What Makes El Nino So Dangerous?

If you’ve been paying attention to weather forecasts lately, you may have heard that not only are we experiencing El Nino this year, but that it’s also one of the strongest on record. Because the climate pattern develops every few years, you’ve likely heard the name before and know it has something to do with the weather.

But what exactly is El Nino, and why should we take a “super El Nino” so seriously? 

Depending on where you live, the latter question may be especially important, because El Nino can create very dangerous conditions across much of the globe, including flooding and drought.

Not only that, but the weather event can last for several months, if not longer. That makes this a good time to understand how El Nino forms and why it reshapes weather around the world.

El Nino Gives Warm Weather a Push

El Nino is the warm phase of a natural climate cycle called the El Nino-Southern Oscillation, or ENSO. The cycle has three phases: El Nino, La Nina, and a neutral period in between. Together, they reflect an ongoing conversation between the central/eastern tropical Pacific Ocean and the atmosphere above it.

To understand El Nino, it helps to start with what happens during a typical year. Strong trade winds blow steadily from east to west across the equatorial Pacific, pushing warm surface water toward Asia and Australia. 

As that warm water piles up in the western Pacific, cold, nutrient-rich water rises to the surface off the coast of South America in a process called upwelling. This cold water supports some of the world’s richest fisheries, and it’s a good thing for the whole marine food web.

During an El Nino, however, those trade winds weaken — sometimes they even reverse. Without the winds pushing it, warm surface water begins to spread back eastward across the Pacific toward the Americas. The usual upwelling of cold water is suppressed, allowing sea surface temperatures in the central and eastern Pacific to climb well above average.

It’s Everyone’s Problem

That shift may seem local, but it changes where heat and moisture are released into the atmosphere. Because warm ocean water heats the air above it, the main zone of rising air and thunderstorms moves as well. One of the biggest consequences is a shift in the jet stream, the fast-moving river of air high in the sky that helps steer storms across North America. 

During many El Nino winters, the Pacific jet stream strengthens and shifts farther south. This often brings wetter-than-average conditions to the southern United States, including California and the Gulf Coast, while parts of the northern U.S. and Canada tend to experience milder and drier winters. 

The powerful 1997-98 El Nino, for example, helped create what some journalists called “the year without a winter.” The shift can also fuel more thunderstorms and lightning in parts of North America, and some studies have found that El Nino years are associated with increased tornado activity as well.

But El Nino’s influence extends far beyond North America. Peru and parts of South America often experience heavy rains and flooding. Eastern Africa may become wetter than normal. Meanwhile, Australia, Indonesia, and parts of Southeast Asia are more likely to face drought, increasing the risk of wildfires and crop failures.

How El Nino Got Its Name

Ocean ecosystems also feel the effects: The 2015–16 El Nino contributed to a global coral bleaching crisis that devastated large sections of Australia’s Great Barrier Reef, for example. And the loss of nutrient-rich cold water off the coast of Peru reduces its fish population, something noticed by fishermen even centuries ago.

In fact, these fishermen along the Pacific coast of Peru noticed that warmer water and the resulting threat to their livelihood seemed to occur every few years, peaking in late December. Because the warming coincided with the celebration of Jesus’ birth, they called the phenomenon El Nino de Navidad, which translates to “the Christmas Child.”

So What Is La Nina?

La Nina (Spanish for “the little girl”), meanwhile, represents the opposite phase of the cycle. In a La Nina year, trade winds become stronger than usual. Cold water thus wells up more vigorously in the eastern Pacific, and many of El Nino’s typical weather patterns are reversed. The Pacific Northwest often becomes cooler and wetter, the southern U.S. tends to be drier, and Atlantic hurricane seasons are generally more active.

Scientists still don’t fully understand what causes the ENSO cycle to flip between its different phases, though it emerges from complex feedback cycles between ocean temperatures, winds, and atmospheric pressure across the tropical Pacific. El Nino events typically develop every two to seven years, usually beginning in spring or early summer, peaking during the winter months, and lasting roughly nine to 18 months.

Although El Nino strongly influences weather, it doesn’t dictate it. Other climate patterns, day-to-day weather variability, and long-term climate change all continue to shape what ultimately happens in any particular place. Meteorologists often say El Nino “tilts the odds” rather than guaranteeing specific outcomes. 

But, with the 2026-27 El Nino coming in hot (literally) as one of the strongest to date, the odds are tilted more than usual.