As the UN’s climate summit, Cop29, gets underway in Azerbaijan this week, the effect of climate change on human health is high on the agenda. And rightly so, amid some alarming emerging statistics. By the end of this century, climate change could be the cause of more than 3 million deaths per year (around five times as many annual deaths globally of HIV and Aids).

A new report from a scientific review committee of experts called the Lancet Countdown highlights how globally people are facing “record-breaking threats” to their health as a consequence of climate change. The major climate risks include negative effects on food security (including production), spread of diseases, ecosystems, infrastructure and the economy.

Despite having contributed the least to global emissions, Africa will be most affected by climate change. This is due to the fragile economics and exposure to extreme weather events across much of the continent. But all continents, including Europe, will be negatively affected.

Everyone working in health needs to prepare for and be equipped to respond to the health consequences of the climate crisis. The Lancet highlights the opportunity “to redefine the social and environmental determinants of health”.

These are the top five priorities when it comes to climate change and human health:

1. New and emerging infectious diseases

Drastic environmental change increases the risk of catching deadly infectious diseases such as malaria, dengue and West Nile virus in new areas. Modelling shows that mosquito populations could move into different regions of Africa and South America, and into Europe. The parasitic ticks that transmit the Crimean-Congo haemorrhagic fever virus may move north from Africa into Europe as climate change takes hold.

The threat of outbreaks of new and emerging infections, and pandemics, is increasing. In 2022, the World Health Organization warned that Ebola outbreaks around Africa are becoming more frequent due to climate change, as bats – the likely source of the virus – migrate and seek new habitats to breed.

Infectious diseases are predicted to spread more easily due to climate change, and thus increase the risk of pandemics. This threat includes Lassa fever, a virus thought to be transmitted by rats. Modelling has indicated that the rats may flee fire and flood, find new habitats and thus expose greater numbers of humans to new or different viruses.

2. Food security and nutrition

Climate change exacerbates food insecurity. In Ghana, West Africa, inconsistent rainfall during the 2024 rainy season has left an estimated 1.05 million people acutely food insecure. This is the case particularly in the north of the country, an area already with a high level of food insecurity and hunger.

The UN predicts that more than 600 million people will be living in hunger by 2030, due to the impact of climate shocks and lack of aid and government action thus far.

Climate change worsens food insecurity from many different angles; from rural farmers in Ghana losing their crops due to unexpected changes in rainfall, to the impact of affordability of imports in the UK, there won’t be just hunger hotspots.

As food insecurity deteriorates, so will malnutrition globally. By 2030, between 570,000 and 1 million children under five years old will suffer from stunted growth due to climate change, also exacerbating their vulnerability to infectious diseases such as malaria.

3. Access to healthcare

Extreme weather can physically prevent people from accessing healthcare. Between 2014 and 2023, 61% of land globally experienced an increase in the number of days of extreme rainfall, compared to 1961-1990.

Flash floods have devastated Valencia in Spain, with health services anticipating increases in diarrhoea, skin infections and hepatitis A. Evidence from Ghana shows that physical access to healthcare is restricted, with patients and sometimes health workers unable to reach local health centres, and emergency referrals unable to reach hospitals.

The Lancet report also found that only two-thirds of countries had high or very high implementation of legally required health emergency plans. This number needs to be 100% to protect population health as extreme weather events become more frequent, unpredictable and severe.

Delays to reduce carbon emissions and attempt to rectify the situation are only adding to the issue. Global energy-related carbon emissions reached a new high in 2023, showing little signs of slowing down.

In a 2023 study conducted in Mion (northern Ghana), nearly all participants reported not being able to access a healthcare facility when they needed to at least once, due to climatic conditions. Similarly, in the Volta region in Ghana, many residents lost all their belongings during unexpected flooding in 2023 including health insurance documents. This means people cannot access vital medications or services such as insulin if diabetic, or emergency care.

4. Air quality

Air quality is one of the most locally-felt impacts of climate change, especially in heavily industrialised countries. The UK Health Security Agency estimates that around 36,000 deaths annually are attributable to air pollution in the UK, with this number jumping to 2 million in China.

This is in part due to causing new, or exacerbating existing, chronic respiratory conditions such as asthma and chronic obstructive pulmonary disease, which one in five people suffer with in the UK. It also reduces life expectancy through prolonged exposure, causing diseases such as coronary heart disease and lung cancer.

5. Extreme heat

In 2023, increased heat exposure put those engaged in outdoor physical activity (which includes everything from agricultural labour to recreational running) at risk of heat stress for 28% more hours than two decades ago.

Heat stress has been associated with debilitating issues such as kidney stones, exhaustion, asthma and heart attacks. Any amount of activity or movement in rising temperatures will put individuals at great risk of these conditions. This will compromise income if labour is based outdoors, population health if we can do less outside, and the ability to enjoy the outdoor world.

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Michael Head, Senior Research Fellow in Global Health, University of Southampton and Jessica Boxall, Public Health & Nutrition Research Fellow, University of Southampton

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