7.5 Billion And Counting: How Many Humans Can The Earth Support?


Published:

Humans are the most populous large mammal on Earth today, and probably in all of geological history. This World Population Day, humans number in the vicinity of 7.5 to 7.6 billion individuals.

Can the Earth support this many people indefinitely? What will happen if we do nothing to manage future population growth and total resource use? These complex questions are ecological, political, ethical – and urgent. Simple mathematics shows why, shedding light on our species’ ecological footprint.

The Mathematics Of Population Growth

In an environment with unlimited natural resources, population size grows exponentially. One characteristic feature of exponential growth is the time 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 one penny on Jan. 1, 2019, two pennies on Feb. 1, four on March 1, and so forth, with the payment doubling each month. How long would his $100 billion fortune uphold the contract? Take a moment to ponder and guess.

After one year, or 12 payments, your total contract receipts come to US$40.95, equivalent to a night at the movies. After two years, $167,772.15 – substantial, but paltry to a billionaire. After three 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 one penny), breaks the bank.

Real Population Growth

For real populations, doubling time is not constant. Humans reached 1 billion around 1800, a doubling time of about 300 years; 2 billion in 1927, a doubling time of 127 years; and 4 billion in 1974, a doubling time of 47 years.

On the other hand, world numbers are projected to reach 8 billion around 2023, a doubling time of 49 years, and barring the unforeseen, expected to level off around 10 to 12 billion by 2100.

This anticipated leveling off signals a harsh biological reality: Human population is being curtailed by the Earth’s carrying capacity, the population at which premature death by starvation and disease balances the birth rate.

Ecological Implications

Humans are consuming and polluting resources – aquifers and ice caps, fertile soil, forests, fisheries and oceans – accumulated over geological time, tens of thousands of years or longer.

Wealthy countries consume out of proportion to their populations. As a fiscal analogy, we live as if our savings account balance were steady income.

According to the Worldwatch Institute, an environmental think tank, the Earth has 1.9 hectares of land per person for growing food and textiles for clothing, supplying wood and absorbing waste. The average American uses about 9.7 hectares.

These data alone suggest the Earth can support at most one-fifth of the present population, 1.5 billion people, at an American standard of living.

Water is vital. Biologically, an adult human needs less than 1 gallon of water daily. In 2010, the U.S. used 355 billion gallons of freshwater, over 1,000 gallons (4,000 liters) per person per day. Half was used to generate electricity, one-third for irrigation, and roughly one-tenth for household use: flushing toilets, washing clothes and dishes, and watering lawns.

If 7.5 billion people consumed water 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.

World Health Organization figures show 2.1 billion people lack ready access to safe drinking water, and 4.5 billion lack managed sanitation. Even in industrialized countries, water sources can be contaminated with pathogens, fertilizer and insecticide runoff, heavy metals and fracking effluent.

Freedom To Choose

Though the detailed future of the human species is impossible to predict, basic facts are certain. Water and food are immediate human necessities. Doubling food production would defer the problems of present-day birth rates by at most a few decades. The Earth supports industrialized standards of living only because we are drawing down the “savings account” of non-renewable resources, including fertile topsoil, drinkable water, forests, fisheries and petroleum.

The drive to reproduce is among the strongest desires, both for couples and for societies. How will humans reshape one of our most cherished expectations – “Be fruitful and multiply” – in the span of one generation? What will happen if present-day birth rates continue?

Population stays constant when couples have about two children who survive to reproductive age. In some parts of the developing world today, couples average three to six children.

We cannot wish natural resources into existence. Couples, however, have the freedom to choose how many children to have. Improvements in women’s rights, education and self-determination generally lead to lower birth rates.

As a mathematician, I believe reducing birth 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.

Andrew D. Hwang is an associate professor of mathematics at College of the Holy Cross. His formal training is in differential geometry, the use of calculus to study curvature of space. Avocationally, he is interested in complex systems and emergent behavior from culture to consciousness, and in conveying the beauty and power of mathematical thought to non-mathematicians.

This article was originally published on The Conversation.

See also:
Tiny Houses Alone Can’t Solve The Housing Crisis. But Here’s What Can
Is Climate Change Driving You To Despair? Read This.

The Conversation

Edit Module
Edit ModuleShow Tags
Edit Module Edit ModuleShow Tags

Daily Astrology

December 13, 2019

A fascinating early morning dream can be a potent motivator. If destiny or a newly discovered sense of purpose appeals to you, go for it! Venus’ late morning conjunction with Pluto signals profits for some investors. Other souls encounter big dramas in…
Edit ModuleShow Tags

Alternative Health Directory

Browse all listings »

Edit ModuleShow Tags
Edit ModuleShow Tags

Calendar

December 2019

Come shine with us! Join us in harmony and in our goal to bring the light of Spiritualism forward to all those who are searching.

Where:
VFW Post 2597
775 Boston Rd, Rt 3A
Billerica, MA
View map »


Sponsor: The Spiritualist Fellowship Church Of New England
Website »

More information

A beautiful collection of messages from Jeshua Ben Joseph (Jesus) that will transform your life, as it did his. Coming together to study these teachings, to ponder, to savor, to deepen our...

Cost: $25 per class

Where:
Heart and Soul Holistic Healing Center
130 Massapoag Avenue
Sharon, MA  02067
View map »


Sponsor: Heart and Soul Holistic
Telephone: 781-258-9942
Contact Name: Barbara Ann Strassman
Website »

More information

Show More...
Show Less...

2nd and 4th Monday of every month This psychic message circle is for anyone wishing to raise their connection using their psychic centers known as the “clairs.” Learn how to use...

Cost: $20

Where:
Messages From Heaven Healing and Learning Center
646 Central Street
Suite 3
Leominster, MA
View map »


Website »

More information

Show More...
Show Less...

Show More...
Show Less...

What is a vigorous yoga practice, and who can benefit from it? With Marissa McAleer and Julie Rost This workshop will explore a more physical practice of yoga and how it can be used to...

Cost: $45

Where:
YogaLife Institute of NH
6 Chestnut Street
Lower Level
Exeter, NH  03833
View map »


Sponsor: YogaLife Institute of NH
Contact Name: Alice Bentley
Website »

More information

The Wellness Roundtable Holistic Practitioners Network creates an environment for wellness practitioners to inspire, educate and support one another, while building community and encouraging...

Cost: $20 (Drop-ins are welcome)

Where:
Sohum Yoga and Meditation Studio
30 Lyman St
#108B
Westborough, MA
View map »


Sponsor: 01581
Telephone: 508-329-3338
Contact Name: Ritu Kapur
Website »

More information

How would it feel to have direct education on changing your feelings so you do start to ask for what you truly want? Each month, come and practice hands-on skills to get into the habit of...

Cost: $15

Where:
Awaken Holistic Counseling Services
2 Liberty St., Unit 2L
Newburyport, MA  01950
View map »


Sponsor: Awaken Holistic Counseling Services, LLC
Telephone: 978-255-7893
Contact Name: Kerri Morrison
Website »

More information

Show More...
Show Less...

The nights of December fall dark and early. Homes are filled with warm firelight and flickering candle glow. As the year draws to a close, pause under the peaceful light of December’s Full...

Cost: $10–15 suggested donation

Where:
A Touch of Magick
195 S Main Street
Uxbridge, MA
View map »


Telephone: (508) 779-7386
Website »

More information

Sound baths provide an opportunity to relax and journey into a healing, meditative and rejuvenating state. There is nothing you need to do, know or believe. Join us for a powerful, yet casual...

Cost: $25

Where:
Moth & Moon Studio
173 South River Rd
Suite #4
Bedford, NH  03110
View map »


Sponsor: Jeffrey Charles Warren
Contact Name: Jeffrey Warren
Website »

More information

Show More...
Show Less...

Multi-skilled, and varied holistic practitioner group in Lincoln Area / Metro-West Boston welcomes new practitioner-members. Open invitation to any local practitioner, teacher, researcher,...

Cost: Free, or $5-$15

Where:
Member-homes/offices
Lincoln, MA  01773-4107


Sponsor: Lincoln Area Wellness Collaborative
Telephone: 781-738-1920
Contact Name: Jai Kaur

More information

Show More...
Show Less...

This is a class that will teach you how to make your own wire-wrapped gemstone pendant! Don’t be discouraged—it is simpler than you think, and you’ll have great fun in crafting...

Cost: $40 per person or $35 more than one, includes supplies

Where:
The Healing Power of Flowers — Heaven and Earth
68 Stiles Rd, Unit A
Salem, NH  03079
View map »


Sponsor: The Healing Power of Flowers - Heaven and Earth
Telephone: 603-275-7688
Contact Name: Stacey
Website »

More information

Learn to overcome spinal tensions through therapeutic postures, designed to decompress your spine and relieve pain. Taught by a certified yoga therapist, classes bring you through poses...

Cost: 5/$50

Where:
Bliss Through Yoga
484 Bedford St
East Bridgewater, MA  02333
View map »


Telephone: 508-331-3564
Contact Name: Janice O'Brien
Website »

More information

Show More...
Show Less...
Edit ModuleShow Tags
Edit Module Edit ModuleShow Tags