earth's surface can serve as footprint area. Approximately 6.4 billion hectares are marginally productive or unproductive, since they are covered by ice or lack water. Additionally, 36.3 billion hectares are covered with seawater. Question 2-8: Summarize the major points of this Issue. Question 2-9: Discuss the carrying capacity of the United States from the standpoint of sustainability.

7 ISSUE 2 Carrying Capacity and Ecological Footprint 49 FOR FURTHER THOUGHT Question 2-10: Americans use a disproportionate portion of the Earth's resources. Discuss reasons why this is so. Question 2-11: Question 2-12: Question 2-13: Discuss whether the use of resources by Americans is a fair allocation of the planet's resources. Is our use of resources sustainable? Why or why not? Cite specific examples and document your assertions with evidence. Because estimating an area's human carrying capacity is inexact and difficult, some would argue that the concept is useless. Do you agree or disagree? Explain and justify your answer. Question 2-14: Conduct a search on the Web using the key words "ecological footprint." Once you have accessed a suitable site, calculate your footprint. How does your ecological footprint compare to others? What actions could you take to reduce your footprint?