From Miami to Melbourne, a quiet revolution is underway to fend off a silent and invisible killer

A quiet revolution is underway to address a widely underestimated climate challenge: extreme heat.

Local authorities have appointed several chief heat officers (CHOs) in cities worldwide in recent years to prepare residents for increasingly frequent and severe bouts of excessive heat.

"They call it the silent killer," said Eleni Myrivili, who serves as the global CHO for the U.N.'s human settlement program and previously worked in a similar role for the Greek capital of Athens.

Myrivili said she believes that extreme heat is often overlookedbecause it lacks the visible drama of roofs being ripped from homes or streets being turned into rivers.

"Heat, I believe it to the bottom of my heart, is going to be the number one public health challenge that we will be dealing with in the next decade. And we need to prepare for it now," Myrivili told CNBC via videoconference. "We can — but we really need to make it a priority."

Heat is the leading weather-related killer in the U.S. Data from the Centers for Disease Control and Prevention showed that more than 1,700 deaths were the result of heat-related causes in 2022, roughly double the toll of five years prior. Researchers have said these are likely conservative estimates.

The CDC defines extreme heat as summertime temperatures that are significantly hotter and/or more humid than average.

Older adults, young children and people with chronic diseases are recognized as among the most at risk of heat-related illnesses, such as heat exhaustion or heat stroke. The CDC warns that even young and healthy people can be affected.

The first person in the world to be assigned as a CHO was Jane Gilbert, who was appointed in 2021 to oversee Florida's most populous county, Miami-Dade.

The CHO role was