A new study by Climate Central reveals that human-caused climate change has dramatically intensified global exposure to extreme heat, affecting billions with more frequent and severe dangerous temperatures over the past year.

A comprehensive analysis released by Climate Central, in collaboration with World Weather Attribution and the Red Cross Red Crescent Climate Centre, has quantified the profound impact of human-induced global warming on extreme heat worldwide. Covering the 12-month period from May 1, 2024, to May 1, 2025 – which included Earth’s hottest year and hottest January on record – the report shows that climate change is no longer a future threat but a current driver reshaping daily life for nearly half the planet’s population.

The key metric defines “extreme heat” as temperatures hotter than 90 per cent of historical observations in a given location during the 1991-2020 baseline period. The findings are stark: approximately 4 billion people, representing about 49 per cent of the global population, endured at least 30 days of such extreme heat made more intense or likely by climate change. This exposure translates to heightened risks of heat-related illnesses, reduced labour productivity, strained energy systems, and threats to vulnerable groups including the elderly, children, outdoor workers, and those without access to cooling.

Widespread Doubling of Heat Days Across Nations

The study examined data across nearly 200 countries and territories. In 195 of them, human-caused climate change – at least doubled the number of extreme heat days compared to a counterfactual world without fossil fuel emissions and other anthropogenic influences. Primary drivers include emissions from burning coal, oil, and methane gas, which trap heat in the atmosphere and amplify temperature extremes.

All 67 significant extreme heat events during the period – selected based on record-breaking temperatures or major societal and economic impacts – were found to bear the fingerprint of climate change. These events ranged from deadly heat waves in densely populated regions to prolonged high temperatures disrupting agriculture and infrastructure. The analysis underscores that climate change not only makes individual hot days more probable but extends the duration and frequency of heat waves, turning what were once rare occurrences into seasonal norms.

Health and Societal Risks Amplified

Extreme heat is already the deadliest form of weather-related hazard in many parts of the world, claiming thousands of lives annually through heatstroke, cardiovascular strain, and exacerbated chronic conditions. The report highlights how added heat days increase health vulnerabilities, particularly in tropical and subtropical zones where baseline temperatures are high and cooling access limited.

Beyond direct health effects, intensified heat disrupts economies by reducing worker output in agriculture and construction, straining power grids during peak demand, and threatening food security through crop stress. The findings align with broader trends observed in Climate Central’s ongoing work, such as rising risky heat in urban areas, extended summer seasons, and generational disparities where younger people face far more extreme heat days than previous cohorts.

Urgent Call for Action Amid Escalating Trends

Released ahead of Heat Action Day, the report emphasises the need for immediate adaptation and mitigation measures. These include expanding early warning systems, investing in heat-resilient infrastructure, promoting urban greening to combat island effects, and accelerating the global shift away from fossil fuels to curb further warming.

While natural variability plays a role in weather, the consistent attribution to human influence across events and regions leaves little doubt: emissions reductions are essential to prevent even worse escalation. As global temperatures continue to rise, unchecked, the number of people exposed to dangerous heat could grow substantially, affecting quality of life, equity, and development worldwide.

The study leverages tools like the Climate Shift Index to attribute temperature changes, providing a scientific basis for policy and public awareness. Experts urge governments, communities, and individuals to prioritize heat action plans and support international climate commitments to limit warming and protect populations from this escalating crisis.