A Mounting Health Toll

Heat caused some 710,000 deaths worldwide in 2023, a record level. For the first time, more than seven in ten are attributable to human-caused climate change. The Lancet Countdown report, produced with the WHO and led by University College London, draws on 54 indicators. It finds that heat-related deaths rose by nearly 36% in the years following the 2015 Paris Agreement, compared with the previous decade.

A Widening Economic and Health Cost

The impact is not limited to mortality. In 2025, heat exposure cost 573 billion potential working hours, equivalent to $1.07 trillion in lost income. Drought affected 51.8% of land surfaces for at least one month. Warming also expands the terrain for disease: between 1981-1990 and 2016-2025, conditions favorable to dengue transmission rose 24% for the Aedes albopictus mosquito and 7% for Aedes aegypti.

The Mechanism: Fossil Projects That Extend the Trajectory

The causal chain is direct. More fossil fuels extracted and burned means more emissions and heat, hence more mortality, lost work and health risks. Yet the strategies of major producers do not break with this logic. The top 100 oil and gas companies plan to produce, by 2040, 150% more fossil fuels than the level compatible with 1.5°C. The gap stood at 138% a year earlier: it is widening.

Benefits Already Measurable

The same report shows that reducing fossil pollution is paying off. In 70 countries, improved air quality prevents roughly 323,000 deaths a year. Global investment in clean energy hit a record $2.1 trillion, and sector jobs grew 2.3% in 2024, approaching double the direct jobs tied to fossil fuels.

Solar illustrates the shift in scale: it overtook nuclear in global electricity generation in 2025, with 13% more energy, after panel prices fell 90% since 2010. On adaptation, about one country in four has a national climate-health plan, versus 14 WHO member states in 2015.

Limits and Inequalities

These figures warrant caution. The 2023 deaths and the 2025 work losses do not cover the same year. Deaths avoided through cleaner air are estimates. Above all, adaptation remains uneven: in 2025, rich countries accounted for 55% of laws linking climate and health, versus 2% for developing countries. Available data do not allow measurement of the future effect of these dynamics.

What to Conclude

Inaction carries a quantified human and economic cost, and it is rising. The benefits of reducing fossil pollution and deploying clean energy are already visible, but they coexist with fossil production plans that drift away from 1.5°C. Ahead of COP31 in Antalya, the authors call for climate change to be recognized as a global health emergency.

This article was written with the assistance of artificial intelligence and verified by our editorial team.