Anthropogenic climate change drives rising global heat stress and its spatial inequality.

Global heat stress is intensifying under climate change, yet the relative roles of natural and anthropogenic forcing remain insufficiently quantified. Here, we show that global heat stress trend, assessed with the Universal Thermal Climate Index, increases markedly over the past four decades, with 52% of land area experiencing rises in mean heat stress intensity and 67% showing increases in extreme heat stress days. We find that anthropogenic climate change overwhelmingly dominates these trends, with the land area it dominates nearly twice as large as that dominated by natural climate change. Anthropogenic climate change also results in pronounced spatial inequality in heat stress trends across different economies, with low-income economies experiencing a growth rate two to three times higher than that of high-income economies. These findings demonstrate that human-induced climate change is amplifying global heat stress while deepening existing spatial inequalities, underscoring the urgency of equitable climate change adaptation.