Lecture 25: Human Population Growth

1. Lecture 25: Human Population Growth EEES 3050

2. Human Impacts • Today - Human population growth. • Thursday – Largest humans threats to biodiversity • Both impact earth’s ecosystem services.

3. What are ecosystem services? • The processes through which ecosystems and the species they contain help sustain human life. • Examples

4. Examples • Purification of air and water (e.g. wetlands) • Mitigation of drought or water • Generation and preservation of soils • Detoxification and decomposition of wastes • Pollination Dispersal of seeds • Nutrient cycling • Control of agricultural pests • Maintenance of biodiversity • Protection of shorelines from erosion • Protection from u.v. • Partial stabilization of climate • Moderation of climate extremes • Provision of aesthetic beauty

5. Human Impacts • What effects the level of environmental impact by humans? • Population #

6. Population Explosion • When was the world’s pop’n at 1 billion? • 1830 • 1930: 2 billion • 1960: 3 billion • 1975: 4 billion • 1999: 6 billion • 2007 ? • 2046: 10 billion • UN projections: plateau 7-15 B by 2100

7. UN projections • plateau 7-15 B by 2100 • basis for international policy decisions • Potential limiting resources • food and water • agricultural maximum 10-12 B (sustainable?) • distribution challenges (today!) • modern agriculture is NOT sustainable • heavy petrochemical reliance • Are there new technologies on the horizon?

8. Population Growth

9. Reasons for explosion • < 1800: preindustrial times = high death rates • disease (especially for children) • plagues • famine (agriculture ca. 10,000 y BP) • > 1800: Louis Pasteur & the germ theory = declining death rates • environmental controls • vaccinations • antibiotics (1930 — penicillin) • high birth + declining death = growth

11. A dip in the growth rate from 1959-1960, for instance, was due to the Great Leap Forward in China. During that time, both natural disasters and decreased agricultural output in the wake of massive social reorganization caused China's death rate to rise sharply and its fertility rate to fall by almost half.

12. When are populations stable? • Birth rates = death rates. • In human pop’s has occurred at two levels, • Both high • Both low.

13. Demographic Transition • Shift from high fertility and mortality to low fertility and mortality • Phase I: high fertility and mortality • Phase II: high fertility and low mortality • Phase III: fertility begins to fall • Phase IV: new population stability attained

14. Demographic Transition • What causes these transitions? • the transition is social, not external • now apparent in 80% of human populations

15. Demographic Transition

16. Reasons for transition in demographics • Decline in death rates: • technological • Decline in birth rates: • behavior/social • increasing wealth (weak direct correlation) • access to contraceptives (very strong, direct correlation) • increased female education (strong, direct correlation)

17. Falling Fertility

18. Human Population: The Next Half Century • Joel E. Cohen • Science, 2003, Nov. • A columnar growth pyramid suggest: • Slow growth • If each cohort is larger than the previous: • Rapid growth

19. Cohen Predictions for 2050: • Population will be larger by 2 to 4 billion people, • more slowly growing • declining in the more developed regions • more urban, • 2 major demographic uncertainties in the next 50 years: • International migration • structure of families. • Economies, nonhuman environments, and cultures (including values, religions, and politics) strongly influence demographic changes. • Human choices, individual and collective, will have demographic effects, intentional or otherwise.

20. Population Benefits • Benefits of expanding population • Human society provides “positive feedback” in creativity & technology! • Labor force: creating wealth • Population growth often correlated with economic growth.

21. Population Costs • Costs of expanding population • There is no evidence that a population can continue to grow. • All studies of population growth result in an asymptote, sometimes following a crash.

22. Human Impacts • What effects the level of environmental impact by humans? • Population # • Lifestyle, i.e. consumption • Ecological regard • Impact = (Population x Lifestyle) / Ecological Regard • Principle of ecosystem sustainability: • populations do not exceed critical resources

23. Population growth and consumption • Ecological footprint: • Compare the amount of land and water that is appropriated to produce all the resources a nation (or individual) consumes and absorb the waste it generates. • What is your ecological footprint?

24. Ecological Footprint (1997)

25. Ecological Footprint • Interesting points: • World already in deficit in 1997. • USA, Europe, Japan in deficit. • Countries with highest populations today were “sustainable” in 1997. • Where are they now? • New Zealand has high ecological footprint.

26. Population growth and consumption • What ecological concepts are associated with population growth and consumption? • Carrying capacity. • Have we reached K? • What is different about human populations? • Natural populations reach saturation: intrinsic control • Human capacity is externally controlled • (distinction usually ignored) • We can redistribute resources. • Technology

27. Carrying Capacity

28. Lots of people • How does the human population growth and consumption impact the ecological world? • Ecology is… • The study of the interactions that determine the distribution and abundance of organisms. • Climate change • Landuse change • Movement of species • Spread of disease • Use of resources, such as? • Fish, NPP, Land, Forests (particularly Tropics), Extraction • Pollution • Etc.

29. Impacts of Human Population Growth • Use of NPP • Disease – Malaria • Water resources • Energy • Household size

30. Global patterns in human consumption of net primary production. • Nature. June 2004. Inhoff et al.

31. One measure of humanity’s cumulative impact is • the fraction of the planet’s net primary production that we appropriate for our own use. • What effects does our human appropriation of net primary production alter? • the composition of the atmosphere, • levels of biodiversity • energy flows within food webs • the provision of important ecosystem services.

34. Changing patterns of HANPP will have important consequences for human welfare and global biodiversity. • Further growth and development in areas of high HANPP is likely to impoverish local ecosystems and diminish the vital services they provide. • Will require increased NPP imports, alterations to flows of NPP-based products and exertions of greater pressure on ecosystems elsewhere. • Improved technologies may reduce HANPP through better efficiencies and product substitutions. • Spatially explicit measures of HANPP enable: • Illumination of current human impacts on the biosphere • Monitoring changes in these impacts over time • exploring the potential of various policies for alleviating them.

35. The economic and social burden of malaria • Jeffrey Sachs*† & Pia Malaney • Nature, Feb. 2002

37. Observation: • As a general rule of thumb, where malaria prospers most, human societies have prospered least.

39. Poverty is concentrated in the tropical and subtropical zones • Same geographical boundaries that most closely frame malaria transmission. • The extent of the correlation suggests that malaria and poverty are intimately related. • average GDP in malarious countries in 1995 was US$1,526, compared with US$8,268 in countries without intensive malaria

40. They are correlated, but is there a cause? • primary school students miss 11% of school days per year because of malaria, • malaria can affect cognitive abilities in ways ranging from subtle to profound • E.g. children with malaria are found to have poorer nutritional status than non-malarial children an outcome that can impair brain development • Relation to population growth? • If there is high child mortality, what is the expected results? • One theory predicts that a high burden of malaria will lead to a disproportionately high fertility rate and an overall high population growth rate in regions of intense malaria transmission.

41. Global Water Resources: Vulnerability from Climate Change and Population Growth • Charles J. Vorosmarty, Pamela Green, Joseph Salisbury, Richard B. Lammers • Science July 2000.

42. Goal is to identify the contributions of climate change, population growth, and their combination to the future state of global water resources • How would climate affect global water resources? • Population growth?

43. Compared Domestic, Industrial and Agricultural usage to Discharge (Q) • = DIA/Q • Discharge is… • the volume of water that flows in a given period of time. • Which is more important? • Population change or climate change

45. Methods: • Global change models • Changes discharge • Population growth models • Changes population numbers

48. Results • We conclude that impending global-scale changes in population and economic development over the next 25 years will dictate the future relation between water supply and demand to a much greater degree than will changes in mean climate • In short: • Population change more important than climate change.