New findings presented in the 2025 Lancet Countdown on Health and Climate Change reveal a dire global crisis: the persistent reliance on fossil fuels and inadequate adaptation measures are translating into devastating health consequences worldwide. The annual report, now in its ninth year and published by The Lancet—one of the world’s preeminent medical journals—details that over half of the 20 key health-related climate indicators have reached unprecedented levels, signaling a worsening and accelerating public health emergency linked to climate change.
The report synthesizes data from 128 experts across 71 academic institutions and United Nations agencies, offering a comprehensive, evidence-based overview of how climate change impacts health. The Countdown divides its analysis into five working groups focusing on different facets of climate and health. Notably, the University of Sydney’s Heat and Health Research Centre plays a pivotal role as the host institution of Working Group 1, the team responsible for the largest cohort of health impact indicators, including heatwave exposure and the effects of heat on physical activity.
Among the most alarming revelations, air pollution originating from the combustion of fossil fuels directly contributes to approximately 2.5 million deaths annually, marking it as a leading preventable cause of mortality worldwide. This staggering figure underscores the human toll exacted by continued fossil fuel dependency, despite mounting evidence supporting cleaner alternatives. Meanwhile, heat-related mortality has surged dramatically, increasing by 23% since the 1990s. Between 2012 and 2021, heat-related deaths averaged 546,000 per year, further exacerbated by record-breaking temperatures in 2024.
The year 2024 stands out as humanity’s hottest on record, with the average global citizen experiencing an unprecedented 16 additional days of extreme heat attributable to climate change. Vulnerable populations, including infants and seniors above 65, faced an even more dire reality, enduring an average of 20 heatwave days, corresponding to increases of nearly 400% and 300%, respectively, from historical baselines. Such prolonged exposure to heatwaves carries profound physiological implications, straining thermoregulatory capacity and exacerbating cardiovascular and respiratory illnesses.
Concurrently, hotter and drier global conditions fueled an increase in wildfires, which released fine particulate matter (PM 2.5) that is especially harmful when inhaled. The report estimates 154,000 deaths globally were linked to wildfire smoke in 2024, representing a 36% rise compared to yearly averages in the early 2000s. These particulates penetrate deep into lung tissue and can trigger systemic inflammation and aggravated chronic diseases, compounding the public health burden amid ongoing climatic stressors.
Economic impacts mirror this health crisis. Heat exposure led to an estimated 639 billion potential hours of lost labor productivity in 2024 alone, translating into income deficits around US$1.09 trillion—nearly 1% of the global gross domestic product. Moreover, the demographic segment over 65, particularly susceptible to heat-related fatalities, incurred estimated economic costs nearing US$261 billion, emphasizing the pressing need for adaptation strategies that protect the most vulnerable.
Food security also remains precariously linked to climatic fluctuations. Droughts and heatwaves contributed to an increase of 123 million people facing moderate or severe food insecurity in 2023, relative to typical levels between 1981 and 2010. This connection highlights the intricate nexus between climate anomalies, agricultural productivity, and nutritional outcomes, which collectively threaten global health through malnutrition and associated morbidities.
Pollution burdens from household energy use spotlight inequities within this crisis. In 65 countries with limited access to clean energy technologies, 2.3 million avoidable deaths in 2022 were attributed to indoor air pollution from dirty fuel combustion. This issue overlays with the 2.52 million deaths from outdoor air pollution caused by fossil fuels globally, revealing a dual front where energy poverty and fossil fuel reliance jointly imperil human health, particularly in low-resource settings.
Dietary patterns, often overlooked in climate-health discourse, were responsible for 11.8 million diet-related deaths in 2022. These outcomes are closely linked to high-carbon, unhealthy diets, underscoring the potential for mitigating climate change and improving mortality through transitions to sustainable, healthful food systems that prioritize plant-based nutrition and reduced greenhouse gas footprints.
Environmental degradation compounds these challenges. The report documents the destruction of over 128 million hectares of forest in 2023, a 24% increase from the previous year. This deforestation undermines nature’s capacity to sequester carbon dioxide, aggravating climate change trajectories and, consequently, their associated health impacts, such as vector-borne diseases and respiratory conditions.
Alarmingly, some of the world’s largest CO2 emitters have subsidized fossil fuel industries at levels exceeding their national health budget allocations. Fifteen of eighty-seven high-emission countries spent more government resources on fossil fuel subsidies than on health in 2023, reflecting systemic policy misalignments that hinder climate and health progress. Globally, fossil fuel subsidies reached an extraordinary $956 billion, while oil and gas corporations are planning production expansions triple the amounts sustainable for a livable climate by 2040.
Financial institutions play a consequential role in this dynamic. The top 40 private lenders to fossil fuel sectors funneled a record $611 billion toward fossil fuel expansion in 2024, a 29% increase from the previous year. This financing outpaces green energy investments by 15%, indicating persistent challenges in aligning capital flows with climate-compatible pathways and health-positive development.
Yet, amid these sobering trends, the report identifies hopeful signs of resilience and transformation. Local governments have increasingly prioritized climate risk assessments, with 834 of 858 cities reporting completed or planned assessments in 2024, enabling better preparedness and targeted interventions. The health sector itself demonstrated leadership, reducing its greenhouse gas emissions globally by 16% between 2021 and 2022, showcasing the feasibility of sustainable operations in a traditionally resource-intensive sector.
Education emerges as a foundational pillar for progress. Nearly two-thirds of medical students worldwide incorporated climate and health education into their curricula in 2024, equipping the next generation of healthcare professionals with essential competencies to address climate-related health challenges. Moreover, shifts away from coal usage, particularly in affluent countries, prevented an estimated 160,000 premature deaths annually between 2010 and 2022 through reductions in particulate air pollution exposure.
Renewable energy adoption continues to scale up, with modern renewables supplying a record 12% of global electricity generation in 2022. This clean energy transition not only curtails emissions but also fosters sustainable job creation, aligning economic and environmental objectives with health benefits. These actions accentuate the multiplicity of co-benefits achievable through climate mitigation and adaptation policies that centre human health.
Professor Anthony Costello, Co-Chair of the Lancet Countdown, emphasizes the urgent need for multisectoral efforts to prevent regression in climate and health gains. He highlights the vital role of “all hands on deck” to secure a just and equitable transition that prioritizes health protection worldwide. Without accelerated policy shifts that centre human health, the report warns, the cumulative impacts of climate change will exact mounting, irreversible human costs.
At the University of Sydney, the Heat and Health Research Centre, led by Professor Ollie Jay, continues to spearhead global scientific contributions informing this vital report. The Centre addresses crucial issues relating to heat vulnerability and physical activity under heat stress, producing data-driven evidence essential for shaping adaptation strategies. This dedicated research cadre reflects the critical importance of integrating rigorous, targeted science into policy frameworks to mitigate the climate-health nexus.
The 2025 Lancet Countdown report stands as a clarion call for immediate and comprehensive action. It exposes the systemic failures that allow continued fossil fuel dependence at immense human cost while also illuminating the pathways for health-centered, equitable climate solutions. As climatic threats grow more acute, the synthesis of scientific insight and political resolve remains indispensable to safeguarding global health and ensuring a sustainable future for coming generations.
Subject of Research: People
Article Title: The 2025 report of the Lancet Countdown on health and climate change
News Publication Date: 28-Oct-2025
Web References:
References: The 2025 Lancet Countdown on Health and Climate Change Annual Report, Wellcome Trust Grant #304972/Z/23/Z, Research Council of Finland VFSP-WASE #359421, EU Horizon Projects FirEUrisk #101003890 and ClimAir #101156799.
Keywords: climate change, health impacts, fossil fuels, air pollution, heatwaves, mortality, food insecurity, wildfire smoke, labor productivity, renewable energy, climate adaptation, health sector emissions.
