More than warming: Climate change as an emerging health crisis

Climate change is already reshaping the environmental and social systems that sustain health.The 2025 Lancet Countdown shows that beyond rising temperatures, climate change is distorting water availability, weakening food security, degrading air quality, expanding infectious disease risks, and straining health systems. 1 These indirect and interconnected impacts increasingly drive the greatest health burden.Heat should therefore be reviewed not as the primary crisis, but as a warning signal of broader systemic disruption.We first examine heat as the most visible marker of climate risk, then show how cascading impacts on water, food, disease ecology, and health system resilience together constitute a deeper and more enduring threat to health, as summarized conceptually in Figure 1. RECORD HEAT IS VISIBLE, THE BROADER HEALTH CRISIS IS NOTHeat-related health risks have risen sharply.Eighty-four percent of recent heatwave days in 2020-2024 would not have occurred without climate change, and heat-related mortality in 2012-2021 is 63.2% higher than in 1990-1999.The mortality burden also remains unevenly distributed across regions, pronounced in Southern and Eastern Europe. 2 Heat exposure also reduces productivity, disrupts sleep and cognition, and strains cardiovascular and renal systems.In 2024, heat exposure caused 640 billion hours of lost labor productivity and nearly $1.1 trillion in economic losses. 1 The Global Burden of Disease 2023 study further indicates that 1.75 million deaths globally are attributable to non-optimal temperatures, including low temperatures and cold waves.Yet heat is only the most apparent signal of climate change.Focusing on temperature alone hides broader disruptions to water, food, disease dynamics, and health system stability.As illustrated in Figure 1, heat sits upstream of a broader set of interconnected pathways that operate through hydroclimatic extremes, food systems, infectious disease dynamics, and health systems. BEYOND HEAT: HYDROCLIMATIC EXTREMES AND THE HEALTH RISKS WE OVERLOOKChanges in hydrological systems may ultimately prove more damaging to health than heat alone.These risks often remain overlooked because their effects unfold gradually through indirect pathways, and are poorly captured in routine disaster monitoring.In 2015-2024, extreme precipitation increased across 64% of the world's land surface from 1961-1990, while 61% experienced extreme drought in 2024, nearly three times the extent seen in the 1950s.Disruptions to water supply, housing, health services, and food production increasingly shape population health.