The monsoon is late again. Without the almost biblical rains, there is nothing to break the heat during a long stretch of days above 43°C (109°F). The pavement is scalding. Hospital wards are filling with burn victims. Even the cacti seem crispy. Many people venture out only in the early morning, before the sun rises. The rest of the time they take refuge in air-conditioned rooms: the invention that makes life in the desert possible.

This was the scene in Phoenix, Arizona in July 2023. But what if the demand for electricity to power those air-conditioners had stretched the grid to breaking point? A study published in Environmental Science and Technology, a journal, suggests that a five-day heatwave in Phoenix, with a blackout, could kill more than 13,000 people and send more than half of the city’s residents to hospital.

This is Phoenix’s worst-case scenario. But heatwaves do not not need to cause catastrophic power loss to threaten people’s lives. The urban heat-island effect means that city centres can be much hotter than surrounding areas because roads and buildings absorb and trap heat. Los Angeles, Miami and Phoenix have hired “chief heat officers” to oversee emergency response and adaptation plans. In 2024, which may be the hottest year on record, more cities will appoint such officials. Ever more will adopt new technology such as cool pavements, which reflect rather than absorb sunlight. Trees will be planted for shade. City officials will open more cooling centres and try to coax unsheltered homeless people, who are among the most vulnerable to heat exhaustion, inside.

But 2024 will also bring political challenges. In America there are no federal heat protections for workers. President Joe Biden has directed the Occupational Safety and Health Administration to create a national standard for worker heat-safety, but that could take years. And if Mr Biden loses the election, pending climate regulation may be scrapped. Things look only mildly better at the state level. Just five states have enacted such worker protections; all of them are run by Democrats.

Some cities in Republican-led states are taking matters into their own hands. “The state hasn’t really addressed extreme heat or carbon mitigation at all,” says Jane Gilbert, the chief heat officer for Florida’s Miami-Dade County. Yet she was the first in the world to hold her title, and, along with the mayor, has made heat a priority for the county.

Miami and Phoenix at least know that their summers will be hot. But climate change is also bringing extreme heat to places unaccustomed to it. The First Street Foundation, a non-profit group, reckons that an “extreme heat belt” will emerge in the centre of America over the next 30 years (see map). Perhaps these places, too, will soon have heat chiefs of their own.