At large events all over the world, the scenes of extreme heat stress are starting to look familiar. Older men, shirts undone, lying down with their eyes closed. Aid tents packed with the unconscious. And lines of the faithful — whether they seek religion, music, ballot boxes or sport — sweating under slivers of shade.

The consequences have been dire. At this year’s hajj, the Islamic pilgrimage in Saudi Arabia, at least 1,300 people died as temperatures surpassed 100 degrees Fahrenheit. And in many ways, that heavy toll was just the latest sign that crowd control and heat waves fueled by climate change are on a dangerous collision course.

During India’s recent election, dozens of poll workers died on the job. Last summer, troops of Boy Scouts visiting South Korea for a jubilee became sick from heat, as did others at music festivals in Australia, Europe and North America.

Even as heat kills more people today than any other extreme weather event, there is still a dangerous cultural lag. Many major-event organizers and attendees are still behind the climate curve, failing to contend with just how much a warming planet has elevated the risk to summer crowds.

“As the warm seasons get longer, as the heat waves come earlier, we’re going to have to adapt,” said Benjamin Zaitchik, a climate scientist at Johns Hopkins University who studies health-damaging climate events. Along with personal behavior, he added, infrastructure, emergency management and social calendars must “really acknowledge this new reality.”

Among the many low-tech ways to prevent sickness and death are shade, water stations, sidewalks painted white to reflect heat and emergency health services to treat severe cases of heatstroke. Some hot and innovative places, like Singapore, have constructed public spaces uniting the outdoors with the indoors. They have added air-conditioning to areas where people might have to spend time waiting, such as bus stops.