How Long Did It Take for the Population to Double Once Again
Humans are the near populous big mammal on Earth today, and probably in all of geological history. This Globe Population Day, humans number in the vicinity of 7.5 to seven.half-dozen billion individuals.
Can the Earth support this many people indefinitely? What volition happen if we practise nothing to manage future population growth and total resource use? These complex questions are ecological, political, upstanding – and urgent. Elementary mathematics shows why, shedding light on our species' ecological footprint.
The mathematics of population growth
In an environs with unlimited natural resources, population size grows exponentially. One characteristic feature of exponential growth is the fourth dimension a population takes to double in size.
Exponential growth tends to start slowly, sneaking up before ballooning in just a few doublings.
To illustrate, suppose Jeff Bezos agreed to give you 1 penny on Jan. 1, 2019, two pennies on Feb. i, iv on March ane, and then forth, with the payment doubling each calendar month. How long would his $100 billion fortune uphold the contract? Take a moment to ponder and approximate.
After one year, or 12 payments, your total contract receipts come to U.s.a.$forty.95, equivalent to a night at the movies. After two years, $167,772.fifteen – substantial, only paltry to a billionaire. Afterward 3 years, $687,194,767.35, or about one week of Bezos' 2017 income.
The 43rd payment, on July 1, 2022, just short of $88 billion and equal to all the preceding payments together (plus ane penny), breaks the depository financial institution.
Real population growth
For real populations, doubling time is not constant. Humans reached 1 billion around 1800, a doubling time of almost 300 years; 2 billion in 1927, a doubling time of 127 years; and four billion in 1974, a doubling time of 47 years.
On the other manus, world numbers are projected to achieve 8 billion around 2023, a doubling time of 49 years, and barring the unforeseen, expected to level off around ten to 12 billion by 2100.
This anticipated leveling off signals a harsh biological reality: Human population is existence curtailed by the Earth's conveying capacity, the population at which premature death by starvation and affliction balances the nativity rate.
Ecological implications
Humans are consuming and polluting resources – aquifers and water ice caps, fertile soil, forests, fisheries and oceans – accumulated over geological time, tens of thousands of years or longer.
Wealthy countries swallow out of proportion to their populations. As a fiscal analogy, we live every bit if our savings account residual were steady income.
Co-ordinate to the Worldwatch Institute, an environmental call up tank, the Earth has 1.ix hectares of country per person for growing food and textiles for clothing, supplying wood and absorbing waste. The average American uses near nine.seven hectares.
These data lonely suggest the Earth can support at most ane-5th of the present population, 1.five billion people, at an American standard of living.
H2o is vital. Biologically, an adult man needs less than i gallon of water daily. In 2010, the U.Due south. used 355 billion gallons of freshwater, over 1,000 gallons (4,000 liters) per person per twenty-four hours. Half was used to generate electricity, 1-third for irrigation, and roughly one-tenth for household use: flushing toilets, washing dress and dishes, and watering lawns.
If 7.5 billion people consumed h2o at American levels, world usage would top 10,000 cubic kilometers per year. Total world supply – freshwater lakes and rivers – is about 91,000 cubic kilometers.
Globe Wellness Organization figures show 2.i billion people lack gear up admission to safety drinking water, and 4.5 billion lack managed sanitation. Even in industrialized countries, water sources can exist contaminated with pathogens, fertilizer and insecticide runoff, heavy metals and fracking effluent.
Freedom to choose
Though the detailed future of the human species is incommunicable to predict, basic facts are certain. Water and food are immediate human necessities. Doubling food production would defer the problems of nowadays-twenty-four hours birth rates by at well-nigh a few decades. The Earth supports industrialized standards of living just considering we are drawing downward the "savings business relationship" of non-renewable resource, including fertile topsoil, potable water, forests, fisheries and petroleum.
The drive to reproduce is among the strongest desires, both for couples and for societies. How will humans reshape ane of our most cherished expectations – "Exist fruitful and multiply" – in the span of 1 generation? What will happen if nowadays-day birth rates continue?
Population stays constant when couples accept well-nigh two children who survive to reproductive historic period. In some parts of the developing world today, couples average three to six children.
We cannot wish natural resources into being. Couples, still, accept the freedom to choose how many children to have. Improvements in women's rights, education and cocky-determination generally lead to lower birth rates.
As a mathematician, I believe reducing nativity rates substantially is our best prospect for raising global standards of living. As a citizen, I believe nudging human behavior, by encouraging smaller families, is our most humane hope.
Source: https://theconversation.com/7-5-billion-and-counting-how-many-humans-can-the-earth-support-98797
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