Beyond the 1.5°C planetary boundary: AI-forecast of Global Disease Burden and Health inequities.

BACKGROUND: The planetary boundary for climate change-initially set at global mean temperature increase of 1.5°C above pre-industrial levels-has been significantly transgressed. Understanding the mechanistic pathways through which climate warming impacts disease burden is critical for evidence-based policy interventions. OBJECTIVE: This study aims to quantify and explain the global burden of disease when planetary climate boundaries are crossed at 1.5°C, 2.0°C, and 2.5°C warming thresholds. METHODS: We applied a dual-phase framework: (1) Exploratory AI using Random Forest and XGBoost algorithms to identify non-linear relationships and threshold effects between temperature increase and disease burden; (2) Explanatory AI employing SHAP (SHapley Additive exPlanations) values and causal inference models to mechanistically explain pathways linking climate change to health outcomes. RESULTS: At 1.5°C warming, global heat-related deaths increase from baseline (2019) of 0.21 million to 0.35 million (+66.7%), with corresponding heat-related disability-adjusted life-years (DALYs) rising from 4.77 million to 8.20 million (+71.9%). Cardiovascular disease burden escalates from 24.18 million DALYs to 29.50 million (+22.0%). At 2.0°C warming, these impacts intensify dramatically: heat-related deaths reach 0.52 million (+147.6%) and DALYs 12.50 million (+162.1%), while CVD DALYs increase to 35.80 million (+48.1%). At 2.5°C warming, heat-related deaths surge to 0.78 million (+271.4%) with DALYs of 18.90 million (+296.4%), and CVD DALYs reach 44.20 million (+82.8%). CONCLUSIONS: Crossing planetary climate boundaries triggers exponential escalation of global disease burden through multiple, synergistic pathways disproportionately affecting vulnerable populations in low-resource settings. Urgent climate mitigation to limit warming below 2.0°C could prevent millions of premature deaths and substantial DALY losses globally. Health system adaptation strategies must prioritize vulnerable populations and integrate climate resilience into health policy frameworks.