Human Population as an Environmental ProblemUltimately the greatest environmentalthreat that mankind has created.

Two factors contribute together:1)The sheer number of people2)The impact of each person on the environment.

By the numbers…

By the late 90’s, the world population wasapproximately 5.9 billion people.

The annual growth rate is estimated worldwide at about 1.4%

At this rate, 82.6 million people are addedto the population each year.

Approximately 90% of the populationgrowth occurs in developing countries in Asia, Africa, and South America.

The average pop. growth in these areaswas 1.7%, whereas in N. America andEurope the rate is closer to 1%, and in some cases, much lower.

Thomas Malthus

British economist, predicted that the sizeof the population would outstrip the capacity of Earth to feed the population.

Reasoned that it would be impossible to maintain a rapidly growing population on a finite resource base.

Malthus’ three premises:1) Adequate food is necessary for survival.

2) “Passion between the sexes is necessaryand will remain nearly in its present state”.Therefore many children will continue to beborn.

3) The power of population growth is“Greater than the power of Earth to produce subsistence.”

One Thing Malthus didn’t count on:

Technology has allowed us to gain a higheryield from agriculture.

Technology has also allowed us to live inever greater densities, and still manage to keep “pestilence and plague” down (at least in some areas).

Birth control, which allows some control over the birth rate.

What Malthus never could have envisioned:

Although Mathus did not see the great expansion of technology, his basic ideasabout populations was correct.

The advent of technology allowed the population to increase, but also increased the effect of the population on the environment.

Technology causes:1)An increase in the use of resources.2)Different uses for resources, and different effects on the environment.

Ex: -Use of fossil fuels as a resource -CFC’s in the atmosphere -water pollution, acid rain

An Ironic Twist of Facts…

One of the principals of international aidis that of raising the “standard of living”.usually involves the introduction oftechnology.

This runs counter to a second principle,which is to lower the population growth rate.

=Fewer people, but still a larger impact.

Demography: the study of populations

There are a number of key characteristicsthat define what a population is, and how itwill grow. Many are interrelated.

1)Age structure2)Total fertility3)Relationships between the populationand the environment.4) Birth/Death rate, and related factorsThe purpose of demography is to predict.

Population Dynamics-the study of an individual population, andits relationship with other populations, aswell as its environment.

-is often applied to endangered species, and species that are harvested.

-especially in the case of harvested species,gives a picture of the sustainable rate ofharvest. (fish, trees, crabs, geese, etc…)

Equations for Population Change

P2 = P1 + (B – D) + (I – E) Where:P1 is the number of individuals at time 1P2 is the number of individuals at time 2B is the number of individuals born D is the number of individuals that diedI is the number of individuals that immigratedE is the number of individuals that emigrated

Ignoring I and E, the equation becomes: P2 = P1 + (B – D)

In other words, the growth rate of a population (g) is simply the differencebetween the birth and death rate.

Doubling Time: (T) the amount of time it takes for a population to double itssize.

Doubling time is estimated by the formula: T = 70/annual growth rate

Where T is the doubling time, and the annual growth rate is expressed as a percentage.

Ex: a population with a 1.7% annual growthwill double in about 42 years. (70/1.7)

Calculating Population Growth

Birth Rate: (b), is the number of births perunit time (B), divided by the total Population (N).

b = B/N

Death Rate: (d), is the number of deaths per unit time (D), divided by the total Population (N).

d = D/N

Growth Rate: The # of births minus the # of deaths per unit time divided by the totalpopulation. g = (B – D) /N

Ex: A total population of 18,700,000-261,800 births in 1 year-130,900 deaths in 1 year

Birth rate: 261,800/18, 700,000 = 1.4%

Death rate: 130,900/18,700,000 = 0.7%

Growth Rate:

(261800-130,900) / 18,700,000 = 0.7%

Crude Birth Rate: the number of births per 1000 individuals per year. Crude Death Rate: the number of deaths per 1000 individuals per year. Crude Growth Rate: the net number addedper 1000 individuals per year.

Total Fertility Rate:(TFR)average number of children born to a woman through her child-bearing years.

Future Human Population Growth

-The size of the future human populationdepends greatly on the amount of fertilityIncrease or decrease. -The population is currently following anexponential growth curve, (overall pop.)

-Populations generally follow a logisticalcurve, where a capacity is reached, andthe population numbers plateau.

Demographic TransitionAs a population matures, it goes through a characteristic set of steps.

A high death rate declines because of better sanitation and reduction in ACUTE diseases.

This followed by a reduction in the birth rate, and the population stabilizes at a lower number.

Causes of Change in Death Rates

Acute vs. Chronic Disease: acute disease(also called epidemic disease) appearsrapidly, spreads through the population,then disappears.It may reappear later in a further outbreakof the disease. Ex: flu, measles, cholera

Acute disease may affect a large portion of the population at once.

Chronic Disease is one that is always present in the population, but affects asmaller number of individuals overall. Ex; heart disease, cancer, stroke.Disease Types in Developed vs. Undeveloped Countries

Undeveloped countries are more susceptible to acute disease, while developed countries have more chronicdisease.

Population Age Structure-the proportion of the population ineach age class.-a population heavily weighted towardyouth will be rapidly growing-a population with a higher percentageof older people will be slow growingor declining.

Age structure gives insight into a populations history, and its future.

Population Momentum/Lag:Once a population has reached Replacement Level Fertility (the TFR required for the pop. to remain constant),the pop. will grow for several generations.

This is because many young women, notyet bearing children, are in the population.

When a population finally does stabilize, its size will be larger than the present size.

Studies suggest that the TFR decreases as income increases.

Ex: Bangladesh: TFR=4.3, annual income of a few hundred dollars/yearBrazil: TFR=2.9, annual income of $2000/year.