More than 160 million people in the U.S. are under extreme heat warnings or advisories as global oceans reach new record sea-surface temperatures. Climate and disaster-preparedness experts stress that the heat is already reshaping weather, climate, and marine
By June 30, the map of danger is already plastered across the U.S. in purple—extreme heat warnings stretching over entire states including Illinois, Indiana, Kentucky, and Ohio.
This year’s heat is not only a matter of discomfort. Right now, more than 160 million people across the country are under extreme heat warnings or advisories, with dangerous conditions spreading alongside a broader global pattern that researchers say is intensifying.
The timeline starts with the oceans. On June 21—the first day of summer—global sea surface temperatures outside the polar regions exceeded record levels set in 2023 and 2024. according to the Copernicus Climate Change Service and the Copernicus Marine Service. The agencies said the increase was anticipated with El Niño conditions. but they also warned that the ocean’s new record was expected to have “consequences for both weather patterns. global climate and marine ecosystems. ” a warning echoed in a press release jointly issued on July 1.
Those ocean temperatures matter because they feed the system that people experience on the ground: hot air. sticky nights. and conditions that are harder to recover from. For many Americans, the risk is not theoretical. It is the difference between staying safe overnight and becoming one of the people heat illness catches when the body can’t cool down.
The American Red Cross has offered straightforward steps for that reality—what to do before extreme heat arrives, and what to do while it is happening. The guidance begins with hydration and simple restraint: stay hydrated and avoid caffeinated, sugary and alcoholic drinks.
It also asks people to prepare like emergencies can arrive fast. Gather emergency supplies such as water, medicine and sunscreen. Make a plan to stay cool—spend time in air-conditioned places and wear lightweight, breathable clothing.
Heat safety isn’t just about prevention; it’s also about recognition. Learn emergency skills, such as first aid and CPR, and recognize the signs of heat illness.
And because extreme heat can isolate people who need help, the Red Cross also emphasizes staying connected. Check on friends, family and neighbors. Sign up for free emergency alerts from your local government.
A recurring theme is how heat behaves differently across the world. sometimes in ways that surprise even people trying to follow the numbers. Internationally. Columbia Climate School reporting has highlighted repeated heat-wave “hotspots” appearing across the globe—distinct regions seeing extreme heat so severe they cannot be explained by climate models. Another study discussed in that coverage found that high heat was preferentially killing the young. not the old: mortality research in Mexico pointed to young adults and small children as the main victims of extreme heat.
In the same thread of warnings about what happens when heat crosses thresholds humans can survive only with cooling. there is also the prospect that large areas could face possibly fatal heat waves if warming continues—so severe that even healthy young adults may not be able to survive without access to artificial cooling.
In New York City, the risk has a different face: heat that comes from infrastructure and daily life. A viewpoint on how to fix the “hellish heat” of the New York City Subway System argued that subway heat should be treated as a climate adaptation issue and a public health hazard.
Experts tie the current heat conditions to humidity as well as temperature. In coverage tied to the July 1 weekend. Columbia Climate School professor Radley Horton said the heat wave’s defining feature has been especially high humidity. “When the amount of moisture in the air is particularly high, it tends to make nights that much warmer. Temperatures don’t change as much between daytime and nighttime.”.
That matters because nights are supposed to be when the body gets relief. When that cooling fails, the danger accumulates—heat becomes something your system has to carry into the next day.
Disaster preparedness specialists are also focusing on the practical burden heat can place on large crowds. With the FIFA World Cup 2026 in full swing in Canada, Mexico and the U.S., Joshua L. DeVincenzo—National Center for Disaster Preparedness expert at Columbia Climate School—shared heat-safety tips aimed at protecting the health of fans and players.
For Americans, there is another pressure point beneath the health advice: the cost of staying cool. Aging infrastructure is cited as a top reason some Americans are facing electricity cost increases substantially. Alexis Abramson. Columbia Climate School Dean and sustainable energy technology expert. said that maintenance and upgrades to the electricity grid have long been deferred. and that new transmission lines and significant distribution upgrades are needed. She added that utilities are passing modernization expenses directly to ratepayers.
Across the Atlantic, the financial consequences are showing up in income and household stability. Extreme heat and drought have cut average household incomes across Europe. putting millions at risk of poverty. according to a study discussed in Bloomberg coverage. Climate economist Gernot Wagner of Columbia Business School said research is now able to pinpoint these costs more clearly as climate change accelerates. “The compounding effects over time are big enough that they do already show up in economic statistics. We are already poorer because of climate change,” he said.
Europe is also dealing with the temperature itself. The data shows the continent is the fastest-warming on Earth, and in the U.K. and France the current heat wave has been breaking records. In one interview round, Columbia University professor Radley M. Horton discussed the challenges surrounding climate change in Europe. In another. Columbia Climate School professor and National Center for Disaster Preparedness faculty director Jeff Schlegelmilch spoke about short- and longer-term preparedness as Paris recorded its hottest June day on record.
All of these threads—record ocean temperatures, hotter nights, guidance for basic survival, and the costs of cooling—connect to one immediate question: what comes next for the months ahead when the heat doesn’t let up after the first wave.
For now, the steps are clear and urgent. Hydrate. prepare supplies like water. medicine and sunscreen. plan time in air-conditioned places. recognize the signs of heat illness. learn first aid and CPR. and keep checking on each other. When the danger stretches over entire states and touches more than 160 million people. preparation stops being advice and becomes the difference between coping and crisis.
extreme heat heat wave sea surface temperature Copernicus El Niño heat illness American Red Cross Radley Horton disaster preparedness climate adaptation