The future is hot.

As climate change heats up the globe, Californians can expect to face longer and more extreme heat waves like the ones sweeping through parts of the state this summer, experts warn.

Seniors, who are more prone to heat stress than younger adults, will be among those most affected by rising temperatures. With the over-65 population projected to expand rapidly in the coming decades, the accompanying hotter weather could place an enormous burden on emergency and health care infrastructure.

Extreme heat already causes more deaths than any other weather-related hazard including hurricanes, tornados and floods. A recent study in the journal Science estimated heat-related deaths would become as numerous as deaths from automobile accidents by the end of the century. That will exact a heavy economic toll if preventative measures aren’t taken, the researchers said. For example California’s 10-day heat wave in 2006 racked up an estimated $133 million in health-related costs, and killed more than 650 people.

“Literally every decade we have more record-breaking years with respect to temperatures,” said Aradhna E. Tripati, a climate scientist at UCLA. “We’re already paying a cost and it’s going to keep going up.”

Seniors are especially vulnerable during heat waves because they have a harder time than younger adults adjusting to sudden changes in temperature. They also frequently suffer from chronic medical conditions and take prescription drugs that change the body’s normal responses to heat.

For low-income seniors the risk of heat stress is particularly high, said Jeffrey Gunzenhauser, interim health officer for Los Angeles County. These seniors are more likely than their wealthier peers to lack air conditioning and live in urban areas without trees and green space that provide a cooling effect.

In Los Angeles, the average number of days per year when temperatures rise above 95 degrees Fahrenheit is predicted to skyrocket from 6 at the start of the millennium to 54 by the end of the century, effectively adding a new season of extreme heat, a recent study found. Inland areas are expected to experience even more extremely hot days.

For now, Gunzenhauser said local authorities are well equipped to handle extreme heat situations. Temperatures are tracked rigorously, he said, and the county has a network of 75 to 100 cooling centers that offer residents shelter from high heat. But if the number of extreme temperature days increases to the levels predicted in the future and the senior population keeps growing, it will likely become much harder for authorities to deal with, he said.

“We’re going to need a lot more community help,” Gunzenhauser said.

In 2013, the California Department of Public Health (CDPH) and the California Environmental Protection Agency published guidelines for state and local authorities on how to prepare for more extreme heat. These include updating green building codes to require greater energy efficiency, planting trees and creating green space in urban areas to help mitigate heat, encouraging the use of less heat-absorbing pavement materials, and improving emergency alert and response systems.

CDPH spokesman Ronald Owens said the state is also engaged in a pilot project with Contra Costa County to provide weatherization services such as insulation and window sealing to people particularly sensitive to climate impacts, such as those with cardiovascular disease, respiratory illnesses and kidney disease.

Tripati, the UCLA scientist, said more green spaces and cooler building materials could be particularly effective in reducing the impact of extreme heat on urban centers. However, those changes need to begin now, she said.

Heat waves “are already impacting senior citizens, and they will be impacting more and more of them,” Tripati said. “This is not something that we have until the end of the century to deal with.”