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

The planetary boundaries framework, introduced by Rockström and colleagues, identifies nine critical Earth system processes that regulate the stability of the planet [–]. Among these, climate change represents one of the most severely transgressed boundaries, with atmospheric CO₂ concentrations reaching 423 ppm in 2025—far exceeding the proposed safe operating space of 350 ppm [,]. The Paris Agreement established global commitments to limit warming to “well below 2°C” above pre-industrial levels, with aspirational efforts toward 1.5°C. However, recent evidence indicates that 2024 became the first calendar year to surpass the 1.5°C threshold, with global temperatures reaching 1.34–1.41°C above pre-industrial levels []. Current projections suggest an 86% probability that at least one year between 2025–2029 will exceed 1.5°C warming, with a 70% chance that the five-year average will surpass this threshold []. The 20-year retrospective average, which formally defines Paris Agreement compliance, indicates we may have already entered a sustained period above 1.5°C warming. Without substantial mitigation efforts, trajectories point toward 2.0°C warming by the late 2020s or early 2030s, and potentially 2.5–3.0°C by mid-century under high-emission scenarios []. The World Health Organization has declared climate change “humankind’s single biggest health threat,” with an estimated 3.6 billion people currently living in areas highly susceptible to climate impacts [,]. The mechanisms through which climate change affects health are multifaceted and synergistic, operating through both direct pathways (heat exposure, extreme weather events) and indirect pathways (food insecurity, vector-borne disease expansion, mental health deterioration, healthcare system disruption) [,]. Recent data from the Global Burden of Disease (GBD) Study 2021 reveals that global DALYs increased from 2.63 billion in 2010 to 2.88 billion in 2021, with COVID-19 emerging as the leading cause globally []. However, the climate-attributable portion of disease burden remains inadequately quantified, particularly across different warming thresholds. In 2019, high temperature exposure alone accounted for 11.7 million DALYs globally, with cardiovascular diseases representing the primary contributor []. Climate change disproportionately impacts vulnerable populations who contribute minimally to global emissions but face the harshest health consequences []. In vulnerable regions, death rates from extreme weather events are 15 times higher than in less vulnerable areas. Low- and middle-income countries (LMICs), which produce only 14% of global CO₂ emissions, face the greatest climate-related health risks due to limited adaptive capacity, weaker health systems, and higher baseline disease burdens []. Specific vulnerable groups include children under 5 years (681 million globally), elderly populations ≥65 years (727 million), women of reproductive age (1.89 billion), Indigenous peoples (476 million), and low-income communities (3.6 billion). These populations experience heightened vulnerability due to physiological susceptibility, socioeconomic constraints, geographic exposure, institutional barriers, and limited access to health services [,].