Editing Carrying capacity (section)

=== Planetary boundaries framework ===
According to its developers, the planetary boundaries framework defines “a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system.”<ref name=":4" /> Human civilization has evolved in the relative stability of the [[Holocene epoch]]; thus crossing planetary boundaries for safe levels of atmospheric carbon, ocean acidity, or one of the other stated boundaries could send the global ecosystem spiraling into novel conditions that are less hospitable to life—possibly reducing global human carrying capacity. 

This framework, developed in an article published in 2009 in ''[[Nature (journal)|Nature]]''<ref>{{Cite journal |last1=Rockström |first1=Johan |last2=Steffen |first2=Will |last3=Noone |first3=Kevin |last4=Persson |first4=Åsa |last5=Chapin |first5=F. Stuart III |last6=Lambin |first6=Eric |last7=Lenton |first7=Timothy M. |last8=Scheffer |first8=Marten |last9=Folke |first9=Carl |last10=Schellnhuber |first10=Hans Joachim |last11=Nykvist |first11=Björn |last12=de Wit |first12=Cynthia A. |last13=Hughes |first13=Terry |last14=van der Leeuw |first14=Sander |last15=Rodhe |first15=Henning |date=2009 |title=Planetary Boundaries: Exploring the Safe Operating Space for Humanity |url=http://dx.doi.org/10.5751/es-03180-140232 |journal=Ecology and Society |volume=14 |issue=2 |doi=10.5751/es-03180-140232 |issn=1708-3087|hdl=10535/5421 |s2cid=15182169 |hdl-access=free }}</ref> and then updated in two articles published in 2015 in ''Science''<ref name=":4" /> and in 2018 in ''PNAS'',<ref name=":5">{{Cite journal |last1=Steffen |first1=Will |last2=Rockström |first2=Johan |last3=Richardson |first3=Katherine |last4=Lenton |first4=Timothy M. |last5=Folke |first5=Carl |last6=Liverman |first6=Diana |last7=Summerhayes |first7=Colin P. |last8=Barnosky |first8=Anthony D. |last9=Cornell |first9=Sarah E. |last10=Crucifix |first10=Michel |last11=Donges |first11=Jonathan F. |last12=Fetzer |first12=Ingo |last13=Lade |first13=Steven J. |last14=Scheffer |first14=Marten |last15=Winkelmann |first15=Ricarda |date=2018 |title=Trajectories of the Earth System in the Anthropocene |journal=Proceedings of the National Academy of Sciences |language=en |volume=115 |issue=33 |pages=8252–8259 |doi=10.1073/pnas.1810141115 |issn=0027-8424 |pmc=6099852 |pmid=30082409 |doi-access=free |bibcode=2018PNAS..115.8252S }}</ref>  identifies nine stressors of planetary support systems that need to stay within critical limits to preserve stable and safe biospheric conditions (see figure below). Climate change and biodiversity loss are seen as especially crucial, since on their own, they could push the Earth system out of the Holocene state: “transitions between time periods in Earth history have often been delineated by substantial shifts in climate, the biosphere, or both.” <ref name=":4" />  
[[File:Estimates_of_how_the_different_control_variables_for_seven_of_nine_planetary_boundaries_have_changed_from_1950_to_present.png|thumb|Estimates of how the different control variables for seven of nine planetary boundaries have changed from 1950 to present. The green shaded polygon represents the safe operating space.]]
The scientific consensus is that humanity has exceeded three to five of the nine planetary boundaries for safe use of the biosphere and is pressing hard on several more.<ref name=":5" /> By itself, crossing one of the planetary boundaries does not prove humanity has exceeded Earth's human carrying capacity; perhaps technological improvements or clever management might reduce this stressor and bring us back within the biosphere's safe operating space. But when several boundaries are crossed, it becomes harder to argue that carrying capacity has not been breached.<ref>{{Cite journal |last=Higgs |first=Kerryn |date=2017 |title=Limits to growth: human economy and planetary boundaries |journal=[[The Journal of Population and Sustainability]] |volume=2 |issue=1 |doi=10.3197/jps.2017.2.1.15 |issn=2398-5496|doi-access=free }}</ref> 

Because fewer people helps reduce all nine planetary stressors, the more boundaries are crossed, the clearer it appears that reducing human numbers is part of what is needed to get back within a safe operating space.<ref>{{Cite book |last=Coole |first=Diana H. |title=Should we control world population ? |date=2018 |publisher=Polity press |isbn=978-1-5095-2340-5 |series=Political theory today |location=Cambridge, UK Medford, MA}}</ref><ref>{{Cite book |last=Conly |first=Sarah |url=http://dx.doi.org/10.1093/acprof:oso/9780190203436.001.0001 |title=One Child |date=2016 |publisher=Oxford University Press |doi=10.1093/acprof:oso/9780190203436.001.0001 |isbn=978-0-19-020343-6}}</ref> Population growth regularly tops the list of causes of humanity's increasing impact on the natural environment in Earth system science literature.<ref>{{Cite journal |last=Bourban |first=Michel |date=2019 |title=Croissance démographique et changement climatique: repenser nos politiques dans le cadre des limites planétaires |url=http://dx.doi.org/10.3917/lpe.003.0019 |journal=La Pensée écologique |volume=3 |issue=1 |pages=19–37 |doi=10.3917/lpe.003.0019 |s2cid=203184072 |issn=2558-1465}}</ref> Recently, planetary boundaries developer Will Steffen and co-authors ranked global population change as the leading indicator of the influence of socio-economic trends on the functioning of the Earth system in the modern era, post-1750.<ref>{{Cite journal |last1=Steffen |first1=Will |last2=Broadgate |first2=Wendy |last3=Deutsch |first3=Lisa |last4=Gaffney |first4=Owen |last5=Ludwig |first5=Cornelia |date=2015 |title=The trajectory of the Anthropocene: The Great Acceleration |url=http://dx.doi.org/10.1177/2053019614564785 |journal=The Anthropocene Review |volume=2 |issue=1 |pages=84 |doi=10.1177/2053019614564785 |bibcode=2015AntRv...2...81S |issn=2053-0196|hdl=1885/66463 |s2cid=131524600 |hdl-access=free }}</ref>