Forecasters warn of record-breaking US summer heat amid intense El Niño

More than 100 million people could be affected in week leading to 4 July, with increased risks of droughts and wildfires

Meteorologists are anticipating a tumultuous summer that could rank as one of the US’s hottest ever.

New data released on Tuesday showed the first six months of the year were the hottest ever measured for parts of eight western states.

That data arrives as a potentially record-breaking heatwave is underway in the east. The National Weather Service expects temperatures over the 4 July holiday weekend to approach all time highs from Washington DC to New York with sweltering heat indexes topping 115F (46C).

This week’s intense heatwave will affect more than 100 million Americans and will be intensified by the growing influence of El Niño and a massive drought affecting 45 states . A similarly intense heatwave in recent days pushed temperatures to their highest-ever level in France, Germany and Denmark, resulting in hundreds of deaths across Europe .

Across the western US, numerous wildfires have broken – including in the mountains of Colorado where a dearth of winter snows remain after a record-warm start to the year.

“Our communities are feeling the firsthand impacts of severe drought and imminent fire danger,” Jared Polis, the Colorado governor, said at a wildfire briefing on Monday .

Local officials have been working for months to strengthen preparations for what is expected to be a brutal fire season. That includes sourcing additional equipment and working to free up additional federal support from the US Wildland Fire Service, a newly consolidated federal agency .

Last week, high temperatures were in the 90s in Seattle and Portland, Oregon – about 20F warmer than usual this time of year.

“We have known since April 1st that snowpack is very low across the western US,” said Guillaume Mauger, the state climatologist of Washington. “Knowing what to expect early on gives people time to prepare.”

Mauger cautioned that while there are many influences that will factor into this summer’s weather, the ongoing drought and a strengthening El Niño will continue to tilt the odds toward unusually warm temperatures. Research has tied low April snowpack to a higher risk of mountain wildfires across the entire intermountain west.

This year’s El Niño is taking place against a backdrop of particularly severe drought across the US, on par with the droughts of 1988 and 2012 that spawned enormous wildfires and blanketed the continent in sweltering smoke. It was the drought year of 1988 that saw weeks-long fires overwhelm Yellowstone national park, and fires in 2012 plagued California and Texas for months.

In the Colorado River basin, water levels are on pace for new record lows and have triggered new mandatory water restrictions affecting Nevada and Arizona . Later this summer, water levels could fall below critical thresholds needed to continue operating major hydropower dams along the river, including Hoover Dam.

Wildfires in Colorado and other western states have already begun sending persistent smoke plumes toward the midwest and eastern states, the latest episode in a worsening trend of poor summer air quality for the eastern two-thirds of the country .

Minnesota , Wisconsin and Michigan have already warned their residents about a heightened potential for unsafe air quality from wildfire smoke this summer. Last year, Madison, Wisconsin recorded some of the worst air quality in the country for an extended stretch of smoky days in July.

Extreme heat is the deadliest type of weather in the US in a typical year, but this year is shaping up to boost the risk even further, just as the country is welcoming more than a million international visitors for the World Cup.

This weekend’s World Cup matches could rank as the hottest ever played – surpassing even those held in Qatar in 2022. Fifa has instituted cooling breaks during this year’s World Cup matches for the first time.

Among vulnerable populations such as children, elderly people, or visitors unaccustomed with hot temperatures, the risk of injury or death during prolonged heat waves is even greater.

Regina Toto, a medical director of emergency preparedness at Children’s Hospital of Philadelphia, said her hospital has been planning for months along with local officials to respond to a potential mass casualty event due to a heatwave.

“As Philadelphia is one of the host cities for the World Cup, [we have] been part of several planning committees with municipal and healthcare partners to ensure preparedness of the overall healthcare infrastructure,” said Toto.

This year’s heat and fires are occurring as evidence is growing that human-caused climate crisis is accelerating – portending increased odds of tail-risk disasters. A rapid study conducted last week found that the European heatwave would have been “virtually impossible” without the influence of climate change.

The El Niño phenomenon, officially declared underway in June by the National Oceanic and Atmospheric Administration (Noaa), could be one of the strongest ever observed and is expected to boost global temperatures to new record highs over the next 12 to 18 months. El Niño works to liberate sub-surface heat stored in the Pacific Ocean, acting as an accelerant for global temperatures and a powerful influence on weather patterns worldwide.

In areas such as Philadelphia and Phoenix, which rely on air conditioning during intense summer heat, experts and government officials are growing concerned that a surge of electricity use by AI datacenters could increase the risk of a simultaneous mass blackout during a heatwave.

A 2023 study found that if a widespread blackout occurred during a stretch of record high temperatures in Phoenix, more than half of the city’s population could require hospitalization for heat-related illness or injury – with potentially tens of thousands of deaths.

“The appropriate focus right now is to hedge – prepare for possible impacts in case the worst of the forecasts come true,” said Mauger. “This is why early warnings are so valuable.”