As extreme heat smothered the eastern United States over the July Fourth weekend and Europe struggled with its own deadly heat wave, experts warned that more record high temperatures could be in store for this year because of a strengthening El Niño.
“We know that temperatures are warming in the long term, linked to human-caused climate change, and El Niño acts to boost those temperatures temporarily,” climate scientist Zachary Labe of the nonprofit Climate Central said in a recent briefing.
Between June 2025 and April, Labe said, global average surface temperatures were about 1.8 to 2.7 degrees above pre-Industrial Revolution levels. But an average of forecast models suggests global average surface temperatures could be even higher in the winter — perhaps hitting 3.24 to 3.42 degrees above the pre-Industrial Revolution era.
“This would indicate a very high likelihood that we will be breaking new global temperature records in just a few months,” Labe said.
While California escaped oppressive heat conditions this weekend, officials issued a heat advisory for Tuesday through Thursday, when temperatures could hit 90 to 103 degrees across inland areas of Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties.
Beyond California, scientists are raising alarms over the planet’s warming oceans, which — coupled with a strong El Niño — could increase temperatures for land dwellers in the coming weeks.
On Wednesday, officials confirmed that the global sea surface temperature in June hit a record for this time of year.
“Current conditions could indicate the beginning of a new phase, leading, once more, to uncharted territory. With ocean temperatures at these levels and El Niño on the horizon, we are likely to see more temperature records fall in the coming months,” said Carlo Buontempo, director of the Copernicus Climate Change Service, an arm of the European Union.
Warming ocean waters have wide-ranging effects, scientists say. They can provide extra energy to storms and increase evaporation, boosting the chance for extreme precipitation and flooding; contribute to sea level rise; exacerbate ice melt and stress marine ecosystems, according to a statement from the Copernicus Climate Change Service and Copernicus Marine Service.
Federal officials last month officially declared the arrival of El Niño, and said there was an 88% chance that the climate pattern would be either “strong” or “very strong” by the end of the year.
El Niño describes a pattern characterized by warmer water in the central and eastern tropical Pacific Ocean. The effect enhances a weakening of the typical east-to-west trade winds, allowing even more warm water to pool in that area of the ocean, reaching the coast of Mexico, Central America and northern South America — as well as coastal Southern California.
Typically, El Niño is associated with wetter-than-normal conditions during the winter in Southern California. Of the last four “very strong” El Niños in the global record, three — 1982-83, 1991-92 and 1997-98 — brought above-average rain to Southern California.
El Niño is expected to prolong an existing unrelated marine heat wave that would otherwise typically start fading between October and December, scientists say. Such a prolonged period of higher-than-normal ocean temperatures can wreak havoc on wildlife.
A map of two marine heat waves — currently unrelated to El Niño — off the California coast and farther west in the Pacific Ocean.
(National Oceanic and Atmospheric Administration)
Much of the U.S. is already baking under searing heat — even though El Niño is not yet in full force.
An extreme heat warning was in effect through Independence Day weekend across portions of the Midwest, South and Northeast, with New York City‘s Central Park reaching 100 on Thursday, the hottest temperature recorded there since July 18, 2012.
The story is much the same in other areas of the world.
Europe has baked under a historic, extraordinary heat wave recently, according to the World Meteorological Organization, with Germany breaking all-time temperature records and nights bringing little relief.
“Extreme heat is one of the most serious and rapidly growing threats to health and safety posed by climate change,” Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, said in June. “It claims around half a million lives globally each year, yet many of these deaths are preventable.”
More than 1,300 excess deaths recorded for the week that ended June 28 were linked to high temperatures in Europe, according to Tedros.
“Driven by climate change and global warming, the phenomenon of the ‘once-in-a-generation’ heatwave is now occurring nearly [annually],” he wrote on X. “We were warned.”
In general, the global average temperature has already increased by 1.8 degrees, or 1 degree Celsius, since the preindustrial period, according to NASA, and is increasing by more than 0.36 degrees per decade. Global climate change — which is exacerbated by human activities such as the burning of fossil fuels — is expected to increase U.S. sea levels, cause hurricanes to become stronger and more intense, decrease water supplies in the West and Southeast, contribute to more-intense droughts and heat waves, and extend and intensify wildfire season.
Areas of France, Britain, Austria and the Netherlands have issued red alerts or warnings on account of the extreme heat. According to the Associated Press, Berlin police used water cannons — normally used to disperse protesters — to cool down cheering crowds in front of the Brandenburg Gate. It’s so hot in Germany, the AP said, that the concrete on highways is breaking up, and officials urged people to avoid unnecessary train travel.
The temperatures were so hot in France that the lack of air conditioning in many parts of hospitals is posing a health risk. One hospital had rooms that were so hot patients needed to be moved to an air-conditioned waiting room, Reuters reported.
The heat has become so unbearable in Japan that weather officials in April announced a new term for days when maximum temperatures exceed 104 degrees — kokushobi, meaning harsh or cruel heat, according to the Japan Times.
In Taiwan, extreme heat has prompted officials to simulate a disaster scenario involving three consecutive days of temperatures hitting 104 degrees, power outages, heat illnesses, deformed roads, garbage fires and a forced reduction in railway speeds, according to the island’s Central News Agency.
Japan and Hong Kong reported their second-warmest springs on record, Africa had its fourth-warmest May on record and extreme heat in India and Pakistan has become deadly, with temperatures exceeding 113 degrees in many spots, the National Centers for Environmental Information said. The Arctic Ocean also saw its second-lowest sea ice extent for the month of May.
To prepare California for more periods of extreme heat, the state now has a tool, CalHeatScore, that offers an “extreme heat scoring system” with five numerical levels. The tool also offers people a list of resources like cooling centers.
Los Angeles County also now posts heat-related emergency room visits on an online dashboard.
“When temperatures rise, the body can lose its ability to cool itself, leading to heat-related illnesses such as heat exhaustion, heat stroke, heat cramps and heat rash, and making heart, lung, brain and other health conditions worse,” the L.A. County Department of Public Health said.
“Nationally, extreme heat is the leading cause of weather-related deaths in the United States, surpassing floods, hurricanes, and tornadoes combined.”
