1) Population Size
2) Disease Incidence
3) Finite Resources
4) Animal Extinctions
5) Climate Change
1) Population Size
The human population has sky-rocketed within the past 3 centuries, increasing approximately ten-fold to >7 billion and is projected to reach 11 billion by 2100 (01). As seen below, even 300 years ago, it had never been higher (02). Every new human on our planet further divides its finite resources and increases our waste output. Eminent geneticist, Professor Steve Jones, has described how “humans are 10,000 times more common than we should be, according to the rules of the animal kingdom” (03).
Professor Frank Fenner, who was instrumental in the eradication of smallpox (the only disease ever to be eradicated) and a member of the Australian Academy of Science and the Royal Society, gave an interview voicing his concern for our species' future to The Australian, 16/06/2010: "Homo sapiens will become extinct, perhaps within 100 years... Mitigation would slow things down a bit, but there are too many people here already... As the population keeps growing to seven, eight or nine billion, there will be a lot more wars over food...We'll undergo the same fate as the people on Easter Island.
2) Disease Incidence
A large population drastically increases the rate of disease transmission for all communicable diseases (04). This holds true even for many non-communicable diseases, such as lung cancer or ischaemic heart disease (05).
The agricultural requirements of feeding a growing population elevate the risk of zoonotic infections, as livestock populations must also increase. Dr. Lonnie King, a director at the CDC, cites population growth as a "major consideration" among the factors "that are creating the conditions for a perfect microbial storm" (06). Separately, population growth is noted by the CDC as a cause of the global decrease in water quality, another potential source of disease (07). Similarly, outdoor air pollution alone “leads to 3.3 million premature deaths per year worldwide”, a figure that is expected to double by 2050 (08).
3) Finite Resources
The most widely recognised non-renewable resources are the fossil fuels, which account for >85% of global energy consumption, with 15-30% of this energy “used to simply supply food for 7.2 billion people" (09). However, we are rapidly exhausting many other finite resources too. Current groundwater usage is “unsustainable” (10) and there has been “a ten-fold increase in total water extraction in the last century”, with “stresses on water mainly driven by four interrelated processes: population growth; economic growth; increased demand for food, feed and energy; and increased climate variability" (11). Not only this but "the number of people vulnerable to flood disasters worldwide is expected to mushroom to two billion by 2050 as a result of climate change, deforestation, rising sea levels and population growth” (11).
Phosphate, a key ingredient in fertiliser, is predicted to “run out in 50 years”, though our need for it will be even greater then as population growth "will require food production to at least double by 2050" (12). This is despite the fact that about 1 in 10 people on the planet already are undernourished (13).
Furthermore, "antimicrobial effectiveness is a precious, limited resource. Antibiotics become less effective the more they are used” and even now, there is an “ongoing explosion of antibiotic-resistant infections” (14). We are progressively eliminating the only significant defence we have against pathogenic bacteria. A 2016 report commissioned by the UK Department of Health found that "at least 700,000 people die every year already from drug-resistant infections... by 2050, 10 million lives a year and a cumulative 100 trillion USD of economic output are at risk due to the rise of drug resistant infections. Even if we manage to reduce the unnecessary use of anti-microbials over the next decade, with a growing world population… the world will need a functioning R&D pipeline of new antimicrobials" (15).
4) Animal Extinctions
Excessive population growth selfishly causes the death and extinction of the other species who share the planet. Humans are the last to feel the effects and animals/plants the first because in almost any given situation where their needs are in competition with those of humans, humans' will take precedence. Animal homes, rather than human homes are bulldozed to make way for more humans and pollutants are pumped and dumped into animal habitats, not human houses.
Zoologists warn that “the number of species that have gone extinct in the last century would [normally] have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear”. The correlation between the human population explosion, starting c.1700 and the increasing rate of animal extinction is striking (16). For example, “rapidly expanding human populations” have caused gorillas and chimpanzees to be “pushed to the brink of extinction” (17).
Rogers et al. 2013, Marine Pollution Bulletin, 74(2), 491–494:
"The continued expansion in global population exerts ever increasing pressures on scarcer ocean resources through overexploitation and on marine ecosystems through indirect impacts such as pollution. It is therefore important to recognise that growing impacts on the ocean are inseparable from the population growth and per-capita resource use, and tackling these issues... has to be part of a wider re-evaluation of the core values of human society and its relationship to the natural world and the resources on which we all rely.""It is clear that human activities have led to intense multiple stressors acting together in many marine ecosystems. Most notably these are arising from overexploitation of biotic resources, climate change effects forming the so-called “deadly trio” (ocean warming, acidification and hypoxia/anoxia) and pollution. The “deadly trio” are... partially or entirely associated with the majority of the major extinction events in Earth’s past".
Ceballos et al. 2015, Science Advances, 1(5), e1400253, DOI: 10.1126/sciadv.1400253
"A sixth mass extinction is already under way... This affects human well-being by interfering with crucial ecosystem services such as crop pollination and water purification and by destroying humanity’s beautiful, fascinating, and culturally important living companions".
5) Climate Change
A 2009 study in The Lancet notes that “climate change is the biggest global health threat of the 21st century” (18). As with finite resource expenditure, climate change synergistically exacerbates disease transmission, particularly in the area of mosquito-borne pathogens. For example, by 2085, “about 5–6 billion people (50–60% of the projected global population) [will] be at risk of dengue transmission, compared with 3·5 billion people, or 35% of the population, if climate change did not happen" (19).
Anthropogenic climate change largely results from increased CO₂ emissions due to fossil fuel combustion (20). Procreation is a frequently overlooked contributor to CO₂ emissions; in the US for example, “each child adds about 9441 metric tons of carbon dioxide to the carbon legacy of an average female, which is 5.7 times her lifetime emissions” (21). In fact, "slowing population growth could provide 16–29% of the emissions reductions suggested to be necessary by 2050 to avoid dangerous climate change” and the benefits would be cumulative, such that by the end of the century, there could be reductions in “total emissions from fossil fuel use by 37–41%” (22). Carbon emissions over the next few decades will have irreversible consequences “for the next ten millennia and beyond” (23).
Animal populations oscillate between peaks and troughs over time, with the transition from peak to trough characterised by considerable suffering, in the form of famine, disease and predation. All indications are that the unchecked growth of the human population will elicit a concomitant level of suffering for humans. So far, our continuous population expansion has been enabled by sacrificing other species but we will eventually run out of them and have impoverished ourselves in the process.
Leading journals describe how “the inexorable demographic momentum of the global human population is rapidly eroding Earth’s life-support system” (24). Waste production and resource consumption would occur at roughly one thousandth of the current rate, were our population reduced a thousand fold. In contrast, there is almost no benefit to increasing our population.
(01) Gerland et al., 2014, World population stabilization unlikely this century. Science. 346(6206), 234-237.
(02) E.M. Murphy, 1989, World Population: Toward the Next Century. Population Reference Bureau.
(03) Prof. Steve Jones, 7/10/2008, University College London - Department of Genetics, Evolution and Environment. Human evolution is over, says UCL academic. UCL Lunch Hour Lecture.
(04) Arneberg et al., 1998, Host densities as determinants of abundance in parasite communities. Proceeds of the Royal Society B. 265(1403), 1283-1289.
(05) Chaix et al., 2006, Disentangling contextual effects on cause-specific mortality in a longitudinal 23-year follow-up study: impact of population density or socioeconomic environment? International Journal of Epidemiology. 35(3), 633-643.
(06) L. King, 2008, Collaboration in Public Health: A New Global Imperative. Public Health Reports. 123(3), 264–265.
(07) Centers for Disease Control and Prevention, 2012, Global Water, Sanitation, & Hygiene (WASH) Burden.
(08) J. Lelieveld et al., 2015, The contribution of outdoor air pollution sources to premature mortality on a global scale. Nature. 525(7569), 367–371.
(09) Schramski et al., 2015, Human domination of the biosphere: Rapid discharge of the earth-space battery foretells the future of humankind. PNAS. 112(31), 9511–9517.
(10) Famiglietti et al., 2015, Uncertainty in global groundwater storage estimates in a Total Groundwater Stress framework. Water Resources Research. 51(7), 5198–5216.
(11) UNESCO: The UN World Water Development Report 4, Volume 1, 2012. Managing Water under Uncertainty and Risk.
(12) Natasha Gilbert, 2009, Environment: The disappearing nutrient. Nature. 461, 716-718.
(13) Food and Agriculture Organisation of the United Nations, 2015, The State of Food Insecurity in the World. Meeting the 2015 international hunger targets: taking stock of uneven progress.
(14) Spellberg et al., 2008, The Epidemic of Antibiotic-Resistant Infections: A Call to Action for the Medical Community from the Infectious Diseases Society of America. Clinical Infectious Diseases. 46(2), 155-164.
(15) Jim O'Neill, 2016, Tackling Drug-Resistant Infections Globally: The Review on Antimicrobial Resistance. A report commission by the UK Department of Health.
(16) Ceballos et al., 2015, Accelerated modern human–induced species losses: Entering the sixth mass extinction. Science Advances. 1(5), e1400253.
(17) Walsh et al., 2003, Catastrophic ape decline in western equatorial Africa. Nature. 422(6932), 611-614.
(18) Costello et al., 2009, Managing the health effects of climate change. The Lancet. 373(9676), 1693–1733.
(19) Hales et al., 2002, Potential effect of population and climate changes on global distribution of dengue fever: an empirical model. The Lancet. 360(9336), 830–834.
(20) Read et al., 1994, What Do People Know About Global Climate Change? 2. Survey Studies of Educated Laypeople. Risk Analysis. 14(6), 971–982.
(21) Murtaugh & Schlax, 2009, Reproduction and the carbon legacies of individuals. Global Environmental Change. 19, 14–20.
(22) O'Neill et al., 2010, Global demographic trends and future carbon emissions. PNAS. 107(41), 17521–17526.
(23) Clark et al., 2016, Consequences of twenty-first-century policy for multi-millennial climate and sea-level change. Nature Climate Change. 6(4), 360–369.
(24) Bradshaw & Brook, 2014, Human population reduction is not a quick fix for environmental problems. PNAS. 111(46), 16610–16615.