Environmental Science
T/F: the human population has grown faster in the 20th century than it ever has before
true
The rapid growth in what has caused environmental problems all around the world?
human population
demography
study of populations, but most often refers to the study of human populations
what do demographers study?
historical size and makeup of the populations of countries in order to make comparisons and predictions; they also study properties that affect population growth such as economics and social structure.
2 general categories of countries in terms of demography
developed countries and developing countries
developed countries
higher than average incomes, slower population growth, diverse industrial economies
developing countries
lower average incomes, simple and agriculture based economies and rapid population growth
exponential growth
Occurred in the 1800’s, meaning population growth rates increased during each decade
what caused the expenential growth of the 1800’s?
increases in food production, improvements in hygeine that came with the industrial and scientific revolutions
Is it likely that the earth can continue to sustain exponential growth in the future?
no
what are the 4 properties that scientists use to predict population sizes?
age structure
survivorship
fertility rates
migration
population pyramid
a type of double sided bar graph that shows typical age structures for countries that have different rates of growth
Countries that have high rates of growth usually have what?
more young people than old people
Countries that have slow growth or no growth usually have what?
an uneven distribution of ages
survivorship
percentage of members of a group that are likely to survive to any given age
how is survivorship studied?
studies a group of people born at the same age and notes when each person dies
survivorship type I
most people live to be very old
survivorship type II
people have a similar death rate at all ages
survivorship type III
usually very poor human populations in which many children die
fertility rate
number of babies born each year per 1000 women in a population
total fertility rate
average number of children a woman gives birth to in her lifetime
when did the total fertility rate drop below the replacement level in the US?
1972, the first time in US history; the rate remained below replacement level for most of the 1990’s
replacement level
the average number of children each parent must have in order to replace themselves in the population
Why did the population of the US continue to grow from 1970 to 2000?
baby boomers had kids and immigration
Why has human population increased dramatically in the past 200 years?
death rates have declined more rapidly than birth rates (less people are dying that being born)
why have death rates declined?
adequate food supply, clean water, safe sewage, vaccines
life expectancy
the average number of years members of a population are likely to live
what affects life expectancy the most?
infant mortality (death rate of infants less than 1 year old)
what was the worldwide life expectancy in 1900?
40
what was the worldwide life expectancy in 2000?
67
what was the life expectancy in many developed countries now?
80+
infant health is affected by what?
parents access to education, food, fuel, clean water. if these needs are met, most children will survive
threats to life expectancy arise as population becomes denser
contagious diseases such as AIDS and TB can spread quickly
T/F: in most developed countries populations have stopped growing
true
demographic transition
a model that describes how economic and social changes affect population growth rates; compares birth rates, death rates, and population sizes during the 4 stages of transition
4 stages of demographic transition
preindustrial, transitional, industrial, postindustrial
preindustrial stage (1)
birth rate and death rate both high, population stable
transitional stage (2)
population explosion occurs, death rates decline as hygeine, nutrition and education improve
industrial stage (3)
population slows, because birth rates slow. birth rate and death rate are about the same so the population stabilizes (but the population is still much larger than stage 1)
postindustrial stage (4)
birth rate drops below replacement level, so population decreases
how much is the earth’s population growing per year?
75 million
infrastructure
basic facilities and services that support a community (water supplies, sewer lines, power plants, roads, subways, schools, hospitals)
symptoms of overwhelming population growth
suburban sprawl, overcrowded schools, polluted rivers, barren land, inadequate housing (what happens when population uses resources faster than they can be renewed)
shortage of fuelwood
people can’t boil water, they start to cut down living trees which can lead to deforestation
unsafe water
can cause disease, people use same water to bathe, drink, sewer disposal
arable land
land that can be used to grow crops
urbanization
movement of people from rural areas to cities
where is most of the world’s population now?
Asia
what strategies do governments use to limit population growth?
public advertising, family planning programs, economic incentives, legal punishments
population of the world
6 billion
population prediction for 2050
9 billion
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