A heat dome is expected to build over much of the U.S. this week, bringing scorching temperatures to the Midwest, Great Lakes, Ohio Valley, Mid‑Atlantic, and the South ahead of the fourth of July. At least 230 million people in the U.S.—about two-thirds of the country’s population are expected to be exposed to high temperatures.
It’s the latest heat wave in what is setting up to be a scorching summer in the U.S. and abroad. March through May 2026 ranked as the second-warmest spring in records going back to 1895 for the contiguous U.S., according to NOAA. With summer only just beginning, many might be wondering, how will it compare to past record hot years?
What are the three hottest years on record?
Globally, the last three years have all been among the hottest in recorded history. Beyond that, the last 11 years have all been among the hottest on record—in no small part due to climate change. The accumulation of heat-trapping greenhouse gases in our atmosphere are heating the planet at a rapid rate.
The warmest year since global records began in 1850 was 2024, by a wide margin. It was also an El Niño year—which is often associated with higher global average temperatures.
“The reason in that case was that there were three years of La Niña leading up to that El Niño event,” says Roundy. “Each one of those, although they cool the tropics, they warm the extratropics, the regions outside of the tropics. Then each La Niña event made the North Pacific warmer. Then El Niño hits, and El Niño warms the tropics and tends to cool the North Pacific.”
What are the hottest summers on record in the U.S.?
The summer of 2021 was one of the hottest on record in the U.S.—tying with the summer of 1936. June through August 2024 was the nation’s fourth-hottest summer on record, with Arizona, California, Florida, Maine, and New Hampshire all experiencing their warmest summer on record. Last year ranked as the 12th-warmest summer on record, according to NOAA.
How might this year compare?
With another El Niño here, experts say that this year will likely break global temperature records. This year is expected to be a “super El Niño”—a colloquial term for a particularly strong El Niño. Super El Niños can alter weather patterns for years and pose serious threats to ecosystems and human well-being. The last strong El Niño event, which took place in 2015, broughta record 16 tropical cyclones to the Northern Pacific and a 500-year drought in the Caribbean that led to water rationing in Puerto Rico, and marked 2015 as the hottest year on record. (It was quickly surpassed by 2016.)
“An El Niño event is going to result in a global increase in the surface temperature relative to the year before, and since climate change is trending the overall temperatures upward this just [adds to that.]”
However, some areas, including the central and eastern U.S., might see cooler—and wetter— than average temperatures as a result.
“The effect it has in North America is not very noticeable during the summertime, but as we head into the fall and into the wintertime, the effect is much, much greater,” says Zachary Johnson, a meteorologist and climate scientist.
In the northern hemisphere, a stronger El Niño tends to produce a warmer winter. Temperatures also continue to rise in the months after an El Niño reaches peak strength, meaning that 2027 is likely to be the hottest year in human history.
Yet, as the heat dome is proving, an El Niño year doesn’t mean you can expect a mild summer.
“If it was just El Niño acting, I would argue that eastern North America would be likely to experience fewer heat waves than we have experienced in recent years,” says Roundy. “But it isn’t just El Niño acting, and the next couple of weeks are likely to see some extreme temperatures in response to other [weather] phenomena.”
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