Climate Effects of El Niño and La Niña

Predicting global weather patterns is essential for forecasting extreme weather events, agricultural planning, and safeguarding the world’s population from natural disasters. Two of the biggest factors contributing to global weather changes are El Niño and La Niña. These terms refer to changes in the patterns of winds, ocean currents, and water temperatures observed in the Pacific Ocean, which in turn have global effects on the Earth’s weather systems.  

Is it El Niño or La Niña? 

The factors that dictate El Niño (full name El Niño-Southern Oscillation or ENSO) are complex and require the global input and collaboration of oceanographers, geographers, atmospheric scientists, and researchers in a variety of other fields to predict. Put simply, if the temperatures in the Equatorial Pacific Ocean are warmer than usual, we will experience El Niño; if they are colder than usual, La Niña will occur.  

The National Oceanic and Atmospheric Administration (NOAA) has observed continued La Niña conditions since September 2020. The Administration’s Climate Prediction Center (CPC) estimates a 52% chance that it will endure until September 2022 and a slightly lower chance through the end of the year. While La Niña can last anywhere from one to three years, a three-year La Niña is unusual and has only been observed twice since 1950.  

What are the effects? 

Many observed effects of ENSO depend on the phase it is in. One of the main observed effects is the increase in intensity and frequency of hurricanes in either the Atlantic or Pacific Ocean, depending on the phase. During El Niño, hurricane frequency increases in the Pacific, affecting the West Coast of the United States and Mexico; during La Niña, more hurricanes are observed in the Atlantic Ocean, which can have serious effects on nations in the Caribbean as well as the Southeast United States.  

Precipitation across the United States is also affected. During El Niño, precipitation increases dramatically at lower latitudes, meaning more rain will occur in places like Southern California and the South and Southeast. When La Niña occurs, there is higher than average precipitation further north (Pacific Northwest, Rocky Mountains, Northern California) and in the Midwest, and less in the Southern regions. This is one reason why there are more hurricanes during La Niña, as less precipitation allows for them to form more frequently. Combined with warmer Atlantic waters and weaker winds that would typically work to break up stronger storms, we observe hurricanes with more intensity and more often during La Niña. 

United States residents are particularly concerned whether the patterns indicate El Niño or La Niña as it can have crucial effects on the strength of hurricanes in the Southeast, as well as unseasonably high or low temperatures throughout the country. Hurricane Ida, the second-most damaging hurricane to the State of Louisiana, occurred during La Niña, due to its ability to increase tropical storm intensity.  

Globally, ENSO affects nearly all of the world’s weather patterns and can have devastating effects. During El Niño, heavy rains affect East Africa, South Asia, and parts of South America. From a public health perspective, El Niño affects the cycle of epidemic diseases, especially malaria in countries like Colombia and India. 

In the La Niña phase, drought is more commonly observed in South American regions like Peru and Chile, while wetter seasons can take place in Brazil. Record-breaking snows can occur in Canada during times of La Niña as well.  

Are there climate change implications? 

It is challenging for scientists to conclude whether or not the patterns of ENSO will be affected by climate change. NOAA has observed the magnitude of ENSO phase swings to have increased, but that does not allow them to conclude that this is beyond the normal behavior of El  Niño / La  Niña. Other modeling claims to have predicted that human-induced warming of the oceans can lead to variations in the phases of ENSO,, along with changes in rainfall responses, although these models are unable to predict anything much more specific than that. Generally, the scientific community does not know how the warming of the climate will affect El Niño/La Niña, when changes will occur, or how dramatic these changes will be with the current understanding of ENSO. 

What is clear is that ENSO is responsible for wide swings in the globally observed climate. For instance, the current drought in the Southwest US has brought the water levels of Lake Mead, which provides water for millions of residents across the West, to critically low levels. In tandem with other factors, this is one of the effects of La Niña in action. Should historical trends hold, these areas should experience an increase in water levels when El Niño comes back, which could help to replenish these reserves.