Scientists change how El Nino is labeled to keep up with spike in
temperature
[February 21, 2026]
By SETH BORENSTEIN
WASHINGTON (AP) — The natural El Nino cycle, which warps weather
worldwide, is both adding to and shaped by a warming world,
meteorologists said.
A new study calculated that an unusual recent twist in the warming and
cooling cycle that includes El Nino and its counterpart La Nina can help
explain the scientific mystery of why Earth's already rising temperature
spiked to a new level over the past three years.
Separately, scientists have had to update how they label El Nino and La
Nina because of rapid weather changes cause by global warming.
Increasingly hot waters globally have caused the U.S. National Oceanic
and Atmospheric Administration this month to alter how it calculates
when the weather pattern has flipped into a new cycle. It's likely to
mean that more events will be considered La Nina and fewer qualify as an
El Nino for warming tropical waters.
Earth's average monthly temperature took a noticeable jump up from the
long-term upward trend connected to human-caused climate change in early
2023, and that increase continued through 2025. Scientists have many
theories about what's happening, including an acceleration of greenhouse
gas warming, a reduction in particle pollution from ships, an underwater
volcano eruption and increased solar output.
In a new study in Nature Geoscience this month, Japanese researchers
look at how the difference in energy coming to and leaving the planet —
called Earth's energy imbalance — increased in 2022. An increased
imbalance, or more trapped heat, then leads to warmer temperatures,
scientists said. The researchers calculate that about three-quarters of
the change in Earth's energy imbalance can be attributed to the
combination of long-term human-caused climate change and a shift from a
three-year cooling La Nina cycle to a warm El Nino one.
What's El Nino vs. La Nina
El Nino is a cyclical and natural warming of patches of the equatorial
Pacific that then alters the world's weather patterns, while La Nina is
marked by cooler than average waters.
Both shift precipitation and temperature patterns, but in different
ways. El Ninos tend to increase global temperatures and La Ninas depress
the long-term rise.
La Ninas tend to cause more damage in the United States because of
increased hurricane activity and drought, studies have shown.
Why weather cycles switch from warm to cool
From 2020 to 2023, Earth had an unusual “triple dip” La Nina without an
El Nino in between. In a La Nina, warm water sticks to a deeper depth,
resulting in a cooler surface. And that reduces how much energy goes out
into space, said study co-author Yu Kosaka, a climate scientist at the
University of Tokyo.
She compared it to what happens when people have fevers.
“If our body's temperature is high then it tends to emit its energy out,
and the Earth has the same situation happening. And as the temperatures
increase, it acts to emit more energy outward. And for three-year La
Nina, it’s opposite,” Kosaka said.
So more energy — which becomes heat — is trapped on Earth, she said. La
Ninas more typically correspond to a one- or two-year buildup of extra
energy imbalance, but this time it was longer so the difference was more
noticeable and included hotter temperatures, Kosaka said.
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A man carries usable belongings salvaged from his flood-hit home
across a flooded area in Shikarpur district of Sindh province, of
Pakistan, Wednesday, Aug. 31, 2022. (AP Photo/Fareed Khan, File)
 “When there is a transition from La
Nina to El Nino, it's like the lid is popped off,” releasing the
heat, explained former NOAA meteorologist Tom Di Liberto, who's now
with Climate Central.
About 23% of the energy imbalance driving the recent higher
temperatures comes from this unusually long La Nina pattern, with
slightly more than half coming from gases from the burning of coal,
oil and gas, the study authors said. The rest can be other factors.
Scientist Jennifer Francis of the Woodwell Climate Research Center,
which wasn't involved in the study, said the research makes sense
and explains an increase in energy imbalance that some scientists
were attributing to accelerated warming.
Changing how El Ninos and La Ninas are labeled
For 75 years when meteorologists calculated El Ninos and La Ninas,
it was based on the difference in temperature in three tropical
Pacific regions compared to normal. An El Nino was 0.5 degrees
Celsius (0.9 degrees Fahrenheit) warmer than normal and La Nina was
cooler than normal by the same amount.
The trouble in a warming world is what's considered normal keeps
shifting.
Until now, NOAA used the 30-year average as normal. It updated the
30-year average every decade, which is how often it updates most
climate and weather measurements. Then the water warmed so much for
El Ninos and La Ninas that NOAA updated its definition of normal
every five years, but that wasn't enough either, said Nat Johnson, a
meteorologist at NOAA's Geophysical Fluid Dynamics Lab.
So NOAA came up with an El Nino index that's relative, starting this
month. This new index compares temperatures to the rest of Earth's
tropics. Recently that difference between the old and new methods
has been as much as half a degree Celsius (0.9 degrees Fahrenheit),
and “that's enough to have an impact,” Johnson said.
That's because what really matters with El Ninos and La Ninas is the
way the waters interact with the atmosphere. And recently the
interactions didn't match the old labeling, but they do match the
new method, Johnson said.
This will likely mean a bit more La Ninas and fewer El Ninos than in
the old system, Johnson said.
Here comes another El Nino
NOAA's forecast is for an El Nino to develop later this year in the
late summer or fall. If it comes early enough, it could dampen
Atlantic hurricane activity. But it would also mean warmer global
temperatures in 2027.
“When El Nino develops, we’re likely to set a new global temperature
record,” Woodwell's Francis said in an email. “'Normal' was left in
the dust decades ago. And with this much heat in the system,
everyone should buckle up for the extreme weather it will fuel.”
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