What is an El Niño?
An El Niño, first observed by Peruvian fishermen in the 1600s, is one of the earth’s most significant climate phenomena.
During an El Niño, the surface waters in the central and eastern Pacific Ocean become significantly warmer than usual.
But the impacts of El Niño reach far beyond the Pacific, influencing weather systems worldwide.
One of the impacts of climate change is increasingly variable, unpredictable weather, the effects of which may intensify during an El Niño period.
What is El Niño and La Niña?
- El Niño and La Niña are the warm and cool phases of a cyclical climate pattern — the El Niño-Southern Oscillation (ENSO).
- ENSO is the most important natural climate phenomenon driving year-to-year variations in the seasonal climate in many parts of the world.
- An El Niño state means warmer than usual sea-surface temperatures in the western Pacific – it has an irregular cycle of two to seven years and both El Niño and La Niña phases usually last nine to 12 months.
- The three-year-long La Niña period – which has been suppressing global temperatures – has come to an end and we are now in a neutral phase.
- There is a very high probability (90%) that an El Niño will emerge in the coming months.
Major El Niño events in the past 50 years have led to devastating floods, droughts, forest fires and coral bleaching. At least 26 El Niños were recorded in the 20th century.
El Niños vary in strength, with the 1997-98 El Niño the strongest ever recorded. Droughts struck Indonesia, Malaysia and the Philippines, while Peru faced heavy rain and floods.
The extreme weather associated with El Niño resulted in approximately 23,000 deaths worldwide.
What does this mean for global health?
The climate crisis is already a health crisis affecting millions. We know that global heating and extreme weather events, which are intensified in many regions by El Niño, have diverse impacts on our health, from infectious and respiratory disease escalation and malnutrition, to heat stress and mental illness.
While it is challenging to predict precisely how upcoming El Niño events will affect health globally, we know that its impact on the environment will have diverse health implications. Some of these will be positive, with more rain in drought-stricken areas and better climate predictability, but many will be negative.
Higher temperatures and health
In the event of an El Niño, significant heat transfer from Pacific waters into the atmosphere drives short-term increases in temperatures, particularly around the tropics.
El Niño events are part of natural climate variability. But when combined with human driven climate change, an upcoming El Nino could temporarily push global temperatures to new heights, beyond the critical threshold of 1.5 degrees Celsius.
The last very strong El Niño year, 2015-16, was the hottest since records began. Surpassing this limit could have severe consequences, such as extreme heatwaves, in turn driving various heat-related health impacts.
New data shows that 2022 was the fifth hottest year for Europe since records began. But scientists are warning that 2023 could be even warmer.
Rising temperatures directly contribute to heat-related deaths, with an estimated 30% of excess heat-related deaths attributed to climate change. This percentage is expected to rise as temperatures continue to climb.
Extreme heat can harm foetal development. For each degree Celsius increase in heat stress exposure, researchers found a 17% rise in foetal strain, measured by an elevated foetal heart rate and reduced blood flow through the umbilical cord.
El Niño and infectious diseases
El Niño conditions provide the perfect environment for many infectious diseases to expand their range.
Global heating means that more places are reaching suitable temperatures for disease transmission, and warming temperatures and shifts in precipitation during El Niño events create favourable conditions for pathogen survival and disease-carrying vectors like mosquitoes.
El Niño events escalate disease outbreaks and alter the spread of infections.
Past El Niños have driven a rise in malaria cases in Venezuela and Brazil, dengue outbreaks in the Pacific Islands, and cholera outbreaks in South India and Bangladesh.
Health risks of extreme weather events
El Niño can make extreme weather events more likely in certain regions, including extreme heat, droughts, storms and flooding.
Flood-related health risks are complex and multifaceted, ranging from hypothermia, drowning, undernutrition and injuries to infectious disease escalation and mental health problems.
Flooding in the 2016 El Niño displaced over 150,000 people in Paraguay, Uruguay and Argentina. As a result, Paraguay declared a health alert for mosquito-borne diseases like dengue.
In the same year, wildfires contributed to as many as 100,000 fatalities, while an estimated 60 million people across Africa, Asia, the Pacific and Latin America required food assistance.
With food systems already vulnerable to extreme weather, we are likely to see higher malnutrition rates due to crop failure and increased food insecurity.
El Niño’s cost to the global economy
El Niño events have severe, long-lasting impacts on country-level economic growth, particularly in the hardest-hit nations.
- Widespread droughts, wildfires, crop failures and disease escalation have direct, immediate-term costs and more enduring ones.
- Floods can disrupt supply chains, while droughts hinder agricultural production.
- A recent study calculated the average El Nino to cost the global economy approximately $3.4 trillion, with the 1997-98 El Nino costing an estimated $5.7 trillion.
El Niño and mental health
We know that climate change adversely impacts mental health in different ways.
During heatwaves, suicide rates, hospitalisations for psychiatric disorders, and emergency psychiatric visits have been shown to increase.
Global heating means people taking medications that disrupt the body’s ability to regulate temperature are particularly vulnerable in high temperatures.
Meanwhile, hospitalisations for climate-sensitive infectious diseases and coping with the long-term consequences of severe infections both compromise mental health.
An El Niño event could intensify all these impacts.
Who is most at risk from El Niño's health impacts?
The severity and nature of El Niño’s impacts on infectious disease spread, malnutrition, and respiratory and mental health varies across different regions.
The most affected areas include:
- Latin America (such as Peru, Venezuela and the Brazilian Amazon)
- Southeast Asia (the Philippines, Indonesia and Malaysia)
- West Africa
- the Horn of Africa
- Australia
- Pacific Islands.
These regions often struggle to cope with climate shocks, with those in low- and middle-income countries disproportionately affected. Coastal communities also bear a heavier burden due to an increased likelihood of storm-driven coastal flooding and erosion.
Preparing to protect health
Predicting the precise impacts of an El Niño event on health in different parts of the world remains challenging. However, significant progress has been made in accurately predicting El Niño events several months in advance.
This increased lead time is an invaluable opportunity for societies worldwide to enhance preparedness measures, ranging from emergency services readiness to strategic agricultural planning.
Putting health at the centre of El Niño preparedness and response
Alongside research efforts, we need political leadership at all levels to ensure the health impacts of El Niño are prominent on the global agenda. This is critical to drive action.
Wellcome is collaborating with governments, policymakers and stakeholders to raise awareness about the health risks associated with an El Niño event.
We want to see more collaborative partnerships at all levels: global, regional, and local, across El Niño-affected countries and between academia and research institutions, for example, to better understand the health risks and identify solutions.
Community and government collaboration
We must recognise the complex and multifaceted nature of the health impacts of an El Niño. Strategies should focus on building resilience, prioritising region-specific interventions, particularly among vulnerable populations.
By drawing on knowledge of the interplay between El Niño, climate change and health, we can develop preparedness measures and adaptation tools that address the unique challenges faced by different regions and mitigate the potential health impacts of El Niño.