Climate change is already inflicting a massive toll on global health, a new report warns. The 2025 assessment paints a bleak picture of record-breaking threats from heat, extreme weather, and wildfire smoke, indicating that the world is facing a crisis driven by a persistent reliance on fossil fuels.
2024 was the hottest year on record, with the average person exposed to an additional 16 health-threatening hot days directly caused by climate change. Vulnerable populations faced even higher risks, with children under one and adults over 65 experiencing an average of 20 heatwave days each, marking increases of 389% and 304% respectively compared to the 1986–2005 baseline.
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Heat-related mortality has also risen significantly. Between 2012 and 2021, an average of 546,000 people died annually from heat exposure. Drier conditions have fueled more intense wildfires, resulting in a record 154,000 deaths in 2024 due to fine particle pollution (PM2.5) from smoke, a 36% increase over the previous decade’s average.
Food insecurity has worsened alongside these climate extremes. Droughts and heatwaves pushed 123 million more people into moderate or severe food insecurity in 2023 compared to the 1981–2010 average. Simultaneously, unsustainable food systems contributed to 11.8 million diet-related deaths in 2022, highlighting how agricultural choices directly impact human survival.
The economic burden is equally staggering. Delays in the adoption of clean, climate-friendly energy means over 2 billion people still use polluting and unreliable fuels in their homes. Across 65 countries with low access to clean energy, air pollution from the household use of dirty fuels resulted in 2.3 million avoidable deaths in 2022; including some of the 2.52 million deaths still attributable to ambient air pollution from the burning of fossil fuels globally.
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The cost of delay and subsidy shifts
Financial support for adaptation remains grossly insufficient. Dr. Marina Romanello, Executive Director of the Lancet Countdown at University College London, noted that scarce financial support is a key barrier. She explained that political shifts reducing foreign aid support from wealthy countries further restricts the financial resources needed to protect populations from these escalating risks.
While fossil fuel subsidies continue to drain public funds, the report highlights that local governments and the health sector are taking independent action. A growing number of cities are completing climate risk assessments, and the health sector has reduced its global greenhouse gas emissions by 16% between 2021 and 2022.