Frequently Asked Questions

El Niño is a key part of the El Niño - Southern Oscillation (ENSO), the most important mode of ‘interannual variability in the Earth system’ – meaning that it’s the single most important factor that drives year-to-year ups and downs in the Earth’s weather.  Though the center of action of ENSO is in the tropical Pacific Ocean, it affects environmental conditions around the world through teleconnections (connections between really distant regions due to giant atmospheric and oceanic waves that move energy across the planet).  Year-to-year ups and downs in temperature, precipitation, and winds, as well as the incidence of severe weather (including hurricanes, tornadoes, and intense rainfall) are all linked to ENSO.

ENSO is caused by interactions between the atmosphere and ocean in the equatorial Pacific.  In this region, trade winds usually blow over the surface ocean from east to west, drawing up cool water from the deep ocean.  This creates a cold, nutrient-rich ‘tongue’ of water that covers a huge area of the equatorial Pacific Ocean, from the coast of South America, extending a couple thousand miles westward to the center of the Pacific Ocean.  

Sometimes, these trade winds speed up and this cold tongue grows much bigger – it can even extend nearly all the way across the equatorial Pacific (literally halfway across the planet), from South America to the Solomon Islands (close to Papua New Guinea).  This is a La Niña event – basically an intensification of the usual equatorial Pacific cold tongue.  

But when these trade winds slow down or even stop, cold water no longer rises up from the deep, and this whole area can suddenly become very warm.  This is an El Niño event.  This sudden switch from cold to warm causes major disruptions: fisheries off of Peru collapse for the year since there’s no more nutrient-rich water at the surface; rainfall shifts away from the equatorial West Pacific, which is usually a warm and wet area, to the Central Pacific, leading to droughts over SE Asia and Oceania; and huge waves ripple from the equatorial West Pacific Ocean to far reaches of the planet, disturbing temperature and precipitation patterns around the globe, including the Brazilian Amazon, Indian subcontinent, and African Sahel.

There are different ‘flavors’ of El Niño, just like there are different flavors of ice cream.  For example, there is the canonical El Niño, where the warm tongue of water extends from South America, but there’s also Modoki El Niño, where the warm tongue of water only extends over the central Pacific.  The prevalence of these two flavors (canonical versus Madoki) may have changed over the last several thousand years, though this is still the subject of scientific debate.

A Super El Niño is like an extreme version of El Niño.  It occurs when the Niño 3.4 index is greater than 2.0, meaning that temperatures over the equatorial Pacific are much, much warmer than the norm.  The impacts of a Super El Niño are much greater than a run-of-the-mill El Niño – much larger disturbances to temperature and precipitation patterns around the world, and even more extreme weather.  We’ve just emerged from a Super El Niño today; the last one before that was in 2015/16.  Whenever we get these Super El Niño events against a backdrop of a warming planet, we tend to see record-breaking heat, as El Niño usually leads to warmer-than-average global temperatures.

This index describes the ENSO state – are conditions like El Niño, La Niña, or neutral?  This index is calculated by measuring ocean temperatures in an enormous box covering the central equatorial Pacific Ocean.  

• When the Niño 3.4 Index is less than -0.5, it means that we’re in a La Niña state.

• When the Niño 3.4 Index is greater than 0.5, it means that we’re in an El Niño state.

• When the Niño 3.4 Index is between -0.5 and 0.5, it means that we’re in a neutral state. 

Flips generally occur between 1 to 3 years, which gives ENSO a periodicity of 2 to 6 years (e.g. the time it takes to go from one El Niño, to a La Niña, and to another El Niño). 

ENSO is responsible for a lot of the year-to-year volatility in the Earth system. So predicting it well gives governments and businesses the opportunity to mitigate risks, saving lives and billions in property losses.  Just a 1% improvement in the skill of ENSO predictions translates to (at least) $12B in global savings from reducing exposure. 

It depends on what industry you’re in, but if you’re in any industry that’s vulnerable to the elements, like agriculture, energy, insurance, logistics, and commodities markets, ENSO doubtlessly affects you. In fact, the last 2 major El Niño events have each been linked to $5T USD in economic losses globally, mostly within environmentally vulnerable industries.

On the other hand, knowing what ENSO state is on the way can provide the information needed to assess risk and ways to deal with this risk, like making plans to mitigate risk, transfer risk, and/or hedge risk through capital markets.