Population: Look here: census/main/www/popclock.html

1. Population: Look here: http://www.census.gov/main/www/popclock.html

2. World population has risen sharply • Global human population was < 1 billion in 1800. • Population has doubled just since 1964. • We add ~2.5 people every second (78 million/year).

3. Population growth rates, 1990–1995 • Growth rates vary from place to place. • Growth peaked at 2.1% in the 1960s; it has now declined to 1.2%.

4. Fertility rates affect population growth rates Total fertility rate (TFR) = average number of children born per woman during her lifetime (Replacement fertility = the TFR that keeps population size stable) For humans, replacement fertility is about 2.1.

5. Population size: Future projections Demographers project population growth trends to estimate future population sizes. Different fertility rate scenarios predict global population sizes in 2050 of 8 billion, 9.15 billion, or 10.5 billion. All these projections assume fertility rates below today’s; at today’s rate, the population would reach 11 billion.

6. The “IPAT” model Shows how Population, Affluence, and Technology interact to create Impact on our environment. • I = P  A  T Further factors such as Sensitivity and Education can be added to the original equation to make it more comprehensive. Impact on the environment is usually either pollution or resource consumption.

7. Modeling population and its consequences Some models show population growth leading to resource depletion, which can result in declining food production, industrial output, and population.

8. Increasing our carrying capacity Technology has allowed us to raise Earth’s carrying capacity for our species time and again. Tool-making, agriculture, and industrialization each enabled humans to sustain greater populations.

9. Population size: National populations Nations vary from China’s 1.3 billion down to Pacific island nations of 100,000. Shown are the 15 most populous countries, and selected others; 2005 data.

10. Population density and distribution Humans are unevenly distributed, living at different densities from region to region.

11. Sex ratios A population’s sex ratio can affect its growth rate. The naturally occurring sex ratio in humans is 105 to 106 males for every 100 females. This may be an evolutionary adaptation as males are slightly more prone to death at any given age. The ratio of men to women is therefore approximately equal at reproductive age.

12. Factors affecting population growth rates Population growth in any country/region depends on rates of birth, death, immigration, and emigration (people leaving). (birth rate + immigration rate) – (death rate + emigration rate) = population growth rate

13. Migration can have environmental effects Immigration and emigration play large roles today. Refugees from the 1994 Rwandan genocide endured great hardship, and deforested large areas near refugee camps.

14. Global growth rates have fallen The annual growth rate of the world population has declined since the 1960s. (But the population size is still rising!)

15. Demographic transition theory Demographic transition = model of economic and cultural change to explain declining death rates, declining birth rates, and rising life expectancies in Western nations as they became industrialized. (See diagram in a few slides) Proposed by Frank Notestein in the 1940s–1950s

16. Demographic transition: Stages The demographic transition consists of several stages: Pre-industrial stage: high death rates and high birth rates. Transitional stage: death rates fall due to rising food production and better medical care. Birth rates remain high, so population surges.

17. Demographic transition: Stages, continued Industrial stage: birth rates fall, as women are employed and as children become less economically useful in an urban setting. Population growth rate declines. Post-industrial stage: birth and death rates remain low and stable.

18. Demographic transition: Stages

19. Demographic fatigue and demographic transition Many governments of developing countries are experiencing “demographic fatigue,” unable to meet the social, economic, and environmental challenges imposed by rapid population growth. This raises the question: Will today’s developing countries successfully pass through the demographic transition?

20. Female education and TFR Female literacy and school enrollment are correlated with total fertility rate. More-educated women have fewer children.

21. Family planning and TFR Family planning, health care, and reproductive education can lower TFRs. The Matlab Project provided visits from local women offering counseling, education, and free contraceptives.

22. Poorer countries will experience most future population growth 98% of the next billion people born will live in developing nations.

23. Population and the environment Population growth can lead to environmental degradation. Overpopulation in Africa’s Sahel region has led to overgrazing of semi-arid lands.

24. Affluence and the environment Poverty can lead to environmental degradation… BUT wealth and resource consumption can produce even more severe and far-reaching environmental impacts.

25. Global ecological footprint Scientists have calculated the global ecological footprint now exceeds what the Earth can bear in the long run. Remember what this is called?

26. The wealth gap Residents of developed nations have larger houses, more possessions, and more money than residents of developing nations. The richest 20% of the world’s people consumes 86% of its resources, and has > 80 times the income of the poorest 20%.

27. HIV/AIDS and human population AIDS cases are increasing rapidly worldwide.

28. HIV/AIDS and human population 38 million people have HIV/AIDS. Infects 1 in 5 people in southern African nations Kills babies born to infected mothers Has orphaned 14 million children • Has cut 19 years off life expectancies in parts of southern Africa