This heat wave would be ‘virtually impossible’ if not for fossil fuel pollution, study says

By Meteorologists Briana Waxman, Mary Gilbert, with Kate Petersen reporting

(CNN) — The dangerous, multi-day heat wave is tightening its grip on the eastern US, shattering records, straining the electric grid and raising the risk for millions of people preparing to celebrate the Fourth of July outdoors. And human-caused climate change is making the familiar summer weather pattern far more dangerous.

The heat wave was triggered by the strong heat dome parked over the Northeast — a stagnant area of high pressure that traps and enhances hot, humid air.

But the intensity of the heat and humidity combined this week would have been “virtually impossible” without the effects of fossil fuel pollution. The finding was published early Friday from World Weather Attribution, a scientific network which analyzes the role of climate change in driving extreme weather events.

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“When a historic 4th of July celebration is disrupted, and World Cup matches are played in conditions that are unsafe for players and fans, it shouldn’t take another scientific study to wake people up,” said Friederike Otto, a professor of climate science at Imperial College London. “Climate change is here, it’s already impacting the things we enjoy in our everyday lives, and it will continue to get worse the longer we drag out the inevitable transition to net zero emissions.”

The worst of the heat is here Friday, after at least 20 locations broke or tied daily temperature records Thursday. As homes and businesses crank up air conditioning to stay cool, demand for electricity is surging in the Mid-Atlantic and Northeast, where heat and humidity are pushing conditions into dangerous territory.

Washington, DC, Philadelphia, New York City and Boston are all forecast to see highs near or above 100 degrees Friday. The combination of heat and humidity will make conditions feel even hotter, with heat index values — what the air actually “feels like” to the body — forecast to climb as high as 107 degrees in Washington and New York City, 110 in Philadelphia and 106 in Boston.

The brutal heat continues Saturday for DC, which is forecast to remain near 103 degrees with a heat index up to 108. Philadelphia could reach 101 with a heat index up to 106. New York City is expected to hit 97 and Boston is forecast to top out near 95 degrees Saturday.

Heat is the deadliest weather hazard in the US, and the high humidity increases the risk, keeping temperatures elevated and preventing sweat from evaporating efficiently, making it harder for the body to cool itself. Overnight lows are also hotter now than they were decades ago, making it harder for people to get respite and rest.

The risk can build quickly, especially for older adults, children, outdoor workers and people without reliable access to air conditioning. Anyone heading outside for the holiday weekend should plan for frequent breaks indoors or at least in the shade. Drink water often, avoid intense activities and never leave children or pets in parked cars.

Heat strains power grid

Energy Secretary Chris Wright directed data centers in the mid-Atlantic this week to use their backup power supplies instead of using electricity from the public grid, in part to ensure there was enough to power residential air conditioning.

Wright’s Tuesday orders were directed at data centers and other large electricity customers served by PJM, the country’s largest electrical grid operator. The PJM region is made up of 13 states. It is home to the world’s largest cluster of data centers in Virginia, and their dramatic energy use has led to serious electricity price spikes in certain mid-Atlantic states over the past couple years.

Outside of the PJM grid, more than 19,000 Con Edison customers in the New York City metro area and stretching upstate lost power Thursday, according to the utility’s outage map. Con Edison said Thursday it is reducing voltage for parts of the Bronx and Manhattan to conserve energy during equipment repairs, and is asking customers to limit the use of air conditioners and energy-intensive appliances.

Mayor Zohran Mamdani posted on X to ask residents to set their AC to 78 degrees and unplug appliances to help conserve electricity and reduce the load on the grid.

Managing the holiday heat

Many cities, including Boston, New York, Philadelphia, Washington, DC, and Raleigh, North Carolina, are opening cooling centers and expanding public resources as the dangerous heat settles in.

Washington, DC, has activated an extreme heat alert through July 5 and is expanding cooling centers, hydration stations and emergency medical resources as hundreds of thousands of visitors descend on the nation’s capital for holiday events.

Organizers of National Mall celebrations are adding water stations, cooling tents and air-conditioned buses for attendees. Thursday night’s public rehearsal for PBS’s annual “A Capitol Fourth” concert has been canceled due to the excessive heat, the US Capitol Police said in a news release. Organizers will announce by 10 a.m. Friday whether the concert itself will be canceled.

New York City opened hundreds of cooling centers and deployed mobile medical vans to provide water, sunscreen and wellness checks. More than 2,200 LinkNYC kiosks are displaying directions to the nearest cooling center.

Philadelphia has declared a heat health emergency through Saturday evening and shortened the route for its Fourth of July parade. A ceremony featuring a live virtual address from the pope has been moved indoors, and officials have reduced hours for the city’s World Cup fan festival ahead of Saturday’s match between Paraguay and France. Event organizers have also canceled Fourth of July and World Cup block parties.

Just outside of Philadelphia, Norristown, Pennsylvania, and Haddon Township, New Jersey, have also both canceled Fourth of July parades due to the heat.

The searing temperatures could also impact air travel: Delta Air Lines has issued a high heat advisory for New York’s LaGuardia Airport through July 4 “due to hot weather compounding with operational constraints.”

Amtrak has also warned that trains may see delays through July 4 if they have to run at reduced speeds due to the intense heat across the Northeast, Southeast and Midwest.

Some relief is expected to begin arriving across parts of the Midwest later in the holiday weekend before gradually spreading into portions of the Northeast. Much of the South, however, is expected to remain hotter than normal into next week.

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CNN’s Kate S. Peterson, Andrew Freedman and CNN Meteorologists Mary Gilbert and Chris Dolce contributed to this report.