El Niño and the rise in disease outbreaks

People tend to associate el Niño with floods or drought. But did you know it also increases the risk of disease?

If you live in the coastal regions of the Pacific Ocean you will be much more familiar with this climate event. After all, fishermen have been aware of it since the 1600s. But in fact, we should all become acquainted with it as it is one of the most important naturally occurring climate cycles, that has worldwide repercussions.

What is El Niño?

So what is it? El Niño is a natural phenomenon that breaks the usual climate patterns around the Pacific Ocean. It is also a great example of how interconnected our world is, with events on one side of the world having major implications on the lives of people in a completely different part of the planet.

This El Niño, like many of its predecessors, could have an important effect on people’s health as it heightens the risk of hunger and infectious disease outbreaks.

Since childhood I have always found swimming in the Pacific Ocean in Ecuador cold. People who have never been to Ecuador are always surprised when I mention this - how can this be? It's the tropical pacific, no other region on earth receives as much sunlight!

But I started to understand what people meant the first time I had the pleasure of swimming in Indonesia and felt the water there to be much warmer than in Ecuador, even though both countries are on the equator!

It turns out there is a very reasonable explanation for this. And it's to do with wind and currents. For example, the Humboldt current that flows north from Antartica along the west coast of South America can make the ocean water around Ecuador as cool as 16 degrees Celsius. Did you know there are penguins in the Galapagos?!

But also, in normal conditions, easterly trade winds blowing from South America to Asia push the warm surface water in the Pacific Ocean westwards along the equator. To replace the displaced water, cooler, nutrient-rich waters rise up from the bottom of the ocean towards the surface of the South American equatorial coast.

As a result the water is at least 7C cooler in Ecuador than in Indonesia. As the cooler water is full of nutrients this makes it a very productive ecosystem supporting important fisheries.

What does it do?

El Niño is a natural cyclical event that disrupts this usual pattern. It seems to occur at irregular intervals of roughly 2-7 years, can last anything from 9 months to 2 years and can be very variable in its strength.

During an El Niño cycle, the trade winds tend not to blow as strong. Surface water is therefore not displaced westwards and no cooler water needs to rise up. As a result, during El Niño the waters in central and South America are much warmer, triggering a cascade of events.

For example, the higher temperatures shift the pacific jet stream southward from its normal position. The consequences of this change in winds, currents and water temperatures can be devastating.

With no rising of nutrient-rich water there is less phytoplankton and this impacts the entire food chain. Less phytoplankton means less food for fish, which in turn means less fish and consequently less seabirds and marine mammals that feed on the fish and so on.

Dry regions can become flooded with water in the Americas with increased mudslides and threatened livelihoods, while the monsoon in India and Indonesia can dry up with negative consequences on crop production, risk of coastal fires and important economic loss.

The consequences of El Niño are also felt in other areas. Northern Europe will tend to have colder and drier winters as a result of El Niño, while southern Europe has greater rainfall due to the shifting of the jet stream. The UK will conversely experience a drier and hotter summer. In the southern US, winters will be wetter than usual and the north will be warmer and drier.

The health impact

This El Niño, like many of its predecessors, could have an important effect on people's health as it heightens the risk of hunger and infectious disease outbreaks.

It threatens food security by putting additional pressure on farmers in certain parts of the world that are already suffering from the impact of rising temperatures due to climate change, the effects of COVID-19 and Russia's invasion of Ukraine.

The world should be preparing now for the rise in incidence of disease to reduce their intensity or even prevent the outbreaks, avoiding needless suffering and loss of lives.

These changes in weather patterns will affect the distribution of water-borne, food-borne or vector-borne diseases. For example, mosquitoes tend to stay away from cooler regions so people living at higher altitudes are usually safe from diseases like malaria, but during El Niño events we see disease transmission in high-altitude regions as a result of the warmer temperatures.

People in these regions are not regularly exposed to malaria so they have not had a chance to build immunity, and this puts them at increased risk of unfavourable outcomes.

This is not new stuff. Research has already shown connections between prior El Niño events and increases in diseases spread by mosquitoes such as Rift Valley Fever, chikungunya, Zika, but also cholera, plague and many others.

So what does this all mean for this El Niño 2023? It means we have the gift of foresight. With this declaration of an onset of El Niño, we have an early warning sign.

The world should be preparing now for the rise in incidence of disease to reduce their intensity or even prevent the outbreaks, avoiding needless suffering and loss of lives.

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This article was originally published on Marta's LinkedIn on 16 August 2023.