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Earth’s Population Growth Limits to growth and consumption •Resource consumption at an all-time all time high and continuing to rise •Population growth at an unprecedented high Questions •How many people can the Earth hold? •Are A there th a fi finite it amountt off resources? ? •Do we have enough land to support agriculture? •What What is the FATE of our resource dependent society? Population Growth Rate Average population growth rate ~0.02%/yr Toba Caldera Super Eruption Evolution Bottleneck •We have a lack of diversity y in our mitochondrial DNA •There is more genetic diversity in an average band of chimpanzees than in the entire human race. •Humanity went through a rather slim bottleneck about 74,000 years ago. Environmental affects on population Population Growth Rate Demographic Transition Doubling Times = 70 %g growth rate/year y Growth Rate (%/yr) Doubling Time 0.02 3,500 0.5 140 1 70 1.4 50 2 35 5 14 7 10 10 7 17 4 A Average population l ti growth th rate t ~0.02%/yr Population Growth Rate 6,261,118,623 6 261 118 623 - 2004 6,361,827,322 – 2005 6,776,311,884 Growth today ~ 1.2% Doubling g time 58 y years http://blue.census.gov/cgi-bin/ipc/popclockw Demographic Transition Population percentage by region Land Surface Area ~1.5x1014 m2 Population threshold ~ 529 trillion people shoulder to shoulder @1 1.3%/yr 3%/yr it would take 900 years to reach this population Environmental Impact I = PAT P = Population size per-capita p consumption p A = Affluence – p T = Environmental Damage inflicted by the g to supply pp y consumption p technologiesused Earth’s Carrying Capacity The carrying capacity of an ecosystem is the "maximum population size of a species that an area can support without reducing its ability to support the same species in the future future" •Estimates range from ~ 1 billion to 1 trillion people •Range of medians from 7 7.7 7 to 12 billion people Complicated by: -differences in type and quantity of resources -rapid cultural evolution of resources usage Earth’s Carrying Capacity The carrying capacity of an ecosystem is the "maximum population size of a species that an area can support without reducing its ability to support the same species in the future future" # of Births p per woman World p population p in 2150 1.6 children 3.6 billion 2.0 children 10.8 billion 2.6 2 6 children hild Present average 27 billi billion Earth’s Carrying Capacity The carrying capacity of an ecosystem is the "maximum population size of a species that an area can support without reducing its ability to support the same species in the future future" A sustainable population of humans on Earth implies: --renewable energy sources combined with --socially sustainable standards of living. What is relationship between Standard of living and carrying capacity? The current global population exceeds the median range of socially and biophysically sustainable carrying capacity estimates. Exceedance of Earth's carrying capacity is made possible by consumption of nonrenewable energy sources, such as fossil fuels as well as inequities in global distribution of food and energy consumption. Earth’s Carrying Capacity Resource Consumption Earth’s Carrying Capacity Earth’s Carrying Capacity Human impact on the environment. · Six million acres of prime farmland – an area the size of Vermont – were lost in the U.S. alone between 1982 and 1992. Four of those six million acres were lost to urban and suburban expansion. The other 2 million acres were lost through erosion caused by deforestation, unsustainable farming practices, and animal over-grazing. · Fresh water is essential to health, economic development, and life itself. With increasing numbers of people, people the amount of fresh water available to each person decreases decreases. Only 0.3% of the water on the planet is available for human use. Due to mismanagement, over 40% of the groundwater in the U.S. is contaminated by industrial, agricultural, and household pollution, making it extremely difficult and costly to purify. · As human population increases, the diversity and number of plants and animals decreases. We lose one or more entire species of animal or plant life every 20 minutes – some 27,000 species a year. This is a rate and scale of extinction that has not occurred in 65 million years. · The global emission of carbon dioxide has quadrupled since 1950, largely from deforestation and the burning of fossil fuels. Researchers say this greenhouse gas causes global warming and disruption in weather patterns. Five storms over the span of five years have cost the insurance industry in the United States $25 $25.7 7 billion billion. · 1.8 billion people live in 40 countries with critically low levels of forest cover. By 2025, this number could nearly triple to 4.6 billion. Women often bear the burden of forest scarcity, walking farther for wood, carrying loads long distances, or suffering a variety of ills associated with cooking where wood is scarce. Case study – Easter Island Effects of overuse of natural resources ~165 km2 Effects of overuse of natural resources