Lancet: Health Impacts of Climate Change Are Accelerating

A decade after the Paris Agreement set the ambition of limiting global warming to 1.5°C above pre-industrial levels, the Lancet warns that the health impacts of climate change are accelerating faster than the global response.

Against this backdrop, the Lancet Countdown Report calls for climate change to be recognised as a public health emergency, requiring a globally coordinated, long-term response.

Produced by an international collaboration of 146 researchers and more than 100 institutions, led by University College London (UCL) and developed in strategic collaboration with the World Health Organisation (WHO), the report tracks global trends across 54 indicators related to climate change and health.

The Lancet Countdown’s annual assessment examines the health impacts of climate change alongside the potential benefits of interventions designed to address it.

Chief among the report’s concerns is the growing toll of extreme heat. Between 2016 and 2023, heat was associated with an average of 540,800 deaths annually, with climate change responsible for 68% of these deaths, up from 55% between 2006 and 2015. 

In 2023 alone, heat-related deaths reached a record 710,000, exceeding the annual death toll attributed to malaria or HIV, according to the report.

Alongside its findings, the Lancet Countdown and WHO have signed a Memorandum of Understanding (MoU), strengthening collaboration on global monitoring and action addressing health and climate change.

Reflecting on the report, WHO Director-General Dr Tedros Adhanom Ghebreyesus says: “The evidence is undeniable: climate change is one of the greatest threats facing humanity. Its impacts are already being seen through worsening heat stress, extreme weather events, food insecurity and disease.”

However, he also sees opportunities for progress. “This report also reminds us that solutions are within reach,” he continues. “By placing health at the heart of climate policies we can save millions of lives, build more resilient societies and deliver a healthier future for all.”

The headwinds facing health’s response to climate change

Despite the past 11 years being the hottest on record, the report warns that global public health systems are struggling to respond to escalating threats.

More frequent heatwaves and severe droughts are damaging human health and threatening food security. Meanwhile, changing rainfall patterns are increasing the number of people exposed to environmental conditions conducive to the transmission of diseases such as dengue and malaria, as well as infections caused by Vibrio bacteria.

The consequences extend beyond direct illness and mortality, threatening economic development and, in turn, the resources available to protect public health. In 2025, heat exposure resulted in the loss of 573 billion potential working hours, equivalent to US$1.07tn in lost income.

“A decade after the Paris Agreement, our findings are unambiguous: the health harms of climate change are growing faster than the world’s response to them, and in many cases even accelerating,” says Professor Marina Romanello, Executive Director of the Lancet Countdown at UCL.

Adaptation efforts are also failing to keep pace with the scale of the challenge. By 2025, 75.8% of WHO Member States had not reported completing a climate vulnerability and adaptation assessment since 2020. 

These assessments are an essential first step towards developing evidence-based responses. Meanwhile, 71.1% had not reported developing a Health National Adaptation Plan to guide action and support resource mobilisation.

Political and corporate engagement is also declining. The proportion of countries mentioning the relationship between climate change and health in their UN General Debate speeches fell from 65.9% in 2021 to 26.3% in 2025. 

Among companies, the share discussing the issue in their UN Global Compact reports dropped from 58% in 2023 to 37% in 2025.

The energy situation

While the report acknowledges progress in global energy markets, it argues that the transition remains too slow, with energy systems still heavily dependent on fossil fuels.

Investment in clean energy reached a record US$2.1tn in 2025, 82% higher than investment in fossil fuels. However, fossil fuels still accounted for 80.7% of global energy supply. 

Although the share of electricity generated from modern renewables increased from 5.5% in 2016 to 13.5% in 2023, rising energy demand pushed energy-related greenhouse gas emissions to a record high in 2024.

The report also highlights the continued scale of investment in, and subsidies for, fossil fuels, arguing that these remain significant barriers to progress.

Nevertheless, the shift towards cleaner energy is already delivering public health benefits. Improvements in indoor air quality associated with the energy transition prevented an estimated 400,000 deaths in 2023 compared with 2016.

A tool for change

Against the backdrop of rapidly shifting global climatic conditions, the report calls for the WHO to develop a mechanism capable of formally recognising climate change as a global health emergency.

Currently, the WHO’s highest level of international health alert is a Public Health Emergency of International Concern (PHEIC), a designation intended primarily for events requiring a coordinated international response, such as Ebola outbreaks.

The report’s authors argue that climate change requires a different, longer-term approach, reflecting its sustained and interconnected impacts on health.

Such a mechanism could help coordinate government agencies, improve resource allocation and facilitate the rapid sharing of data, supporting a more unified response to the growing public health threat.

By placing health at the centre of climate policy, the report argues, governments have an opportunity not only to reduce the risks associated with a warming planet but also to improve health outcomes and build more resilient healthcare systems.

The Lancet Countdown - key partners

World Health Organisation (WHO)

Director-General: Dr Tedros Adhanom Ghebreyesus | HQ: Geneva, Switzerland

The World Health Organisation is the United Nations agency responsible for international public health. It coordinates global health initiatives, develops evidence-based guidance, establishes health standards and supports countries in strengthening healthcare systems. Its collaboration with the Lancet Countdown supports international monitoring and action on climate change and health, helping governments understand emerging risks and develop evidence-informed responses.

Gavi, The Vaccine Alliance

CEO: Dr Sania Nishtar | HQ: Geneva, Switzerland

Gavi, the Vaccine Alliance is a global public-private partnership working to expand equitable access to immunisation in lower-income countries. Bringing together governments, international organisations, manufacturers and philanthropic partners, Gavi helps finance vaccine programmes and strengthen health systems. Its work is relevant to climate-related health risks, as changing environmental conditions can influence infectious disease patterns and increase pressure on vulnerable populations and healthcare services.

University College London (UCL)

President: Dr Michael Spence | HQ: London, UK

University College London is a leading multidisciplinary research university and a major centre for medical, scientific and public health research. UCL leads the Lancet Countdown collaboration, bringing together international researchers to monitor the health consequences of climate change and assess the benefits of climate action. Its work connects scientific evidence with policy, helping inform decisions on healthcare resilience, climate adaptation and population health.