Across the world, people have felt the impacts of climate change firsthand. The northern hemisphere has had another record-breaking summer season of heat and extreme weather events. The south now faces a summer of heatwaves, flooding, wildfires and droughts. This is driven by decades of climate change, now supercharged by an unprecedented El Niño – the warm phase of the El Niño Southern Oscillation, which is a cyclical warming and cooling of the Pacific ocean driven by changing trade winds, with global impacts on the climate.
Extreme events driven by climate change have displaced entire communities in recent cyclones and floods in Nepal. More than 250,000 people lost everything in a recent wildfire in Spain. In European cities, over 50,000 are reported to have died from heat in the past summer, over 65% of those deaths being directly attributable to climate change. These events underscore the reality that climate change is not some future risk scenario. It’s an immediate threat to the world’s most vulnerable communities and people.
As public health researchers and professionals seeking to understand and respond to the health impacts of climate change, this is of great concern to us. In our own work, on the impact of heat on pregnant women and children in Africa, we have found far-reaching impacts on the health of the mother during pregnancy, on poor birth outcomes, and potentially lifelong problems for unborn children. In an earlier study, we also found that the healthcare workers tasked with caring for these vulnerable communities were negatively affected by climate change.
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Heat exposure during pregnancy can lead to a lifetime of health problems
Most recently, we worked, through research with communities in South Africa, to understand the ways people try to adapt to climate change. It is increasingly clear that communities know about the risks they face from climate change. They experience these daily. They simply do not have the resources to adapt to these changes.
The World Health Organization (WHO) and leading scientists have for decades considered climate change to be the greatest health threat in the 21st century. However, instead of having a global health architecture that is ready to pre-empt and respond to climate change, we, as public health professionals, have left the responsibility to a UN system built on consensus. Progress has been painfully slow, and more recently, completely stalled. Despite successive commitments, the world has failed its goal of preventing warming of 1.5°C.
It is with this in mind that we call for the WHO to declare the health impacts of climate change a Public Health Emergency of International Concern (PHEIC). This declaration would galvanise political will, mobilise financing and provide evidence-based recommendations for an urgent public health response.
Health impacts of climate change
The health impacts of climate change are widespread, compounding the vulnerability of individuals and health systems. The elderly, pregnant women and children, and those living with chronic illnesses are the most at risk of suffering impacts. But these populations often have the least resources to adapt. Similarly, those in the global south are the most affected by climate change and generally contribute to it the least.
For these groups, climate change means another season of crop failures that leaves their children malnourished; a flood that cuts them off from their local clinic and the medication that keeps them healthy, and alive; a malaria season that means losing a child or a friend to a preventable disease; a pregnancy that ends in heartbreak during a heatwave.
New scientific approaches, like impact attribution, are being developed to show exactly how much climate change is contributing to these adverse health outcomes. This strengthens the public’s confidence in the scientific consensus.
A narrow window to respond as El Niño intensifies
The world now faces an unprecedented El Niño season. A recent report forecasts 451,000 additional heat-related deaths from June 2026 to February 2027. This is roughly equivalent to the number of deaths due to COVID-19 in the first six months of the pandemic.
The WHO has a mechanism to deal with unprecedented threats to public health, especially those that require international collaboration. The International Health Regulations set out very clearly the processes and actions that must be taken in response to a potential Public Health Emergency of International Concern. This is defined as:
an extraordinary event that (i) constitutes a public health risk to other States through the international spread of disease, and (ii) potentially requires a coordinated international response.
To trigger a potential Public Health Emergency of International Concern, the International Health Regulations prescribe that two of the following four conditions be met:
- Is the public health threat serious?
- Is the event unusual or unexpected?
- Is there significant risk of international spread?
- Is there a risk of international travel or trade restrictions?
Call to action
Many have called for such a declaration in response to the climate crisis, which meets most of, if not all, the criteria. We have argued elsewhere that any further delays will result in needless loss of life, and preventable harms to the most vulnerable in society. This urgent call has been supported by health ministries across Africa, including Senegal, Namibia and Zimbabwe.
Declaring a Public Health Emergency of International Concern would enable an equitable response rooted in the principles and ethics of public health: care and support for those most affected; large-scale prevention; and surveillance of impacts. It would enable international collaboration, catalyse finance and ensure central coordination and support from the WHO.
It is time for countries to trigger the International Health Regulations process and have an expert committee assess the risks we face and provide recommendations to respond. It is time for WHO to declare a Public Health Emergency of International Concern, and for us to face this threat together as an international community, before it is too late.
Nicholas Brink receives funding from the HE2AT Center (U54TW012083) and HarmonAIze (3U54TW012083–04S1) grants supported through the Fogarty International Center by the National Institutes of Health and National Institute of Environmental Health Sciences; BioHEAT (227204/Z/23/Z), Global Heat Attribution Project (309105/Z/24/Z), Heat Adaptation for Pregnant Women and Infants study (226758/Z/22/Z), and Southern African Consortium for Climate Change and Health (336423/Z/25/Z) grants supported by the Wellcome Trust; HIGH Horizons, funded from the EU’s Horizon Framework Programme (101057843) and UK Research and Innovation (10038478); and the Climate Change in Ireland Study (2025-HE-1304).
F. Machingura declares institutional research funding from the Wellcome Trust, administered through CeSHHAR Zimbabwe, to support her contribution to this correspondence through the Southern African Consortium for Climate and Health, Science and Policy Centres (336423/Z/25/Z); declares institutional research grants from the European Union (grant number 101057843), UK Research and Innovation (grant number 10038478), Wellcome Trust (309105/Z/24/Z and 226758/Z/22/Z), and Sanofi; is the Technical Secretariat Lead for the Zimbabwe Intersectoral Coordination Cluster on Climate, Environment and Health; is the Zimbabwe Country Director and Regional Lead for Climate–Health Policy, Implementation Science and Financing for the Wellcome Southern Africa Climate and Health, Science and Policy Consortium; is the Director of Climate, Environment and Health for CeSHHAR Zimbabwe; is a Lecturer at the Liverpool School of Tropical Medicine; and is a member of the Heat–Maternal, Newborn and Child Health Indicator Group for WHO and the World Meteorological Organization.
Matthew Chersich and Robb Butler: do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
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