Climate Matters•February 8, 2023
El Niño and La Niña: Local and global effects
Since 2020, the planet has been in a cold phase (La Niña) of the El Niño-Southern Oscillation (ENSO) climate pattern. But that’s about to change.
Heading into spring 2023, we’re approaching a likely transition from La Niña to the neutral phase of ENSO.
The ENSO state has a major influence on weather patterns across the globe—including in the U.S.
The warm phase (El Niño) can boost global temperatures, layering the warm ENSO phase on top of the primary long-term warming trend due to carbon pollution.
The ongoing La Niña winter is the third in a row—a rare three-peat that’s likely to end soon. According to NOAA, there’s an 82% chance of a shift from La Niña to the neutral phase as we head into spring.
Both phases are part of the El Niño-Southern Oscillation (ENSO)—the most influential natural climate pattern influencing year-to-year weather conditions across the globe.
What is ENSO?
ENSO includes warm (El Niño), cold (La Niña), and neutral phases:
Neutral: Easterly trade winds cause deep, relatively cool, nutrient-rich waters to rise to the surface along the coast of Peru and along the equator. Tropical Pacific sea surface temperatures are within +/- 0.9°F of normal.
El Niño: Easterly trade winds weaken. Upwelling ocean currents along the coast of Peru and along the equator weaken. Surface waters in the tropical Pacific are warmer than normal.
La Niña: Easterly trade winds strengthen. Strong upwelling of cold ocean currents along the equator and coast of Peru keeps warm surface waters in the western Pacific. Surface waters in the tropical Pacific are cooler than normal.
Every two to seven years, sea surface temperatures in the tropical Pacific Ocean flip between warmer than average (El Niño) and colder than average (La Niña) phases (pausing in the neutral phase between).
The ENSO state directly affects temperature, rainfall, and wind patterns across the tropics—and has cascading indirect effects at a global scale.
ENSO’s global reach
During each ENSO phase, the position of warm surface water and associated areas of rising moist air masses shifts from the western Pacific (during La Niña) to the central and eastern Pacific (during El Niño).
This periodic re-positioning of warm water and convective air across the vast equatorial Pacific Ocean disrupts other large-scale atmospheric circulation patterns that move heat and moisture from the tropics toward the mid-latitudes.
When it interferes with the mid-latitude jet streams, ENSO can affect temperature and precipitation in regions far from the tropical Pacific.
The effects of each ENSO event vary based on the event’s intensity and timing, but NOAA’s diagrams summarize general effects on temperature and rainfall at a global scale for:
La Niña: including wet conditions in Australia and Indonesia, raising risks of flooding
El Niño: including dry drought- and wildfire-prone conditions in Australia and Indonesia
This is how ENSO influences the likelihood, timing, and location of drought, floods, extreme heat, and other weather patterns that are integral to rainfed agriculture, fisheries, freshwater resources, and public health—in the U.S. and around the world.
ENSO’s ripple effects in the U.S.
In the U.S., ENSO is generally associated with:
La Niña events in the tropical Pacific can shift the jet stream to the north, causing warm and dry winters across the southern U.S. and wetter and cooler conditions in the Pacific Northwest and Alaska.
El Niño events are associated with cool and wet winters along the southern U.S., and with mild winters in Alaska and Northwest Canada.
La Niña generally reduces hurricane activity in the Pacific and enhances it in the Atlantic. La Niña leads to less wind shear in the tropical Atlantic, making it easier for hurricanes to form.
The reverse is true for El Niño.
There’s also emerging evidence linking:
La Niña to more frequent tornadoes in the southeast, and
El Niño to more frequent atmospheric rivers on the West Coast.
ENSO and global temperatures
Carbon pollution from human activities has caused a long-term rise in global temperatures. Natural factors—including the year-to-year ENSO status—can nudge global temperatures up or down slightly relative to this long-term, human-caused trend.
Despite the global cooling effect of the persistent La Niña, 2022 was still the planet's sixth hottest year (regionally, 2022 was the second-hottest year on record for both Asia and Europe).
The consecutive La Niña years of 2022 and 2021 both rank among the top 10 hottest years on record—all of which have occurred since 2010. This suggests that the short-lived global cooling effect of La Niña has not been enough to even briefly mask human-caused warming.
With La Niña forecasted to fade by spring, 2023 will almost certainly be warmer than 2022.
The strong El Niño event of 2015-2016 likely gave a boost to 2016’s ranking as the hottest year on record—and demonstrates the serious global consequences of such events.
During the 2015-2016 El Niño, Indonesia suffered from widespread forest fires while Peru experienced catastrophic flooding and coral bleaching events were reported in the warmer-than-normal Pacific Ocean. At the time, the World Health Organization estimated that 60 million people across Africa, Latin America and the Caribbean, and the Asia-Pacific region were impacted by drought, heat and rainfall extremes, and associated food insecurity and disease outbreaks (consistent with a 2019 study).
LOCAL STORY ANGLES
What are some other impacts of ENSO in your region?
NOAA’s most requested El Niño and La Niña images include visual summaries of a range of ENSO-related impacts in the U.S. View U.S. temperature and precipitation during every El Niño since 1950; or U.S. temperature and precipitation during every La Niña since 1950. Explore the impacts of ENSO on U.S. hurricanes and tornadoes and hailstorms. NOAA’s Regional Climate Centers may provide reports and resources on regional ENSO impacts, for example from the High Plains Regional Climate Center and the Midwestern Regional Climate Center.
Where is the latest ENSO outlook?
NOAA’s Climate Prediction Center releases an official ENSO status update on the second Thursday of every month. Learn about the criteria used by NOAA to determine current ENSO status here. NOAA’s National Centers for Environmental Information also monitors current ENSO conditions, and provides access to long-term records of several ENSO indicators. Climate.gov’s ENSO hub and ENSO blog compile the latest outlooks and an array of resources for learning about ENSO and its impacts. Columbia University’s International Research Institute for Climate and Society’s comprehensive ENSO Resources page provides regular ENSO forecasts and related news and resources.
Michelle L'Heureux (available for print/phone interviews only)
NOAA Climate Prediction Center
Relevant expertise: ENSO, subseasonal-to-seasonal climate variability and prediction
Media Contact: Allison Santorelli (Allison.Santorelli@noaa.gov)
Assaf Anyamba, PhD
Distinguished R&D Staff Member and Group Lead
National Security Sciences Directorate
Oak Ridge National Laboratory
Relevant expertise: Disease outbreaks associated with ENSO events
Contact: Eric Swanson (firstname.lastname@example.org)
Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts.
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We analyzed the relationship between global mean temperatures measured by NASA and ENSO state determined by temperatures in the eastern tropical Pacific. Focusing on data since 1950 (when ENSO data becomes reliable), we first looked at how to characterize the long-term trend in global mean temperature. We found that a function that allowed for curvature was the best fit to this data (R^2 = 0.92, p<0.01). This is consistent with global warming related to rising carbon dioxide levels. We then subtracted this curve from the global mean data. This new data set is the departure from what we would expect based on the global warming trend. We then asked whether ENSO conditions explain these departures. We found that ENSO had a delayed effect, with the average ENSO value from September through August having the closest relationship to annual (January through December) global mean temperature (R^2 = 0.38, p<0.01).