El Niño, one of the biggest contributors to last year’s record-breaking global temperatures, is nearly gone, and its opposite, La Niña, is on the way.
Whether this is a relief depends partly on where you live. Above-normal temperatures are still expected across the United States in summer 2024. Additionally, if you live on the Atlantic or Gulf coasts of the United States, La Niña can contribute to the worst possible combination of climate conditions that fuel hurricanes.
Pedro DiNezio, an atmospheric and oceanic scientist at the University of Colorado who studies El Niño and La Niña, explains why and what will happen in the future.
What is La Niña?
La Niña and El Niño are two extremes of a recurring climate pattern that can affect weather around the world.
Forecasters know that La Niña comes when temperatures in the eastern Pacific Ocean along the equator west of South America drop at least half a degree Celsius (0.9 Fahrenheit) below normal. During El Niño, the same region warms up.
These temperature fluctuations may seem small, but they can affect the atmosphere in ways that ripple across the planet.
In the tropics, there is an atmospheric circulation pattern called the Walker Circulation, named after Sir Gilbert Walker, an early 20th-century British physicist. The Walker Circulation is basically giant cycles of air rising and falling in different parts of the tropics.
Normally, air rises over the Amazon and Indonesia because moisture from tropical forests makes the air more lively there and descends into East Africa and the Eastern Pacific. During La Niña, these cycles intensify, creating stormier conditions where they rise and drier conditions where they descend. During El Niño, ocean heat in the eastern Pacific shifts these cycles, so the eastern Pacific becomes even stormier.
EL Niño and La Niña also affect the jet stream, a strong air current that blows from west to east across the United States and other mid-latitude regions.
During El Niño, the jet stream pushes storms into the subtropics, making these typically dry regions wetter. Conversely, mid-latitude regions where storms would normally occur become drier as storms change direction.
Forecasters expect a rapid transition to La Niña this year; probably towards the end of summer. Following the strong El Niño the world saw in late 2023 and early 2024, conditions tend to revert to La Niña fairly quickly. How long it will last is an open question. This cycle tends to change from extreme to extreme every three to seven years on average, but El Niños tend to be short-lived while La Niñas can last two years or longer.
How does La Niña affect hurricanes?
Temperatures in the tropical Pacific also control wind shear over large parts of the Atlantic Ocean.
Wind shear is the difference in wind speeds at different elevations or directions. Hurricanes have a harder time holding column structures during strong wind shear because stronger winds push the columns apart at higher altitudes.
La Niña produces less wind shear, eliminating the brakes on hurricanes. This isn’t good news for people living in hurricane-prone areas like Florida. In 2020, the Atlantic saw a record 30 tropical storms and 14 hurricanes during the latest La Niña; In 2021, there were 21 tropical storms and seven hurricanes.
Forecasters are already warning that this year’s Atlantic storm season could rival 2021, largely due to La Niña. The tropical Atlantic was also extremely warm, breaking sea surface temperature records for more than a year. This heat affects the atmosphere, causing more atmospheric movement over the Atlantic, fueling hurricanes.
Does La Niña mean drought is returning to the US Southwest?
Water supplies in the southwestern United States will likely be in good shape during the first year of La Niña due to last winter’s rains. But the second year tends to be problematic. A third year could lead to severe water shortages, as the region sees in 2022.
Drier conditions also fuel more extreme fire seasons in the West, especially in the fall when winds pick up.
What happens in the Southern Hemisphere during La Niña?
The effects of El Niño and La Niña are almost a mirror image in the Southern Hemisphere.
Chile and Argentina tend to experience drought during La Niña, while the same phase leads to more rain in the Amazon. Australia experienced severe flooding during the last La Niña. La Niña also favors the Indian monsoon, which means above-average rainfall. However, the effects are not immediate. In South Asia, for example, changes often occur several months after La Niña officially emerges.
La Niña is particularly bad for East Africa, where vulnerable communities are already in a long-term drought.
Does climate change affect the impact of La Niña?
El Niño and La Niña are now experienced due to the effects of global warming. This could worsen temperatures and precipitation out of normal, as the world sees in 2023.
Since the summer of 2023, the world has experienced 10 months of record-breaking global temperatures. Much of this heat comes from the oceans, which are still experiencing record high temperatures.
La Niña is supposed to cool things down a bit, but greenhouse gas emissions that cause global warming are still rising in the background. Therefore, although the fluctuations between El Niño and La Niña cause short-term temperature fluctuations, the general trend is that the world is warming.
This article is republished from The Conversation, an independent, nonprofit news organization providing facts and analysis to help you understand our complex world.
Written by: Pedro DiNezio, University of Colorado Boulder.
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Pedro DiNezio receives funding from NSF.