CK-12 Biology I - Honors
Page 79
Does Earth have a carrying capacity for humans? Recall that carrying capacity is the maximum population size that a particular environment can support without habitat degradation. Ideally, carrying capacity matches population size to resource availability. Although the human population is clearly continuing to grow, many scientists believe that we over-consume resources and exceed the environment’s capacity to cycle nutrients and process waste. They believe that multiple factors will contribute to a crisis in which disease, starvation, or global conflict will cause a population crash or even extinction:
Our current agricultural system, globally transformed by the Green Revolution of the mid-20th century, depends heavily on nonrenewable fossil fuels for fertilizers, pesticides, and irrigation. Ecologist and agriculturalist David Pimentel predicts that to avert disaster, the U.S. must reduce its population to a maximum of 200 million (we are now above 300 million – see the “pop clock” Figure below), and the world population must drop to 1/3 its current level. Distribution of food has long been a problem and today has some rather ironic consequences: A 2006 MSNBC report claimed, "There are an estimated 800 million undernourished people and more than a billion considered overweight worldwide."
Figure 17.36
The U.S. population passed 300 million on October 17, 2006. Agriculturalist David Pimentel believes the U.S. must lower its population by 1/3 to prevent a crisis caused by inability to continue our fossil fuel-dependent agricultural practices. U.S. and World Population Clocks are maintained by the U.S. Census Bureau online at:
Both developing and developed countries depend almost entirely on petroleum to fuel industrialization and transportation, as well as agriculture. In 1956, geophysicist Marion Hubbert predicted that world oil production would peak about half a century into the future and then decline, initiating a global crisis. Predictions about the consequences of Peak Oil range from successful development of alternative fuels, to collapse of the global industrialized economy, to intense nationalism and war. Some analysts, such as energy banker Matthew Simmons, believe that the Peak has already occurred (Figure below). Others, like energy industry consultants Wood McKenzie, believe we will not reach the peak for another ten years. The difference does not seem significant, but ten years would allow more time for development of alternative fuels and institution of conservation measures.
Figure 17.37
Oil production outside OPEC and former Soviet Union countries has already peaked, according to oil industry data bases for 2003 and 2004.
Fresh water supplies are declining due to pollution and overuse. According to the United Nations, 2.6 billion people lack water for sanitation, and 1.1 billion have inadequate supplies of safe drinking water. Irrigation and overuse have seriously reduced groundwater supplies, and water pollution threatens biodiversity as well as human sources. Waterborne diseases and lack of water for sanitation cause up to 80% of human illness. Growing populations, of course, will worsen this water crisis.
Habitat destruction due to agriculture, urban sprawl, and mining is the number one cause of extinction today, precipitating a biodiversity crisis. The World Resources Institute estimates that agriculture has displaced 1/3 of all temperate and tropical forests and ¼ of all grasslands; in the U.S., less than 2% of native prairie ecosystems remain. Stephen Hawking calculates that continuation of the last 200 years’ rate of population growth would have us all standing shoulder-to-shoulder, literally.
Burning fossil fuels has brought about atmospheric change.
Sulfur and nitrogen emissions cause acid rain, which destroys fish, lakes, forests, and limestone structures. CO2 emissions lead to global warming. Earth's surface air temperatures have risen 0.74°C (1.33°F) during the last 100 years, and will continue to rise by 1.1 to 6.4 °C (2.0 to 11.5 °F) by 2100, according to the Intergovernmental Panel on Climate Change (IPCC).
Food, oil, water, land, and air crises support the idea that our human population has already grown beyond carrying capacity with respect to environmental degradation. As world population continues to grow, what can we do to avert famine, disease, or war? How can we prevent a crash? What should be our goal?
Fortunately, individuals, organizations, and governments are beginning to address these problems. The concept of sustainability as a goal for human activities may hold promise for economic, social, and environmental decision-making. Although the term is recent, the concept is clearly expressed in the Great Law of the Iroquois Confederacy:
"In our every deliberation we must consider the impact of our decisions on the next seven generations." http://en.wikiquote.org/wiki/Native_American_proverbs
A sustainable activity or state can be maintained indefinitely, without compromising resources for the future. Sustainability of products and services considers complete life cycles – raw materials, manufacturing, transportation/distribution, use and re-use, maintenance, recycling and ultimate disposal. All phases must address conservation of natural and human resources and also biodiversity. Many people believe current population and lifestyles are not sustainable. Unequal distribution of resources suggests that developing countries may accelerate pressure on resources in order to improve their own lifestyles.
A preliminary tool for estimating sustainability is an ecological footprint analysis. Your ecological footprint is the amount of land area you would need to sustain your current lifestyle. Footprint analysis considers the resources you consume and the pollution you generate, and then calculates the amount of land which would be needed to produce equivalent renewable resources and process associated with waste. Air, land, water, food, and energy resources are all incorporated into the model. You can estimate your own footprint online (see Links at the end of the lesson) and compare it to that of countries throughout the world (Figure below). Note that the average U.S. footprint is 12 times that of India, 24 times that of Somalia, and 4.4 times the world average. The last figure is worth expressing in another way: to provide everyone alive today with our western lifestyle, we’d need 4 or 5 backup planets.
Figure 17.38
Ecological footprints measure the amount of land area required to sustain (produce replacement resources and assimilate waste) particular lifestyles. Note the 24-fold difference between citizens of Somalia and those of the US. One U.S. acre is equal to 0.405 hectares.
To date, there is no overall agreement on a carrying capacity of Earth for humans, but many people are concerned about population growth, resource depletion and environmental degradation. Joel E. Cohen, in his book How many people can the earth support? summarizes three potential responses to the “population problem” identified at the beginning of the chapter. All three can contribute to the ultimate solution.
“Make a bigger pie.” Use technology and innovation to create, conserve, and distribute resources.
“Put fewer forks on the table.” Through birth control and cultural change, reduce both population size and lifestyle expectations.
“Teach better manners.” Transform political and social structures toward the goal of social justice.
The human population, like all populations, has the capacity to reproduce exponentially and yet must live within a finite world. Unique among animals, however, we can utilize technology, cultural planning, and values in decisions which influence our future welfare. Which tools would you choose? What decisions will you help to make?
Lesson Summary
According to Neo-Malthusians, the worldwide human population may have already passed Earth’s carrying capacity in terms of environmental degradation, resource depletion, and unbalanced distribution of food, wealth, and development. More people will increase the danger of famine or war.
According to the cornucopians, technology and innovation can solve any problems which arise due to human population growth. The more people, the better.
The demographic transition model suggests that human populations pass through four stages of population growth:
Stage 4: Eventually, birth rate equals death
rate, growth rate is zero, and the population stabilizes.
Stage 3: With industrialization, urbanization and contraception, births fall, and growth begins to decline.
Stage 2: Development and sanitation reduce death rates, so populations grow exponentially.
Stage 1: Growth is slow and uneven, because high death rate offsets high birth rate.
Because this model uses late 18th and 19th century European data, it correlates closely with demographic transitions throughout developed nations into the 20th century, but may not fit undeveloped countries.
No country remains in Stage 1.
A number of poor, undeveloped countries remain in stage 2; age pyramids show large youth populations.
Many countries have entered Stage 3, with some lowering fertility rates by as much as 40%, but pyramid “youth bulges” mean they continue to grow.
Replacement fertility varies from country to country because death rates vary.
A few countries have reduced fertility rates below replacement and are shrinking in population.
Shrinking countries may for a time experience economic difficulties related to an aging population.
In September 2007, world population stood at about 6.7 billion, growing by 211,090 people each day.
The last billion-person increase took only 12 years.
Despite recent declines in birthrate in some developed countries, the human population will continue to increase at least until a peak in 2050 of 9.4 billion people or more.
Many scientists believe that we humans have already overshot the carrying capacity of Earth if resource exploitation and habitat alteration are considered.
Five factors which many believe already limit sustainable human population size are:
Agricultural dependence on nonrenewable fossil fuels for fertilizers, pesticides, and irrigation.
Dependence of industry and transportation on a finite fossil fuel supply, which has already peaked.
Decline in freshwater resources due to pollution and overuse.
Habitat destruction due to urban sprawl and agriculture, and a consequent biodiversity crisis.
Atmospheric changes such as acid rain and global warming – both consequences of increased fossil fuel burning.
The concept of sustainability may hold promise for economic, social, and environmental decisions.
Sustainability of products and services considers complete life cycles from raw materials to disposal.
A tool for estimating sustainability is the ecological footprint.
The average U.S. footprint is 12 times India’s, 24 times Somalia’s, and 4.4 times the world average.
Were all people to adopt a U.S. lifestyle, we would need 4 or 5 planets to supply resources and dispose of waste sustainably.
Potential solutions to the problems of population growth are summarized by Joel E. Cohen:
Create new and conserve existing resources – the technological “fix.”
Lower population size and lifestyle expectations – cultural change.
Distribute resources equitably – social justice.
Review Questions
Describe the overall pattern of human population growth, beginning with our origins 200,000 years ago and compare it to the exponential and logistic models.
Compare the factors that influenced human population growth up to the first 1 billion mark to those which controlled growth of the last billion.
Summarize the 5 stages of the demographic transition model in terms of b, d, and r.
Explain the problems with the original, four-stage demographic transition model of human population growth. Give examples of each.
Explain why replacement fertility must exceed 2 children per female.
Use the “pop clock” links at the end of the chapter to look up the current US and world populations. Compare these to predictions for 2050 made by the UN and U.S. Census Bureau. Why do many people consider these numbers to be above Earth’s carrying capacity?
Summarize 5 environmental effects of human activity which may act as limiting factors for population growth. How many of these relate to our use of fossil fuels, and why is this a problem?
Explain how ecological footprints measure sustainability, and compare them for developed and undeveloped nations.
Explain what Joel E. Cohen meant by suggesting that “a bigger pie,” “fewer forks,” and “manners” are needed to address the problems of overpopulation.
Consider what you know about resource limitations, population distribution, levels of consumption, technology, poverty, economics, political realities, religious views, and different human perspectives on the earth. Choose and describe 3 changes you believe would be most successful in solving the problems of worldwide population growth – and 3 changes you believe would be least successful. Support each change with reasons why you think it would be more or less effective.
Further Reading / Supplemental Links
Joel E. Cohen, How Many People Can the Earth Support? Norton, 532 pp, 1995.
http://www.bradshawfoundation.com/journey
http://desip.igc.org/mapanim.html
http://www.eoearth.org/article/Human_population_explosion
http://www.globalchange.umich.edu/globalchange2/current/lectures/human_pop/human_pop.html
http://www.census.gov/main/www/popclock.html
http://www.bestfootforward.com/
http://www.footprintnetwork.org/gfn_sub.php?content=footprint_overview
http://www.panda.org/news_facts/publications/living_planet_report/index.cfm
http://www.worldchanging.com/archives/006904.html
http://lca.jrc.ec.europa.eu/lcainfohub/introduction.vm
http://www.ilea.org/leaf/richard2002.html
Vocabulary
carrying capacity
The maximum population size that a particular environment can support without habitat degradation.
cornucopian
A person who believes that people and markets will find solutions to any problems presented by overpopulation.
demographic transition theory
Theory that proposes that human populations pass through 4 or 5 predictable stages of population growth.
density-dependent factor
Factor which has the potential to control population size because its effects are proportional to population density.
density-independent factor
Factor which may affect population size or density but cannot control it.
ecological footprint
The amount of land area needed to sustain a particular lifestyle, matching its resource consumption and pollution to necessary renewable resource production and waste assimilation.
exponential model (geometric or J-curve)
A model of population growth which assumes that growth rate increases as population size increases.
k-selected species
Species which have adaptations which maximize efficient utilization of resources, conferring competitive strength near or at carrying capacity.
logistic (S-curve)
A model of population growth which assumes that the rate of growth is proportional to both population size and availability of resources.
Neo-Malthusians
Individuals who believe that human population growth cannot continue without dire consequences.
population
A group of organisms of a single species living within a certain area.
r-selected species
Species which have adaptations which maximize growth rate, r.
replacement fertility
The number of births per female required to maintain current population levels; includes 2 children to replace the parents and a fraction of a child extra to make up for early mortality and sex ratio differences at birth.
Points to Consider
Now that you have studied some of the data on human population growth, return to the questions in the introduction to this lesson and consider whether or not your
answers have changed.
Are we built for growth – or for efficient use of resources?
Does our growth pattern resemble a J, or an S? Why?
Do you think Earth has a carrying capacity for humans?
Do you think we are we in danger of extinction?
What exactly is our “population problem,” and what do you think we should do to solve it?
Jared Diamond, reflecting on the fates of past societies facing problems of sustainability, in Collapse: How Societies Choose to Fail or Succeed (2005), p. 522, says: "Two types of choices seem to me to have been crucial in tipping … outcomes towards success or failure: long-term planning, and willingness to reconsider core values. On reflection, we can also recognize the crucial role of these same two choices for the outcomes of our individual lives." Do you think the worldwide human population will be able to make these choices wisely?
Chapter 18: Ecology and Human Actions
Lesson 18.1: The Biodiversity Crisis
Lesson Objectives
Compare humans to other species in terms of resource needs and use, and ecosystem service benefits and effects.
Define the concept of biodiversity.