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How Ocean Climate Change Impacts El Niño and La Niña

Emily Heaslip

El Niño and La Niña are climate patterns that occur irregularly every two to seven years in the Pacific Ocean. The scientific name for this phenomenon is the El Niño-Southern Oscillation (ENSO) cycle. 

El Niño occurs more frequently than La Niña. This event takes place when warm water builds along the Equator in the eastern Pacific ocean. Warm water upwells to the surface, warming the atmosphere and causing moisture-rich air to rise. Storms start to form, bringing intense rain to certain parts of the world. Winds also shift: low-level surface winds that normally blow from east to west weaken, or even start blowing from west to east. 

With La Niña, the opposite effect takes place. Cold water at the surface of the ocean brings down the air temperature of the atmosphere. Less water evaporates, and as a result, there’s a drier season in places like Peru, Ecuador, and the southeastern United States. Normal easterly winds intensify.

El Niño and La Niña impact global weather, climates, ecosystems, and even our economy. As climate change intensifies, scientists are anxious to see how ENSO will change accordingly — yet limited data on this phenomenon makes it difficult to predict the future. 

What causes El Niño and La Niña? 

It’s actually not clear what causes the El Niño cycle to begin. Scientists have learned to identify signs that El Niño is “brewing”, but there’s no consensus as to what triggers this phenomenon to happen. 

What happens when an El Niño and La Niña take place? When trade winds die, it causes two effects. First, the wind-forced upwelling that brings cool water from the depths to the surface slows. Warm water that has pooled in the western part of the Pacific “sloshes” back toward the east. As warmth spreads east across the Pacific, that causes trade winds to become even weaker. 

“So there’s a double whammy: the chilly waters that usually help cool down the South American coast stay trapped deep below the surface, and the winds that would help cool things down stagnate,” explained National Geographic.

Scientists are still trying to fully understand this phenomenon, but what is known is that ENSO has a serious impact on the health of our planet. In the Pacific, upwelling brings nutrient-rich water from below the surface, feeding phytoplankton: a critical organism in the food chain. When upwelling slows, phytoplankton don’t receive enough nutrients, population decreases, and the entire food chain is affected. 

The opposite phenomenon is true with La Niña. Off the Pacific Coast of the US, colder waters bring up more nutrients than usual, attracting squid and salmon to places like California. 

When ENSO takes place, its effects aren’t limited to the Pacific Ocean. “During El Niño years, for example, fewer hurricanes whirl across the Atlantic than usual, and the ones that do are likely to be fairly weak,” wrote Nat Geo. “And rainfall patterns shift across the globe: California and the Horn of Africa dampen, for example, while the rains that generally drench India during monsoon season weaken, and the Indian subcontinent dries out slightly.” 

Understanding El Niño and La Niña has proved difficult, and climate change is only complicating efforts to prepare for and manage the effects of ENSO. 

Ocean climate change: El Niño and La Niña effects

There’s plenty of scientific evidence to show that climate change causes extreme weather to get more extreme. And, some models indicate the same is true for ENSO. We could start to see warmer, wetter El Niños and drier La Niñas as climate change continues. 

Other models predict more frequent extreme El Niño and La Niña events. Frequently strong ENSO events could be a serious problem for regions that already struggle with strong El Niño effects. 

“Losses from the El Niño in 1997-1998 included thousands of deaths and injuries from severe storms, heat waves, fires, floods, frosts, and drought. Estimates of El Niño-related damage ranged from $32 to $96 billion,” reported the UN.

In 2016, the last time we had a strong El Niño, coral bleaching in the Pacific increased, fires fueled by drought-ravaged Australia, and South America faced massive floods. Scientists fear that climate change will compound these disasters, bringing shifting hurricane patterns, more intense droughts, and even worse floods. 

Preparing for ocean climate change

There is a lot we still don’t know about ENSO. Ultimately, we need better data to understand this phenomenon and to better predict how it will impact climate change — and vice versa. 

Part of the trouble in measuring the impact of ocean climate change on ENSO is that it’s difficult to pinpoint when an El Niño event begins. NOAA is currently tracking El Niño in real-time. Researchers have started to rely on ocean buoys to record different metrics that indicate when an El Niño event has started. 

For instance, ocean buoys track sea surface temperatures to get a more accurate reading of when an El Niño is happening.  An El Niño is declared when the average sea surface temperatures in the east-central tropical Pacific stay more than 0.5 degrees Celsius above the long-term average for five consecutive months. Sea surface height is also measured, as well as ocean color, surface winds, and cloudlines/precipitation.

However, still more data is needed to help humans prepare for more extreme or more frequent ENSO occurrences. Data can help inform flood maps, safely plan offshore aquaculture operations, and even enable the expansion of offshore wind farms that are resilient to La Niña and El Niño. Organizations must share data to provide the best possible forecast for the next ENSO event. 

El Niño and La Niña are difficult to track and predict, which makes it hard for scientists to pinpoint exactly how these phenomena will change with global warming. What we expect is for intense ENSO events to have a more significant impact on weather around the world. Therefore, the more data we can collect on this important pattern using technology like Sofar’s buoys — and by sharing information through Sofar’s API — the better prepared we will be in the future. 

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