24th Pacific Science Congress (PSC-24)

  Human-induced environmental changes are rapidly reshaping the Earth system, withsignificant implications for human habitability. While existing safe and just Earthsystem boundaries have delineated critical thresholds for various planetary processes,the future evolution of human habitable conditions remains unclear. Here we proposethe habitable composite volume (HCV),defined on a three- dimensionalenvironmental phase space P,to quantify the collapsing boundaries of humanhabitability under the Great Acceleration. The historical period (1981-2014demonstrates persistent HCV decline from 0.66 to 0.48. Under the projections of theShared Socioeconomic Pathways, HCV may decline by up to 78% by 2100, withcollapsing areas encompassing 91.6% of global land, drastically reducing viableliving space. Most alarmingly, high-risk regions-where collapse coincides with largepopulations -expand nearly tenfold (1.7% to 16-18%)under moderate-to-highemissions, extending from developing regions to all continents demanding immediateglobal action. These findings highlight the escalating risks to human habitability andunderscore the urgency of both mitigation and adaptation strategies to address this global crisis.

Earth system boundaries,habitable composite volume,Sustainable Development,climate change