"Heat dome" conditions -- in which high-pressure systems trap warm air like the lid on a pot -- persisted over the Midwest and South and were moving east, with some 46 million people under heat alerts."We are entering what could be the most extreme heat wave this city has seen in over a decade," New York Mayor Zohran Mamdani said in a video, adding he wanted people to stay safe while watching the World Cup, celebrating the Fourth of July or -- he joked -- "renting out MSG to get married, hypothetically."Pop superstar Taylor Swift is rumored to have rented Manhattan's famed Madison Square Garden venue for her wedding to American football star Travis Kelce.New York has designated hundreds of public buildings as cooling centers, extended public swimming pool hours, dispatched volunteers to check on vulnerable residents, and opened "pop up" cooling stations with misting fans and wet towels.In the Midwestern city of Chicago, the energy grid was under "critical strain," utility ComEd said as air conditioning usage surged."Raise your thermostat as high as is comfortably safe," the company urged, while calling on residents to delay using laundry, dishwashers and electric vehicle chargers until after 8:00 pm.More frequent, longer-lasting and more intense heat waves are one of the clearest signs of climate change, with Europe also recently hard hit.Global average surface temperatures have risen roughly 2.5F above pre-industrial averages as a result of human-caused climate change, mainly driven by the burning of fossil fuels.Records set to fall