In June, a heat wave in the American southwest sent the mercury soaring over 115 degrees in parts of Arizona. At least four deaths were linked to that heat wave.

Considering that 2016 is predicted to be the hottest year on record worldwide, and that last month was declared the hottest June on record in the United States, how could climate change influence the number of heat-related deaths we see?

“It is difficult to predict,” says epidemiologist Elisaveta Petkova. “If we see an unprecedented heat wave, extremely high temperatures, longer duration, we may see a substantial number of people dying.”

Petkova says past heat waves have shown that heat poses a severe threat to public health, especially in urban areas.

This map of the Earth shows surface temperature trends between 1950 and 2014. Credit: Wikipedia/Creative Commons

“There have been a lot of historical heat waves. Even in Chicago in 1995 there's been a heat wave that took over 700 lives, so I don't think we are protected from heat,” Petkova says.

Petkova, who is project director at the National Center for Disaster Preparedness of Columbia University in New York, wanted to find out more about the potential for heat-related public health problems in the future. So she, together with experts on climate science, demography and statistics, put together a study to try and predict different scenarios for future heat waves.

According to their most extreme scenarios, some 3,000 people could die each year from heat waves.

“We have projections about population change, how many people would live in the city. We have projections about the different climate scenarios that were used — a higher and a lower greenhouse gas emission scenario, various climate models, and also different adaptation pathways,” Petkova says.

“This specific estimate [of 3,000 people dying annually] is a combination of being exposed to the higher greenhouse gas emission scenario, having a higher population in the city, not reaching a higher level of adaptation in the future ... it’s just a combination of different factors.”

Many people don’t think of heat as a health threat, but Petkova says over-exposure can be deadly.

“Heat exhaustion and heat stroke,” says Petkova. “But it is also important to remember that people with underlying health conditions may suffer from other types of diseases that are just exacerbated during the heat.”

Despite the dangers, Petkova says there are things we can do to prepare for even the worst-case scenario.

“We have to think about our cities, just making sure that we're working toward a future where we have cities that are more resilient, cities that are more sustainable, where we really have access to various types of adaptations that make the life of people better at the same time and really help with addressing climate change,” Petkova says.

“And something that every one of us can do is, we all have elderly neighbors, we have parents, people we may think are susceptible [to heat]. ... We can all just pay attention to those around us who may be at high risk and make sure that they know what they need to do to avoid such impacts.”

This article is based on an interview that aired on PRI's Science Friday.