Nonlinear Relationships of Carbon Emissions with Global Mortality: Trends, Projections, and Health Equity

Increased greenhouse gas (GHG) emissions usually indicate better economic development and improved healthcare but could also accelerate environmental degradation and elevate mortality. To study this sustainability paradox, we evaluated associations between per capita GHG emissions and mortality across 76 major countries from 1990 to 2019 and projected future trends. GHG emissions and mortality data were from the Global Carbon Project and Global Burden of Disease 2021, respectively. We identified an N-shaped nonlinear association with inflection points at five and 15 tons per capita. Mortality initially decreased with rising emissions when below five tons per capita with reductions in communicable diseases, then increased by 15 tons per capita with increments in noncommunicable diseases, and eventually slightly declined beyond 15 tons. Health inequality worsened, with the concentration index falling from -0.812 (1990) to -0.882 (2019), indicating longer life expectancies in low emitters. Males and older adults faced a higher climate-related mortality risk, including cardiovascular death and extreme temperature-related injuries. Projections under a low-emission scenario indicated greater mortality reductions for low- and middle-income countries from 2025 to 2040, whereas high-income countries were expected to meet complex trade-offs. Our findings highlight the urgent need for context-specific decarbonization and climate justice policies to achieve the UN Sustainable Development Goals.