Cities will feel the effects most of all because they already warm up faster than the surrounding countryside as pavement and concrete absorb incoming solar radiation. By 2050, the heat-stress index for cities will increase twice as much as for adjacent rural areas, says Hendrik Wouters, a postdoctoral researcher at the University of Leuven in Belgium, whose research involves a fairly simple metric to help cities prepare for the consequences of global warming.

“Heat waves are already affecting our cities today. We see power surges, other failure of infrastructure, and we know hospital admissions spike,” Wouters says. “We also know the urban heat-island effect becomes more intense and we wanted to quantify that, so we looked at how often temperature alarm levels are exceeded. When you count that, it gives you a measure of how much heat stress impact will evolve in the future.”

It’s time for for cities everywhere to start taking these challenges seriously, says Hanns Moshammer, with the Institute of Environmental Health at the University of Vienna.

“We need to reconsider our organization and infrastructure. What we are really concerned about are acute events like heat waves that require preparedness and communication, telling people what to do in advance.” For the long-term, doctors also need to consider indirect effects, like the spread of new diseases linked with increasing temperatures, Moshammer concludes.