Editing Carrying capacity (section)

== Humans ==

Human carrying capacity is a function of how people live and the technology at their disposal. The two great economic revolutions that marked human history up to 1900—the agricultural and industrial revolutions—greatly increased the Earth's human carrying capacity, allowing human population to grow from 5 to 10 million people in 10,000 BCE to 1.5 billion in 1900.<ref>{{Cite web   |title=Historical Estimates of World Population |url=https://www.census.gov/data/tables/time-series/demo/international-programs/historical-est-worldpop.html |access-date= |website=Census.gov}}</ref> The immense technological improvements of the past 100 years—in applied chemistry, physics, computing, genetic engineering, and more—have further increased Earth's human carrying capacity, at least in the short term. Without the Haber-Bosch process for fixing nitrogen, modern agriculture could not support 8 billion people.<ref>{{Cite journal |last=Smil |first=Vaclav |date=1999 |title=Detonator of the population explosion |journal=Nature |language=en |volume=400 |issue=6743 |pages=415 |doi=10.1038/22672 |bibcode=1999Natur.400..415S |s2cid=4301828 |issn=0028-0836|doi-access=free }}</ref> Without the Green Revolution of the 1950s and 60s, famine might have culled large numbers of people in poorer countries during the last three decades of the twentieth century.<ref>{{Cite journal |last1=Gollin |first1=Douglas |last2=Hansen |first2=Casper Worm |last3=Wingender |first3=Asger Mose |date=2021 |title=Two Blades of Grass: The Impact of the Green Revolution |url=https://www.journals.uchicago.edu/doi/10.1086/714444 |journal=Journal of Political Economy |language=en |volume=129 |issue=8 |pages=2344–2384 |doi=10.1086/714444 |s2cid=53401811 |issn=0022-3808}}</ref>

Recent technological successes, however, have come at grave environmental costs. [[Climate change]], ocean acidification, and the huge dead zones at the mouths of many of world's great rivers, are a function of the scale of contemporary agriculture<ref name="Crist-2017">{{Cite journal |last1=Crist |first1=Eileen |last2=Mora |first2=Camilo |last3=Engelman |first3=Robert |date=2017-04-21 |title=The interaction of human population, food production, and biodiversity protection |url=http://dx.doi.org/10.1126/science.aal2011 |journal=Science |volume=356 |issue=6335 |pages=260–264 |doi=10.1126/science.aal2011 |pmid=28428391 |bibcode=2017Sci...356..260C |s2cid=12770178 |issn=0036-8075|url-access=subscription }}</ref> and the many other demands 8 billion people make on the planet.<ref>{{Cite journal |last1=Ripple |first1=William J. |last2=Wolf |first2=Christopher |last3=Newsome |first3=Thomas M. |last4=Galetti |first4=Mauro |last5=Alamgir |first5=Mohammed |last6=Crist |first6=Eileen |last7=Mahmoud |first7=Mahmoud I. |last8=Laurance |first8=William F. |date=2017-11-13 |title=World Scientists' Warning to Humanity: A Second Notice |url=http://dx.doi.org/10.1093/biosci/bix125 |journal=BioScience |volume=67 |issue=12 |pages=1026–1028 |doi=10.1093/biosci/bix125 |issn=0006-3568|hdl=11336/71342 |hdl-access=free }}</ref> Scientists now speak of humanity exceeding or threatening to exceed 9 planetary boundaries for safe use of the biosphere.<ref name=":4">{{Cite journal |last1=Steffen |first1=Will |last2=Richardson |first2=Katherine |last3=Rockström |first3=Johan |last4=Cornell |first4=Sarah E. |last5=Fetzer |first5=Ingo |last6=Bennett |first6=Elena M. |last7=Biggs |first7=Reinette |last8=Carpenter |first8=Stephen R. |last9=de Vries |first9=Wim |last10=de Wit |first10=Cynthia A. |last11=Folke |first11=Carl |last12=Gerten |first12=Dieter |last13=Heinke |first13=Jens |last14=Mace |first14=Georgina M. |last15=Persson |first15=Linn M. |date=2015-02-13 |title=Planetary boundaries: Guiding human development on a changing planet |url=http://dx.doi.org/10.1126/science.1259855 |journal=Science |volume=347 |issue=6223 |doi=10.1126/science.1259855 |pmid=25592418 |hdl=1885/13126 |s2cid=206561765 |issn=0036-8075|hdl-access=free }}</ref> Humanity's unprecedented ecological impacts threaten to degrade the [[ecosystem service]]s that people and the rest of life depend on—potentially decreasing Earth's human carrying capacity.<ref name="MEA-2005">{{Cite book |last=(Program) |first=Millennium Ecosystem Assessment |url=http://worldcat.org/oclc/1264940723 |title=Ecosystems and human well-being : synthesis |date=2005 |publisher=Island Press |isbn=1-59726-039-8 |oclc=1264940723}}</ref> The signs that we have crossed this threshold are increasing.<ref>IPCC, 2014: Summary for Policymakers. In: ''Climate Change 2014: Mitigation of Climate Change. Contribution of Work- ing Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change'' [Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.</ref><ref name="IPBES-2019">IPBES. (2019). ''Summary for policymakers. Global assessment report on biodiversity and ecosystem services.'' Intergovernmental Panel on Biodiversity and Ecosystem Services Secretariat.</ref>  

The fact that degrading Earth's essential services is obviously possible, and happening in some cases, suggests that 8 billion people may be above Earth's human carrying capacity. But human carrying capacity is always a function of a certain number of people living a certain way.<ref name="Pimentel-1994">{{Cite journal |last1=Pimentel |first1=David |last2=Harman |first2=Rebecca |last3=Pacenza |first3=Matthew |last4=Pecarsky |first4=Jason |last5=Pimentel |first5=Marcia |date=1994 |title=Natural resources and an optimum human population |url=http://link.springer.com/10.1007/BF02208317 |journal=Population and Environment |language=en |volume=15 |issue=5 |page=348 |doi=10.1007/BF02208317 |bibcode=1994PopEn..15..347P |s2cid=153634463 |issn=0199-0039|url-access=subscription }}</ref><ref name="Dasgupta-2019">{{Cite book |last=S. |first=Dasgupta, Partha |url=http://worldcat.org/oclc/1097199008 |title=Time and the generations : population ethics for a diminishing planet |year=2019 |publisher=Columbia University Press |isbn=978-0-231-16012-4 |oclc=1097199008}}</ref> This was encapsulated by Paul Ehrlich and James Holdren's (1972) IPAT equation: environmental impact (I) = population (P) x affluence (A) x the technologies used to accommodate human demands (T).<ref>P.R. Ehrlich and J.P. Holdren. One-dimensional ecology. ''Bulletin of the Atomic Scientists'', May 1972: 16-27</ref> IPAT has found spectacular confirmation in recent decades within climate science, where the Kaya identity for explaining changes in {{CO2}} emissions is essentially IPAT with two technology factors broken out for ease of use.<ref>{{Cite book |url=https://www.worldcat.org/oclc/45731212 |title=Environment, energy, and economy : strategies for sustainability |date=1997 |publisher=United Nations University Press |others=Yōichi Kaya, Keiichi Yokobori, Energy, and Economic Development" Tokyo Conference on "Global Environment |isbn=0-585-22996-1 |location=Tokyo |oclc=45731212}}</ref>

This suggests to technological optimists that new technological discoveries (or the deployment of existing ones) could continue to increase Earth's human carrying capacity, as it has in the past.<ref>{{Cite book |last=Simon |first=Julian Lincoln |url=https://www.worldcat.org/oclc/7177304 |title=The ultimate resource |date=1981 |publisher=Princeton University Press |isbn=0-691-09389-X |location=Princeton, N.J. |oclc=7177304}}</ref> Yet technology has unexpected side effects, as we have seen with stratospheric ozone depletion, excessive nitrogen deposition in the world's rivers and bays, and global climate change.<ref name="MEA-2005" /><ref name="Bradshaw-2021" /> This suggests that 8 billion people may be sustainable for a few generations, but not over the long term, and the term ‘carrying capacity’ implies a population that is sustainable indefinitely. It is possible, too, that efforts to anticipate and manage the impacts of powerful new technologies, or to divide up the efforts needed to keep global ecological impacts within sustainable bounds among more than 200 nations all pursuing their own self-interest, may prove too complicated to achieve over the long haul.<ref>{{Cite book |last=Mark. |first=Gardiner, Stephen |url=http://worldcat.org/oclc/753470941 |title=A perfect moral storm : understanding the ethical tragedy of climate change |date=2011 |publisher=Oxford University Press |isbn=978-0-19-537944-0 |oclc=753470941}}</ref>

One issue with applying carrying capacity to any species is that ecosystems are not constant and change over time, therefore changing the resources available. Research has shown that sometimes the presence of human populations can increase local [[biodiversity]], demonstrating that human habitation does not always lead to deforestation and decreased biodiversity. 

Another issue to consider when applying carrying capacity, especially to humans, is that measuring food resources is arbitrary. This is due to choosing what to consider (e.g., whether or not to include plants that are not available every year), how to classify what is considered (e.g., classifying [[edible plant]]s that are not usually eaten as food resources or not), and determining if [[Calorie|caloric values]] or [[Nutritional value|nutritional values]] are privileged. Additional layers to this for humans are their cultural differences in culinary preferences (e.g., some consume [[termites|flying termites]]) and individual choices on what to invest their labor into (e.g., fishing vs. farming), both of which vary over time. This leads to the need to determine whether or not to include all food resources or only those the population considered will actually consume. 

Measuring water resources carrying capacity is likewise highly arbitrary: choices in temporal resolution (e.g., monthly versus annual), spatial resolution (e.g., how subbasins are delineated), and whether to include human activities such as inter-basin water transfers and reservoir storage in the assessment can all lead to vastly different WRCC results.<ref>{{Cite journal |last=Wu |first=Zeqiang |last2=Fan |first2=Yifan |last3=Zhang |first3=Sheng |last4=Qian |first4=Xin |last5=Wang |first5=Guoqiang |date=2025-01-01 |title=Dynamic assessment of water resources carrying capacity under human impacts on the water cycle: A finer perspective at the spatiotemporal scale of basin |url=https://www.sciencedirect.com/science/article/abs/pii/S0959652624040514 |journal=Journal of Cleaner Production |volume=486 |pages=144602 |doi=10.1016/j.jclepro.2024.144602 |issn=0959-6526|url-access=subscription }}</ref> 

Carrying capacity measurements over large areas also assumes [[Homogeneity and heterogeneity|homogeneity]] in the resources available but this does not account for how resources and access to them can greatly vary within regions and populations. They also assume that the populations in the region only rely on that region’s resources even though humans exchange resources with others from other regions and there are few, if any, isolated populations. Variations in [[Standard of living|standards of living]] which directly impact resource consumption are also not taken into account. These issues show that while there are limits to resources, a more complex model of how humans interact with their ecosystem needs to be used to understand them.<ref>{{Cite journal |last=Cliggett |first=Lisa |date=2001 |title=Carrying Capacity's New Guise: Folk Models for Public Debate and Longitudinal Study of Environmental Change |url=http://dx.doi.org/10.1353/at.2001.0003 |journal=Africa Today |volume=48 |issue=1 |pages=3–19 |doi=10.1353/at.2001.0003 |issn=1527-1978|url-access=subscription }}</ref>